Lennox 51M37 Merit Series Operation Manual PDF

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Lennox 51M37 Merit Series Operation Manual PDF

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Summary of Content for Lennox 51M37 Merit Series Operation Manual PDF

Page 1

05/05 505,050M

Page 1

2005 Lennox Industries Inc. Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE

51M37 Merit Series Thermostat

The Lennox Merit Series 5/2 day programmable electronic thermostat 51M37 provides excellent

temperature control and a large, easy-to-read display. It includes a programmable filter change reminder, an equipment maintenance reminder, and a system check indicator to notify the user when the equipment requires service.

The 51M37 is suitable for heat pump, 3-stage heat/2-stage cool applications using a gas or electric auxiliary heat source. An optional outdoor temperature sensor provides

auxiliary heat lockout, balance point operation, and dualfuel compatibility.

OPERATION MANUAL

51M37 Merit Series 5/2 Day Programmable Thermostat

CONTROLS 505,050M 05/05 Supersedes 03/05

Table of Contents

51M37 Series Thermostat 1. . . . . . . . . . . . . . . . . . . . . . General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . . Buttons, Backlight, Timers & Settings 2. . . . . . . . . . . . DAY/TIME Set Day and Time 2. . . . . . . . . . . . . . . . . . HEAT Heat Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . COOL Cool Mode 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . HOLD Temperature Hold Mode 5. . . . . . . . . . . . . . . . PROG Thermostat Programming 5. . . . . . . . . . . . . . . FAN Controlling Fan Operation 6. . . . . . . . . . . . . . . . . SETTINGS Filter and Maintenance Reminders 6. . . SETTINGS Balance Point 7. . . . . . . . . . . . . . . . . . . . . Service Indicator 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermostat RESET 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing/Installing Thermostat 7. . . . . . . . . . . . . . . . . Default Thermostat Settings 7. . . . . . . . . . . . . . . . . . . . Technical Specifications 8. . . . . . . . . . . . . . . . . . . . . . . . Thermostat Output Table 10. . . . . . . . . . . . . . . . . . . . . . .

General

These instructions are intended as a general guide and do not supersede local codes in any way. Consult authorities having jurisdiction before installation.

Check equipment for shipping damage. If you find any damage, immediately contact the last carrier.

Introduction

This document describes the operation of Lennox thermostat 51M37. Refer to the installation manual for instructions re- garding installation and wiring of the thermostat.

Initial Thermostat Power-up

When power is initially applied to the thermostat, the dis- play will appear as shown in figure 1.

FAN ON AUTO

SYSTEM COOL OFF EMG. HEAT

I8:88

88 Figure 1

AM PM

ROOM

MO TU WE TH FR SA SU

SETPOINT

Initial PowerUp Display

SERVICE

FILTER

MAINT

Hi Lo

PROG A | B | C | D HOLD

All display segments are momentarily activated. This oc- curs as a normal part of thermostat initialization.

Litho U.S.A.

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505050M 5/1/05

Within a few seconds, the Home Screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed.

NOTE Tables 2 and 3 on page 8 show all system and

programming defaults.

I2:00 PROG A B C D HOLD

FAN ON AUTO

SYSTEM COOL OFF

HEAT70

Home Screen

Figure 2

ROOM

SERVICE

FILTER

MAINT MO TU WE TH FR SA SU

AM PM

At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.

NOTE Temperature scale default is Fahrenheit units but

may be reset to show Celsius, if desired. See page 8.

Buttons, Backlight, Timers & Settings

Buttons are located behind the small door on the right hand side of the thermostat (see figure 3).

IMPORTANT Do NOT begin pressing buttons until after you read the following section describing each button.

A pale blue display backlight illuminates for 30 seconds

each time any button is pressed.

When PROG or DAY/TIME is pressed, a field begins flash- ing, expecting another input. Start making changes within 15 seconds or the HOME screen will return.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Thermostat Buttons

Figure 3

(DOOR OPEN)

When an Arrow, HOLD, HEAT, or COOL button is pressed, SETPOINT and the temperature setting appears for 15 seconds. If desired, start making changes within 15 sec- onds or the HOME screen will return. The backlight will turn off 15 seconds after the HOME screen reappears.

DAY/TIME Setting the Day and Time

Press the DAY/TIME button and set the CURRENT hour, minute, and day of week as follows:

1. AM12" will flash on the screen. Press the Up/Down ar- rows buttons to change the hour. (AM" or PM" must correspond to time of day.) Press DAY/TIME OR, if ad- justing for daylight savings time, pressing ENTER stores the single change and exits to the HOME screen, bypassing minutes and day of week.

2. Minutes will flash. Use the Up/Down arrow buttons to display the minutes past the hour. Press DAY/TIME.

3. Day MO" (Monday) will flash. Use Up/Down arrow buttons to display the current day. Day selections are abbreviated as MO, TU", WE", TH", FR", SA", and SU". Press DAY/TIME.

4. The HOME screen reappears; confirm day and time are correct. This completes day and time setting.

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51M37 SERIES 5/2

HEAT Using the Heat Mode

Normal Heat Mode In normal heat mode, both the heat pump and the backup heat source are used to provide heat. If the thermostat de-

tects that the heat pump is not able to provide enough heat (as may be the case in very cold weather), then the backup heat source is activated.

Emergency Heat Mode In emergency heat mode, only the backup heat source provides heat the heat pump is disabled. The backup heat source is activated only when there is a heat demand.

Enabling Normal Heat Mode

Use the HEAT button to select normal heat mode, emer- gency heat mode, or to disable heat modes as desired. If the thermostat is in OFF or COOL mode, pressing the Heat

button enables Heat mode. This is indicated by HEAT in the SYSTEM box as shown in figure 4.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Normal Heat Mode Enabled

Figure 4

5:30

66 70

HOLD

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM

HEAT

Enabling Emergency Heat Mode

If the thermostat is in heat mode, pressing the Heat button

enables EMG. HEAT mode (see figure 5). If the thermostat is in normal heat mode when the HEAT button is pressed, then emergency heat mode is enabled.

SYSTEM COOL OFF EMG. HEAT62

Emergency Heat Mode Enabled

Figure 5

ROOM

75 SETPOINT

Disabling Heat Mode

If the thermostat is in emergency heat mode when the HEAT button is pressed, then heat modes are disabled. This is indicated by OFF in the SYSTEM box as shown in figure 6.

SYSTEM COOL OFF

HEAT75

Heat Mode Disabled

Figure 6

ROOM

75 SETPOINT

Heating Demand

The thermostat must be in either normal or emergency heat mode in order to properly control the heating equip- ment. In either heat mode, when the actual temperature is lower than the temperature setpoint (as shown in figure 7), the thermostat detects a heating demand and activates the heating equipment to satisfy the demand. Heating opera- tion is indicated by a flame icon in the SYSTEM box.

SYSTEM COOL OFF

HEAT72 Figure 7

ROOM

75 SETPOINT

Heating Demand

When the actual temperature rises above the temperature setpoint, the flame icon will disappear. This indicates that

the heating demand has been satisfied and that the heat- ing equipment has been turned off.

Heat pump operation is locked out for 5 minutes after a de- mand has been satisfied. If another heat pump demand occurs during this 5minute interval, the flame icon will flash; however, the heat pump will not run until the 5min- ute delay has elapsed.

NOTE The heat pump is activated for at least 4 minutes if

no buttons are pressed during the demand interval. The

backup heat source is activated for at least 3 minutes if no

buttons are pressed during the demand interval.

If your system supports 3stage heating (as does the 51M37 thermostat), you may notice various heating levels being delivered during a demand.

If a small heat pump heating demand is present, "Lo" is dis- played in the SYSTEM box; if a large heat pump heating

demand is present, "Hi" is displayed (see figure 8).

Large Heat Demand

Figure 8

ROOM

75 SETPOINT

SYSTEM COOL OFF

HEAT

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505050M 5/1/05

COOL Using the Cool Mode

Enabling and Disabling Cool Mode

Use the COOL button to enable or disable cool mode as desired. If the thermostat is in HEAT or OFF mode, cool mode is enabled when the COOL button is pressed. This is indicated by COOL in the SYSTEM box (see figure 9).

Turn Cool ON/OFF

Figure 9

I0:30

75 70

HOLD

AM PM

SETPOINTROOM

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

FAN

AUTO

SYSTEM COOL

If the thermostat is in cool mode, pressing the Cool button disables COOL mode (indicated by OFF in the SYSTEM box see figure 10).

SYSTEM COOL OFF

HEAT75

Cool Mode Disabled

Figure 10

ROOM

75 SETPOINT

Cooling Demand Set the thermostat to cool mode to control the cooling equipment. Then, if the room temperature is higher than the temperature setpoint, as shown in figure 11, the ther- mostat detects a cooling demand and will activate the cool-

ing equipment to satisfy the demand.

i0:00 PROG A B C D HOLD

Cooling Demand

Figure 11

ROOM

70 SETPOINT

FAN ON AUTO

SYSTEM COOL OFF

HEAT

AM PM

MO TU WE TH FR SA SU

Cooling operation is indicated by flashing snowflake"

icons in the SYSTEM box. When the actual temperature drops below the temperature setpoint, the snowflake icons will disappear. This indicates that the cooling demand has been satisfied and that the cooling equipment has been turned off.

If your system supports 2stage cooling (as does the 51M37 thermostat), you may notice various cooling levels

being delivered during a demand. Also, if a small cooling demand is present, "Lo" will be displayed in the SYSTEM box. However, if a large cooling demand is present, "Hi" will be displayed in the SYSTEM box (shown in figure 11).

NOTE If no buttons are pressed during a demand for

cooling, the equipment must operate for at least 4 minutes.

After a demand has been satisfied, cooling equipment op-

eration is locked out for 5 minutes. If another cooling de-

mand occurs during this 5minute interval, COOL" and the

snowflakes will flash; however, the cooling equipment will

not operate until the 5minute delay has elapsed.

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51M37 SERIES 5/2

HOLD Using Temperature Hold Modes

When HOLD is displayed at the HOME screen, the ther- mostat is in a temperature hold condition. This means that the temperature program data is ignored and the thermo- stat functions much like a nonprogrammable thermostat.

Adjusting Temperature Setpoint in Hold Mode

The temperature setpoint represents the desired tempera- ture of the space around the thermostat. The default tem- perature setpoint in Hold mode is 70F.

To adjust the setpoint, press the UP or DOWN () arrow

buttons (see figure 12); the existing setpoint is displayed to the right of the actual room temperature. Each button press adjusts the setpoint up or down by 1 degree.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Hold Temperature Mode

Figure 12

I0:36

72 68

HOLD

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM COOL

After the desired setpoint is reached, the HOME screen will reappear after about 15 seconds.

Permanent Hold Mode

At any time the program is running, from the HOME screen, set a permanent hold (program override) by press-

ing the HOLD button (see figure 12). The thermostat now functions much like a nonprogrammable thermostat. Use the Up/Down arrow buttons to adjust the hold setpoint. To return to the program, press HOLD again.

Temporary (2-Hour) Hold

At any time the program is running, from the HOME screen, set a temporary 2-hour hold by pressing the Up/ Down arrow buttons until the desired setpoint is displayed; HOLD" flashes (see figure 13). This overrides the pro-

gram for 2 hours from the last button press, then returns to the program.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Temporary Hold Temperature Mode

Figure 13

I0:36

72 68

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM COOL

PROG B HOLD

While in Temporary Hold, press HOLD once to switch to Permanent Hold (HOLD displays solid; PROG not dis- played); press HOLD again to return to the program

(PROG displays; HOLD not displayed).

PROG Thermostat Programming

The 51M37 thermostat can be programmed to perform a set of either heating or cooling events (but not a combination of heat and cool) for 5 consecutive days using a set of 4 unique events per day. The remaining 2 days can then be set for a different set of 4 unique events per day.

Both the consecutive days and the events/temperature are set by the homeowner.

To Change Consecutive Days...

To alter the 5 consecutive days, press and hold the PROG button for 5 seconds. The 5 consecutive day period

is then displayed (default is MOnday thru FRiday). To change to a different 5-consecutive days, use the Up/ Down arrow buttons. Any 5 consecutiveday span may be selected, for example, in figure 14, Saturday through Wednesday is defined as the 5day programming (Thurs- day and Friday would constitute the 2day programming). Press the PROG button when finished.

Change Consecutive days

Figure 14

FILTER MO TU WE TH FR SA SU

To Set Program Events and Temperatures...

Figure 15 gives an example of how the two sets of pro- grams can be set for a normal workweek and weekend.

In the 5day bar graph, note how programs A and C reflect the desired warmth while the home IS occupied (72); B allows less heating while the home is NOT occupied; D re- flects a cooler sleeping temperature. The 2day bar graph would support daylong occupancy and, because the first

program begins later, a lessdemanding time schedule.

Figure 15

5/2 Program Example 5DAY PROGRAM:

| A | B | C | D |

2DAY PROGRAM:

| A | B | C | D |

6AM NOON 6PM MID 6AM NIGHT

NOTE Pressing ENTER during the following program-

ming steps, saves and exits to the HOME screen.

To program events and temperatures, perform the follow- ing steps, once with Cool selected and once with Heat se- lected.

1. Press and release PROG. AM 6:00", period A", and the 5 consecutive days are displayed; AM 6" flashes.

2. Use the Up/Down arrow buttons to select the desired hour; press PROG when the desired hour is reached.

3. Use the Up/Down arrow buttons to select the desired minute; press PROG.

4. Use the Up/Down arrow buttons to select the desired temperature setpoint; press PROG.

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505050M 5/1/05

5. Repeat steps 2 through 4 for periods B, C, and D.

6. Repeat steps 1 through 5 for the 2day program.

NOTE This thermostat will NOT automatically switch

from heating to cooling, or vice versa; operator involve-

ment is required. At the change of seasons, or to accomo-

date abnormal seasonal temperature swings, you must

manually select to the opposite conditioning (Heat or Cool)

program.

FAN Controlling the Fan Operation

Use the FAN button to select either continuous fan mode or auto fan mode.

To change from continuous to auto fan mode (or vice ver- sa), press the FAN button. Note whether a fan icon in the FAN box is present (indicating that the fan is running) or not (fan not running).

If continuous fan mode is enabled (ON displayed in FAN box see figure 16), the fan will run continuously regard- less of whether the heating or cooling equipment is run-

ning.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Using Fan ON

Figure 16

I0:I0

PROG B

AM PM

ROOM

FAN ON

SYSTEM

HEAT

If auto fan mode is selected (AUTO displayed in FAN box

see figure 17), the fan will only run when the heating or cooling equipment is running.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Using Fan Auto

Figure 17

I0:36

AM PM

ROOM

FAN

AUTO

SYSTEM COOL

PROG B

SETTINGS Filter/Maintenance Reminders

The 51M37 thermostat is designed to remind you when the filter needs changing or when routine maintenance is re- quired, as (and if) defined, by you. These optional remind- ers are not enabled until you activate them. To do so, press

the Settings button (shown below the Fan button in figure 17) once or twice for the desired reminder as shown in fig- ure 18 and as described in table 1.

Reminder Settings Display

Figure 18

FILTER

OFF MAINT

For FILTER, press Settings button 1 time

For MAINT, press Settings button 2 times

The default setting for the reminders is OFF (disabled). Press Up/Down arrow buttons to select the desired re- minder intervals.

Table 1

Filter and Maintenance Reminders

Buttons to Use Reminder

Available Settings and How to Use

Settings (1st press)

FILTER Total fan run time expressed in months (Off 1 3 6 12); for

then Arrows to scroll

, , , , example, if fan runs 12 hours a day 1 month reminder displays

selections ,

in 2 calendar months.

Settings (2nd press)

MAINT Elapsed chronological time in months (Off 6 12) Use this

then Arrows to scroll

, , . , for example, to remind yourself when to perform routine checks

selections

or when to call a technician for di tipero c preven ve

maintenance.

Enter Stores settings.

NOTE The HOME screen will reappear about 15 seconds

after the final arrow button press. OR, press ENTER at any

time to store any changes and exit to the HOME screen.

After either programmed interval has elapsed, the remind-

er will be displayed as shown in figure 19.

I0:i2 PROG A B C D HOLD

FAN ON AUTO

SYSTEM COOL OFF

HEAT78

Reminders

Figure 19

ROOM

SERVICE

FILTER

AM PM

MO TU WE TH FR SA SU MAINT

After the filter has been changed or maintenance per-

formed, reset the reminder by pressing the SETTINGS button for 4 seconds. The screen will blink for a few mo- ments to indicate that the timer has been reset.

Page 7

51M37 SERIES 5/2

SETTINGS Balance Point

NOTE The balance point is only available with the out-

door sensor.

If the optional outdoor sensor (X2658) is connected to the thermostat, balance point adjustment is available. The bal- ance point feature allows the measured outdoor tempera-

ture to govern operation of the heat pump and backup heat source.

Use the SETTINGS button to access the balance point setting. If the outdoor sensor is attached to the thermostat, press the SETTINGS button three times to access the Bal- ance Point Settings screen (see figure 20).

Figure 20

ROOM

55 SETPOINT

Balance Point Setting

The balance point can be set at any temperature between 1F and 55F (17C to 13C). A balance point setting of zero disables the balance point function (in this case, the

thermostat behaves as if no outdoor sensor is attached). The default balance point setting is 55F.

To adjust the balance point up or down, press the Up/Down arrow buttons to the right of the display screen. The bal- ance point setting increases by 1F each time the Up but- ton is pressed and decreases by 1F each time the Down button is pressed.

After the desired balance point is reached, the HOME screen will reappear after about 15 seconds.

NOTE The balance point feature allows the outdoor tem-

perature to rise or fall 3F above or below the balance

point. This prevents excessive cycling of the equipment

when the outdoor temperature is near the balance point.

For example, if the balance point is 40F and the actual

outdoor temperature is 35F, the outdoor temperature

must rise to 43F before equipment adjustment occurs.

Conversely, if the balance point is 40F and the actual out-

door temperature is 45F, the outdoor temperature must

drop to 37F before equipment adjustment occurs.

Service Indicator

When abnormal equipment operation is detected, the SERVICE indicator will flash on the screen (see figure 21).

This indicates that the equipment requires service from a qualified service technician.

I0:i4 PROG A B C D HOLD

Service Indicator Flashing

Figure 21

ROOM

SERVICE

FILTER

AM PM

FAN ON AUTO

SYSTEM COOL OFF

HEAT

MO TU WE TH FR SA SU

Thermostat RESET

Under some abnormal conditions, it may be necessary to

reset" the thermostat to its default condition. Such a RE- SET would delete all programming and settings and there- fore should only be used on rare occasions when the the thermostat fails to function as designd and/or as pro- grammed. Such an instance can occur as a result of a pow- er surge or similar electrical disturbance (e.g. after an elec- trical storm or power outage). The RESET button can be

used to recover from this situation.

CAUTION When the RESET button is pressed, ALL settings re- vert back to the defaults, including the default pro- gram (see tables 2 and 3).

The RESET button is an unlabeled, recessed button lo-

cated behind the door, on the righthand side of the ther- mostat, below the SETTINGS button (see figure 3). Use a paper clip or small pencil to press the RESET button; ALL thermostat settings will be reset to the defaults listed in the Default Thermostat Settings section.

Removing/Installing Thermostat

The thermostat hinges on tabs on the top of the subbase; no tool is needed to remove the thermostat from the sub- base. Pivot the bottom of the thermostat outward (releas- ing the snaps), then lift up to remove.

To replace it, first position the top tilted toward the wall bracket and align it until you feel the tabs and slots engage;

then, while the top is in place, pivot the bottom toward the wall until the thermostat snaps into place.

Page 8

505050M 5/1/05

Default Thermostat Settings

Default thermostat settings are shown in table 2 and the default program is shown in table 3.

Table 2

Default Thermostat Settings

Mode Heat (Permanent Hold Mode)

Setpoint 70F (or 21C)

Fan Auto

Filter Reminder OFF

Maintenance Reminder OFF

Equipment Protection Timers

Reset Back to Zero

Table 3

Default Program Settings

Programs Time Temperature (Heat)

Temperature (Cool)

Weekday A 6:00am 70F / 21C 78F / 26C Weekday B 8:00am 62F / 17C 85F / 29C Weekday C 6:00pm 70F / 21C 78F / 26C Weekday D 10:00pm 62F / 17C 82F / 28C Weekend A 6:00am 70F / 21C 78F / 26C Weekend B 8:00am 62F / 17C 85F / 29C Weekend C 6:00pm 70F / 21C 78F / 26C Weekend D 10:00pm 62F / 17C 82F / 28C Weekday Monday, Tuesday, Wednesday,

Thursday, Friday

Weekend Saturday, Sunday

Technical Specifications

Thermostat Type

Electronic programmable thermostat for heat pump,

3-stage heat/2-stage cool.

NOTE 2 stages of heat pump heat and one stage of auxil-

iary (gas or electric) backup heat are supported.

Power Supply Range

18VAC 30VAC (24VAC nominal), 60Hz

CAUTION 24VAC is present on the terminals of the thermostat bracket. If removing the thermostat from the wall, use caution and avoid touching any of the connec- tor terminals on the wall bracket.

Also, when working with the thermostat dip switches, use a nonconductive tool and take cau- tion to avoid making any contact with the circuit board, its imprinted circuitry and its connector prongs.

Temperature Display Display Scale: Fahrenheit or Celsius user selectable (via

DIP switch; see figure 22) Display range: 35F (2C) to 99F (37C) Display resolution: 1F (1C) Display Accuracy: +/1F

If the Fahrenheit/Celsius display must be changed, use a plastic, nonconductive tool to push the dip switch to the right position (see figure 22).

F/C (Fahrenheit/Celsius) switch shown in Celsius position

Figure 22

Changing Fahrenheit/Celsius Setting

6 PLUG IN (Use Care To Avoid Bending Prongs.)

Temperature Measurement Range Measurement Scale: Fahrenheit Measurement Range: 35F to 99F Measurement Resolution: 0.5F

Measurement Accuracy: +/1F Field Offset: via DIP switches to +/3F Sampling Method: temperature measurements sampled every 15 seconds. Displayed temperature is the average of the last four measurements.

Temperature Setpoint Range Setting range: 50F (10C) to 90F (32C) Setting resolution: 1F (1C)

Page 9

51M37 SERIES 5/2

will react to a program event before the event occurs such that the desired temperature is reached at the time of the event, not after.

Fan Control AUTO or ON modes.

I/O Relays All thermostat relays are latching type to minimize power consumption.

Table 4

51M37 Terminal Designations

Term. Description

B Reversing valve, heat active

O Reversing valve, cool active

R 24VAC

Y1 First-stage cooling/heating, compressor energized

W1* Auxiliary heating, furnace energized

Y2 Second-stage cooling/heating, compressor energized

E* Emergency heat

G Fan control

L Service Indicator

C 24VAC common

T Outdoor temperature sensor connection 1

T Outdoor temperature sensor connection 2

* For most applications, E will be jumpered to W1. If sep-

arate wires are not provided for both E and W1, jumper

the E terminal to the W1 terminal on the thermostat sub-

base. For applications involving the use of a balance

point (whereby the outdoor temperature is to be used to

restrict either heat pump operation or backup heat

source operation), the optional outdoor sensor (part

number X2658) MUST be installed.

Equipment Protection Timers Minimum Compressor OFF time: 5 minutes Minimum Compressor ON time: 4 minutes

Minimum Furnace ON time: 3 minutes

Minimum furnace cycle time (elapsed time between any furnace activation and the next furnace activation): 6 min- utes.

Minimum elapsed time between any compressor activa- tion and the next compressor activation: 6 minutes.

NOTE All protection timers (except the compressor OFF

timer) can be overridden if a heating or cooling demand is

initiated or terminated using the UP, DOWN, HEAT, or

COOL buttons.

Equipment Protection Override

Both the minimum compressor OFF timer and the mini- mum equipment cycle timer can be overridden by press- ing and holding either the HEAT or COOL button down for 4 seconds.

OverTemperature Protection

Thermal-mechanical switch opens W1, Y1, Y2, and E at 93F+/6F.

Filter Reminder

Settings of Off, 1, 3, 6 or 12 (months of fan run time) are available. When programmed time has elapsed, a FILTER indicator is displayed.

Maintenance Reminder

Settings of Off, 6 or 12 (months of chronological time) are available. When programmed time has elapsed, a mainte- nance indicator MAINT" is displayed.

Service Reminder

The SERVICE indicator is displayed only under the follow- ing conditions:

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the R terminal;

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the C terminal.

Power Loss/Recovery

Thermostat memory is retained for a minimum of 24 hours during a power loss (includes retention of program infor- mation, HOLD status, programmed temperature setpoint,

heat/cool and fan mode settings, filter reminder status, maintenance reminder status, and equipment protection timers). After 24 hours of power loss, programmed settings will be lost and replaced with default settings.

IMPORTANT Power must be applied for at least six consecutive hours prior to a power loss in order for memory to be retained for the specified time.

LCD Backlight

Activated for 30 seconds when any button is pressed.

NOTE During an electrical storm or similar disturbance,

the backlight may activate for a few seconds. This is nor-

mal and will no longer occur after the electrical disturbance

has passed.

Thermostat Operating Conditions

35F to 105F, 5% to 90% RH

Thermostat Storage Conditions

40F to 185F, 5% to 95% RH

Page 10

505050M 5/1/05

Thermostat Output Table

Table 5 depicts the 51M37 thermostat output states for var- ious input conditions. The following notes described terms used in the table.

NOTES:

X = output is activated with 24VAC.

BBP: outdoor temperature is below balance point

ABP: outdoor temperature is above balance point

In all cases, the state of the B terminal is opposite that of the O terminal

Data are tabulated for AUTO fan setting. If the fan set- ting is ON, the G output is activated in all cases

Upstage timers:

30 minutes (when upstaging from small to large demand)

15 minutes (HEAT MODE ONLY when upstaging from large to very large demand)

The temperature ranges expressed in the following definitions of SMALL/LARGE/VERY LARGE" de- mands are for guidance only; actual temperatures may vary:

With a small HEAT demand, temperature is: below setpoint 0.5F but above setpoint 1.5F AND 30-minute upstage timer HAS NOT expired.

With a large HEAT demand, temperature is: less than setpoint 1.5F OR 30-minute upstage timer HAS expired.

With a very large heat demand, temperature is: below setpoint 2.5F OR 15minute 2nd upstage timer HAS expired.

Emergency heat demand (only if emergency heat is enabled): temperature is below setpoint 0.5F.

With a small COOL demand, temperature is: above setpoint +0.5F but below setpoint +1.5F AND 30-minute upstage timer HAS NOT expired.

With a large COOL demand, temperature is: above setpoint +1.5F OR 30-minute upstage timer HAS expired.

Table 5

THERMOSTAT OUTPUTS

Demand Condition W1 E Y1 Y2 G O

Cooling Demands

SMALL X X X

LARGE X X X X

No Demand X

Heating Demands

w/Electric Backup (no outdoor sensor)

SMALL X X

LARGE X X X

Very LARGE X X X X

Emergency X X

No Demand

w/Gas Backup (dual fuel; no outdoor sensor)

SMALL X X

LARGE X X X

Very LARGE X

Emergency X

No Demand

w/Electric Backup (outdoor sensor attached)

SMALL (Above Balance Point) X X

LARGE (ABP) X X X

Very LARGE (ABP) X X X

SMALL (Below Balance Point) X X

LARGE (BBP) X X X

Very LARGE (BBP) X X X X

Emergency X X

No Demand

w/Gas Backup (dual fuel; outdoor sensor attached)

SMALL (ABP) X X

LARGE (ABP) X X X

Very LARGE (ABP) X

SMALL (BBP) X

LARGE (BBP) X

Very LARGE (BBP) X

Emergency X

No Demand

Page 11

05/05 505,049M

Page 1

2005 Lennox Industries Inc. Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE

51M35 Merit Series Thermostat

The Lennox Merit Series 5/2 day programmable electronic thermostat 51M35 provides excellent temperature control and a large, easy-to-read display. This product includes a programmable filter change reminder, an equipment maintenance reminder, and a system check indicator to notify the user when the equipment requires service.

Thermostat 51M35 is suitable for non-heat pump, two- stage heat/two-stage cool applications using a gas or elec- tric furnace.

OPERATION MANUAL

51M35 Merit Series 5/2 Day Programmable Thermostat

CONTROLS 505,049M 05/05 Supersedes 03/05

Table of Contents

51M35 Series Thermostat 1. . . . . . . . . . . . . . . . . . . . . . General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . . Buttons, Backlight, Timers & Settings 2. . . . . . . . . . . . DAY/TIME Set Day and Time 2. . . . . . . . . . . . . . . . . . HEAT Heat Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . COOL Cool Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . HOLD Temperature Hold Mode 4. . . . . . . . . . . . . . . . PROG Thermostat Programming 4. . . . . . . . . . . . . . . FAN Controlling Fan Operation 5. . . . . . . . . . . . . . . . . SETTINGS Filter /Maintenance Reminder 5. . . . . . . Service Indicator 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermostat RESET 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing/Installing Thermostat 6. . . . . . . . . . . . . . . . . Default Thermostat Settings 6. . . . . . . . . . . . . . . . . . . . Technical Specifications 7. . . . . . . . . . . . . . . . . . . . . . . . Thermostat Output Table 8. . . . . . . . . . . . . . . . . . . . . . .

General

These instructions are intended as a general guide and do not supersede local codes in any way. Consult authorities having jurisdiction before installation.

Check equipment for shipping damage. If you find any damage, immediately contact the last carrier.

Introduction

This document describes the operation of Lennox thermostat 51M35. Refer to the installation manual for instructions re- garding installation and wiring of the thermostat.

Initial Thermostat Power-up

When power is initially applied to the thermostat, the dis-

play will appear as shown in figure 1.

FAN ON AUTO

SYSTEM COOL OFF EMG. HEAT

I8:88

88 Figure 1

AM PM

ROOM

MO TU WE TH FR SA SU

SETPOINT

Initial PowerUp Display

SERVICE

FILTER

MAINT

Hi Lo

PROG A | B | C | D HOLD

All display segments are momentarily activated. This oc-

curs as a normal part of thermostat initialization.

Litho U.S.A.

Page 12

Page 2

505049M 5/1/05

Within a few seconds, the Home Screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed.

NOTE Tables 2 and 3 on page 6 show all system and

programming defaults.

I2:00 PROG A B C D HOLD

FAN ON AUTO

SYSTEM COOL OFF

HEAT70

Home Screen

Figure 2

ROOM

SERVICE

FILTER

MAINT MO TU WE TH FR SA SU

AM PM

At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70F. At this point, if the equipment has been fully powered and if a heat

demand were present, the system would begin operating.

NOTE Temperature scale default is Fahrenheit units but

may be reset to show Celsius, if desired. See page 7.

Buttons, Backlight, Timers & Settings

Buttons are located behind the small door on the right hand side of the thermostat (see figure 3).

IMPORTANT Do NOT begin pressing buttons until after you read the following section describing each button.

A pale blue display backlight illuminates for 30 seconds each time any button is pressed.

When PROG or DAY/TIME is pressed, a field begins flash- ing, expecting another input. Start making changes within 15 seconds or the HOME screen will return.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Thermostat Buttons

Figure 3

(DOOR OPEN)

DAY/TIME Setting the Day and Time

Press the DAY/TIME button and set the CURRENT hour, minute, and day of week as follows:

1. AM12" will flash on the screen. Press the UP/DOWN arrows to change the hour. (AM" or PM" must corre- spond to time of day.) Press DAY/TIME OR, if adjust- ing for daylight savings time, pressing ENTER stores the single change and exits to the HOME screen, by- passing minutes and day of week.

2. Minutes will flash. Use the UP/DOWN arrow button to display the minutes past the hour. Press DAY/TIME.

3. Day MO" (Monday) will flash. Use UP or DOWN arrow buttons to display the current day. Day selections are abbreviated as MO, TU", WE", TH", FR", SA", and SU". Press DAY/TIME.

4. The HOME screen reappears; confirm day and time are correct. This completes day and time setting.

Page 13

Page 3

51M35 SERIES 5/2

HEAT Using the Heat Mode

Enabling and Disabling Heat Mode

The thermostat must be in the HEAT mode to control the heating equipment. Press the Heat button to enable or dis- able HEAT mode. If the thermostat is in COOL or OFF mode, pressing the Heat button enables the HEAT mode (indicated by HEAT in the SYSTEM box see figure 4).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Turn Heat ON/OFF

Figure 4

5:30

66 70

HOLD

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM

HEAT

If the thermostat is in heat mode, pressing the Heat button disables HEAT mode (indicated by OFF in the SYSTEM box see figure 5).

SYSTEM COOL OFF

HEAT75

Heat/Cool Mode Disabled

Figure 5

ROOM

75 SETPOINT

Heating Demand

Set the thermostat to heat mode to control the heating equipment. Then, if the room temperature is lower than the temperature setpoint, as shown in figure 6, the thermostat detects a heating demand and will activate the heating equipment to satisfy the demand.

SYSTEM COOL OFF

HEAT72 Figure 6

ROOM

75 SETPOINT

Heating Demand

Heating operation is indicated by a flame icon in the SYS- TEM box. When the actual temperature rises above the temperature setpoint, the flame icon will disappear. This indicates that the heating demand has been satisfied and that the heating equipment has been turned off.

If your system supports 2stage heating (as does the 51M35 thermostat), you may notice various heating levels being delivered during a demand.

NOTE Heating equipment is activated for at least 3 min- utes if no buttons are pressed during the demand interval.

COOL Using the Cool Mode

Enabling and Disabling Cool Mode Use the COOL button to enable or disable cool mode as desired. If the thermostat is in HEAT or OFF mode, cool mode is enabled when the COOL button is pressed. This is indicated by COOL in the SYSTEM box (see figure 8).

Turn Cool ON/OFF

Figure 7

I0:30

75 70

HOLD

AM PM

SETPOINTROOM

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

FAN

AUTO

SYSTEM COOL

If the thermostat is in cool mode, pressing the Cool button disables COOL mode (indicated by OFF in the SYSTEM box see figure 5).

Cooling Demand Set the thermostat to cool mode to control the cooling equipment. Then, if the room temperature is higher than the temperature setpoint, as shown in figure 8, the thermo-

stat detects a cooling demand and will activate the cooling equipment to satisfy the demand.

Cooling Demand

Figure 8

ROOM

70 SETPOINT

SYSTEM COOL OFF

HEAT

Cooling operation is indicated by flashing snowflake" icons in the SYSTEM box. When the actual temperature drops below the temperature setpoint, the snowflake icons will disappear. This indicates that the cooling demand has been satisfied and that the cooling equipment has been turned off.

If your system supports 2stage cooling (as does the

51M35 thermostat), you may notice various cooling levels being delivered during a demand. Also, if a small cooling demand is present, "Lo" will be displayed in the SYSTEM box. However, if a large cooling demand is present, "Hi" will be displayed in the SYSTEM box (shown in figure 8).

NOTE If no buttons are pressed during a demand for cooling, the equipment must operate for at least 4 minutes. After a demand has been satisfied, cooling equipment op- eration is locked out for 5 minutes. If another cooling de- mand occurs during this 5minute interval, COOL" and the snowflakes will flash; however, the cooling equipment will not operate until the 5minute delay has elapsed.

Page 14

Page 4

505049M 5/1/05

HOLD Using Temperature Hold Modes

Adjusting Temperature Setpoint in Hold Mode

The temperature setpoint represents the desired tempera- ture of the space around the thermostat. The default tem-

perature setpoint in Hold mode is 70F.

To adjust the setpoint, press the UP or DOWN () arrow buttons (see figure 9); the existing setpoint is displayed to

the right of the actual room temperature. Each button press adjusts the setpoint up or down by 1 degree.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Hold Temperature Mode

Figure 9

I0:36

72 68

HOLD

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM COOL

After the desired setpoint is reached, the HOME screen

will reappear after about 15 seconds.

Permanent Hold Mode

At any time the program is running, from the HOME screen, set a permanent hold (program override) by press- ing the HOLD button (see figure 9). The thermostat now functions much like a nonprogrammable thermostat. Use the Up/Down arrow buttons to adjust the hold setpoint. To return to the program, press HOLD again.

Temporary (2-Hour) Hold

At any time the program is running, from the HOME

screen, set a temporary 2-hour hold by pressing the Up/ Down arrow buttons until the desired setpoint is displayed; HOLD" flashes (see figure 10). This overrides the pro- gram for 2 hours from the last button press, then returns to the program.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Temporary Hold Temperature Mode

Figure 10

I0:36

72 68

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM COOL

PROG B HOLD

While in Temporary Hold, press HOLD once to switch to Permanent Hold (HOLD displays solid; PROG not dis- played); press HOLD again to return to the program (PROG displays; HOLD not displayed).

PROG Thermostat Programming

The 51M35 thermostat can be programmed to perform a set of either heating or cooling events (but not a combination of heat and cool) for 5 consecutive days using a set of 4 unique events per day. The remaining 2 days can then be set for a different set of 4 unique events per day. Both the consecutive days and the events/temperature are set by the homeowner.

To Change Consecutive Days... To alter the 5 consecutive days, press and hold the PROG button for 5 seconds. The existing 5 consecutive day peri- od is then displayed (default is MOnday thru FRiday). To change to a different 5-consecutive days, use the Up/ Down arrow buttons. Any 5 consecutiveday span may be selected, for example, in figure 11, Saturday through Wednesday is defined as the 5day programming (Thurs- day and Friday would constitute the 2day programming). Press the PROG button when finished.

Change Consecutive days

Figure 11

FILTER MO TU WE TH FR SA SU

To Set Program Events and Temperatures... Figure 12 gives an example of how the two sets of pro- grams can be set for a normal workweek and weekend.

In the 5day bar graph, note how programs A and C reflect the desired warmth while the home IS occupied (72); B allows less heating while the home is NOT occupied; D re- flects a cool sleeping temperature. The 2day bar graph would support daylong occupancy and, because the first program begins later, a lessdemanding time schedule.

Figure 12

5/2 Program Example

5DAY PROGRAM:

| A | B | C | D |

2DAY PROGRAM:

| A | B | C | D |

6AM NOON 6PM MID 6AM NIGHT

NOTE Pressing ENTER during the following program- ming steps, saves and exits to the HOME screen.

To program events and temperatures, perform the follow- ing steps, once with Cool selected and once with Heat se- lected.

1. Press and release PROG. AM 6:00", period A", and the 5 consecutive days are displayed; AM 6" flashes.

2. Use the Up/Down arrow buttons to select the desired hour; press PROG when the desired hour is reached.

3. Use the Up/Down arrow buttons to select the desired minute; press PROG.

4. Use the Up/Down arrow buttons to select the desired temperature setpoint; press PROG.

5. Repeat steps 2 through 4 for periods B, C, and D.

6. Repeat steps 1 through 5 for the 2day program.

Page 15

Page 5

51M35 SERIES 5/2

NOTE This thermostat will NOT automatically switch from heating to cooling, or vice versa; operator involve- ment is required. At the change of seasons, or to accomo- date abnormal seasonal temperature swings, you must manually select to the opposite conditioning (Heat or Cool) program.

FAN Controlling the Fan Operation

Use the FAN button to select either continuous fan mode or auto fan mode.

To change from continuous to auto fan mode (or vice ver- sa), press the FAN button. Note whether a fan icon in the FAN box is present (indicating that the fan is running) or not (fan not running).

If continuous fan mode is enabled (ON displayed in FAN box see figure 13), the fan will run continuously regard- less of whether the heating or cooling equipment is run- ning.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Using Fan ON

Figure 13

I0:I0

PROG B

AM PM

ROOM

FAN ON

SYSTEM

HEAT

If auto fan mode is selected (AUTO displayed in FAN box see figure 14), the fan will only run when the heating or cooling equipment is running.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Using Fan Auto

Figure 14

I0:36

AM PM

ROOM

FAN

AUTO

SYSTEM COOL

PROG B

SETTINGS Filter/Maintenance Reminders

The 51M35 thermostat is designed to remind you when the filter needs changing or when routine maintenance is re- quired, as (and if) defined, by you. These optional remind- ers are not enabled until you activate them. To do so, press the Settings button (shown below the Fan button in figure 14) once or twice for the desired reminder as shown in fig- ure 15 and as described in table 1.

Reminder Settings Display

Figure 15

FILTER

OFF MAINT

For FILTER, press Settings button 1 time

For MAINT, press Settings button 2 times

The default setting for the reminders is OFF (disabled). Press Up/Down arrow buttons to select the desired re- minder intervals.

Table 1

Filter and Maintenance Reminders

Buttons to Use Reminder

Available Settings and How to Use

Settings (1st press)

FILTER Total fan run time expressed in months (Off 1 3 6 12); for

then Arrows to scroll

, , , , example, if fan runs 12 hours a day 1 month reminder displays

selections ,

in 2 calendar months.

Settings (2nd press)

MAINT Elapsed chronological time in months (Off 6 12) Use this

then Arrows to scroll

, , . , for example, to remind yourself when to perform routine checks

selections

or when to call a technician for perodic preventive maintenance.

Enter Stores settings.

NOTE The HOME screen will reappear about 15 seconds after the final arrow button press. OR, press ENTER at any time to store any changes and exit to the HOME screen.

After either programmed interval has elapsed, the remind- er will be displayed as shown in figure 16.

I0:i2 PROG A B C D HOLD

FAN ON AUTO

SYSTEM COOL OFF

HEAT78

Reminders

Figure 16

ROOM

SERVICE

FILTER

AM PM

MO TU WE TH FR SA SU MAINT

After the filter has been changed or maintenance per- formed, reset the reminder by pressing the SETTINGS button for 4 seconds. The screen will blink for a few mo- ments to indicate that the timer has been reset.

Page 16

Page 6

505049M 5/1/05

Service Indicator

When abnormal equipment operation is detected, the SERVICE indicator will flash on the screen (see figure 17).

This indicates that the equipment requires service from a qualified service technician.

I0:i4 PROG A B C D HOLD

Service Indicator Flashing

Figure 17

ROOM

SERVICE

FILTER

AM PM

FAN ON AUTO

SYSTEM COOL OFF

HEAT

MO TU WE TH FR SA SU

Thermostat RESET

Under some abnormal conditions, it may be necessary to reset" the thermostat to its default condition. Such a RE- SET would delete all programming and settings and there- fore should only be used on rare occasions when the the thermostat fails to function as designd and/or as pro- grammed. Such an instance can occur as a result of a pow- er surge or similar electrical disturbance (e.g. after an elec- trical storm or power outage). The RESET button can be used to recover from this situation.

CAUTION When the RESET button is pressed, ALL settings re- vert back to the defaults, including the default pro- gram (see tables 2 and 3).

The RESET button is an unlabeled, recessed button lo- cated behind the door on the righthand side of the thermo- stat, below the SETTINGS button (see figure 3). Use a pa- per clip or small pencil to press the RESET button; ALL thermostat settings will be reset to the defaults listed in the Default Thermostat Settings section.

Removing and Installing Thermostat

The thermostat hinges on tabs on the top of the subbase;

no tool is needed to remove the thermostat from the sub- base. Pivot the bottom of the thermostat outward (releas- ing the snaps), then lift up to remove.

To install it, first position the top tilted toward the wall brack- et and align it until you feel the tabs and slots engage; then, while the top is in place, pivot the bottom toward the wall

until the thermostat snaps into place.

Default Thermostat Settings

Default thermostat settings are in table 2 and the default program is shown in table 3.

Table 2

Default Thermostat Settings

Mode Heat (Permanent Hold Mode)

Setpoint 70F (or 21C)

Fan Auto

Filter Reminder OFF

Maintenance Reminder OFF

Equipment Protection Timers

Reset Back to Zero

Table 3

Default Program Settings

Programs Time Temperature (Heat)

Temperature (Cool)

Thursday, Friday

Weekend Saturday, Sunday

Page 17

Page 7

51M35 SERIES 5/2

Technical Specifications

Thermostat Type

Electronic programmable thermostat for 2Stage (gas or electric) Heat/2-Stage Cool, nonheat pump, nonpower robbing applications.

Power Supply Range 18VAC 30VAC (24VAC nominal), 60Hz

CAUTION 24VAC is present on the terminals of the thermostat bracket. If removing the thermostat from the wall, use caution and avoid touching any of the connec- tor terminals on the wall bracket.

Also, when working with the thermostat dip switches, use a nonconductive tool and take cau- tion to avoid making any contact with the circuit board, its imprinted circuitry and its connector prongs.

Temperature Display Display Scale: Fahrenheit or Celsius user selectable (via DIP switch; see figure 18) Display range: 35F (2C) to 99F (37C)

Display resolution: 1F (1C) Display Accuracy: +/1F

If the Fahrenheit/Celsius display must be changed, use a plastic, nonconductive tool to push the dip switch to the right position (see figure 18).

F/C (Fahrenheit/Celsius) switch shown in Celsius position

Figure 18

Changing Fahrenheit/Celsius Setting

6 PLUG IN (Use Care To Avoid Bending Prongs.)

Temperature Measurement Range Measurement Scale: Fahrenheit Measurement Range: 35F to 99F Measurement Resolution: 0.5F

Temperature Setpoint Range

Setting range: 50F (10C) to 90F (32C) Setting resolution: 1F (1C)

Smart Setback Recovery (via DIP switch #6) Smart Setback Recovery (SSR) affects the way the ther- mostat responds to program events. If SSR is disabled, the thermostat will react to a program event at the time the event occurs. However, if SSR is enabled, the thermostat will react to a program event before the event occurs such that the desired temperature is reached at the time of the event, not after.

Fan Control AUTO or ON modes, gas or electric heat compatible via DIP switches (also see Thermostat Output section).

I/O Relays All thermostat relays are latching type to minimize power consumption.

Table 4

51M35 Terminal Designations

Terminal Description

R 24VAC

Y1 First-stage cooling

W1 First-stage heating

Y2 Second-stage cooling

W2 Second-stage heating

G Fan control

L Service Indicator

C 24VAC common

Equipment Protection Timers Minimum Compressor OFF time: 5 minutes Minimum Compressor ON time: 4 minutes Minimum Furnace ON time: 3 minutes

Minimum furnace cycle time (elapsed time between any furnace activation and the next furnace activation): 6 min- utes.

Minimum elapsed time between any compressor activa- tion and the next compressor activation: 6 minutes.

NOTE All protection timers (except the compressor OFF timer) can be overridden if a heating or cooling demand is initiated or terminated using the UP, DOWN, HEAT, or COOL buttons.

Equipment Protection Override Both the minimum compressor OFF timer and the mini- mum equipment cycle timer can be overridden by press- ing and holding either the HEAT or COOL button down for 4 seconds.

OverTemperature Protection Thermal-mechanical switch opens W1 and W2 at 93F+/6F.

Filter Reminder Settings of Off, 1, 3, 6 or 12 (months of fan run time) are available. When programmed time has elapsed, a FILTER indicator is displayed.

Page 18

Page 8

505049M 5/1/05

Maintenance Reminder Settings of Off, 6 or 12 (months of chronological time) are available. When programmed time has elapsed, a mainte- nance indicator MAINT" is displayed.

Service Reminder The SERVICE indicator is displayed only under the follow- ing conditions:

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the R terminal;

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the C terminal.

Power Loss/Recovery

Thermostat memory is retained for a minimum of 24 hours during a power loss (includes retention of program infor- mation, HOLD status, programmed temperature setpoint,

IMPORTANT Power must be applied for at least six consecutive hours prior to a power loss in order for memory to be retained for the specified time.

LCD Backlight

Activated for 30 seconds when any button is pressed.

NOTE During an electrical storm or similar disturbance,

the backlight may activate for a few seconds. This is nor-

mal and will no longer occur after the electrical disturbance

has passed.

Thermostat Operating Conditions

35F to 105F, 5% to 90% RH

Thermostat Storage Conditions

40F to 185F, 5% to 95% RH

Thermostat Output Table

Table 5 depicts the 51M35 thermostat output states for var- ious input conditions. The following notes described terms

used in the table.

NOTE X = output is activated with 24VAC.

NOTE The temperature ranges expressed in the follow-

ing definitions of SMALL/LARGE" demands are for guid-

ance only; actual temperatures may vary.

With a small HEAT demand, temperature is: below setpoint 0.5F but above setpoint 1.5F AND 30-minute upstage timer HAS NOT expired.

With a large HEAT demand, temperature is: less than setpoint 1.5F OR 30-minute upstage timer HAS expired.

With a small COOL demand, temperature is: above setpoint +0.5F but below setpoint +1.5F AND 30-minute upstage timer HAS NOT expired.

With a large COOL demand, temperature is: above setpoint +1.5F OR 30-minute upstage timer HAS expired.

Table 5

Thermostat Outputs

Condition W1 W2 Y1 Y2 G

Gas Heat, Auto Fan

HEAT Demand, SMALL X

HEAT Demand, LARGE X X

COOL Demand, SMALL X X

COOL Demand, LARGE X X X

No Demand

Gas Heat, Continuous Fan

HEAT Demand, SMALL X X

HEAT Demand, LARGE X X X

COOL Demand, SMALL X X

COOL Demand, LARGE X X X

No Demand X

Electric Heat, Auto Fan

HEAT Demand, SMALL X X

HEAT Demand, LARGE X X X

COOL Demand, SMALL X X

COOL Demand, LARGE X X X

No Demand

Electric Heat, Continuous Fan

HEAT Demand, SMALL X X

HEAT Demand, LARGE X X X

COOL Demand, SMALL X X

COOL Demand, LARGE X X X

No Demand X

Page 19

05/05 505,048M

Page 1

2005 Lennox Industries Inc. Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE

51M34 Merit Series Thermostat

The Lennox Merit Series 5/2 day programmable electronic thermostat 51M34 provides excellent temperature control and a large, easy-to-read display. This product includes a programmable filter change reminder, an equipment maintenance reminder, and a system check indicator to notify the user when the equipment requires service.

Thermostat 51M34 is suitable for nonheat pump, single- stage heat/single-stage cool applications with either gas or electric furnace.

OPERATION MANUAL

51M34 Merit Series 5/2 Day Programmable Thermostat

CONTROLS 505,048M 05/05 Supersedes 03/05

Table of Contents

51M34 Series Thermostat 1. . . . . . . . . . . . . . . . . . . . . . General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . . Buttons, Backlight, Timers & Settings 2. . . . . . . . . . . . DAY/TIME Set Day and Time 2. . . . . . . . . . . . . . . . . . HEAT Heat Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . COOL Cool Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . HOLD Temperature Hold Mode 4. . . . . . . . . . . . . . . . PROG Thermostat Programming 4. . . . . . . . . . . . . . . FAN Controlling Fan Operation 5. . . . . . . . . . . . . . . . . SETTINGS Filter /Maintenance Reminder 5. . . . . . . Service Indicator 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermostat RESET 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing/Installing Thermostat 6. . . . . . . . . . . . . . . . . Default Thermostat Settings 6. . . . . . . . . . . . . . . . . . . . Technical Specifications 7. . . . . . . . . . . . . . . . . . . . . . . . Thermostat Output Table 8. . . . . . . . . . . . . . . . . . . . . . .

General

These instructions are intended as a general guide and do not supersede local codes in any way. Consult authorities having jurisdiction before installation.

Check equipment for shipping damage. If you find any damage, immediately contact the last carrier.

Introduction

This document describes the operation of Lennox thermostat 51M34. Refer to the installation manual for instructions re- garding installation and wiring of the thermostat.

Initial Thermostat Power-up

When power is initially applied to the thermostat, the dis-

play will appear as shown in figure 1.

FAN ON AUTO

SYSTEM COOL OFF EMG. HEAT

I8:88

88 Figure 1

AM PM

ROOM

MO TU WE TH FR SA SU

SETPOINT

Initial PowerUp Display

SERVICE

FILTER

MAINT

Hi Lo

PROG A | B | C | D HOLD

All display segments are momentarily activated. This oc-

curs as a normal part of thermostat initialization.

Litho U.S.A.

Page 20

Page 2

505048M 5/1/05

Within a few seconds, the Home Screen appears (see fig-

ure 2) with default settings as shown. After about 1 minute

of initialization time, the actual room temperature will be

displayed.

I2:00 PROG A B C D HOLD

FAN ON AUTO

SYSTEM COOL OFF

HEAT70

Home Screen

Figure 2

ROOM

SERVICE

FILTER

MAINT MO TU WE TH FR SA SU

AM PM

NOTE Temperature scale default is Fahrenheit units but

may be reset to show Celsius, if desired. See page 7.

Buttons, Backlight, Timers & Settings

Buttons are located behind the small door on the right hand side of the thermostat (see figure 3).

IMPORTANT Do NOT begin pressing buttons until after you read the following section describing each button.

A pale blue display backlight illuminates for 30 seconds each time any button is pressed.

When PROG or DAY/TIME is pressed, a field begins flash- ing, expecting another input. Start making changes within 15 seconds or the HOME screen will return.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Thermostat Buttons

Figure 3

(DOOR OPEN)

DAY/TIME Setting the Day and Time

Press the DAY/TIME button and set the CURRENT hour, minute, and day of week as follows:

2. Minutes will flash. Use the UP/DOWN arrow button to display the minutes past the hour. Press DAY/TIME.

3. Day MO" (Monday) will flash. Use UP or DOWN arrow buttons to display the current day. Day selections are abbreviated as MO, TU", WE", TH", FR", SA", and SU". Press DAY/TIME.

4. The HOME screen reappears; confirm day and time are correct. This completes day and time setting.

Page 21

Page 3

51M34 SERIES 5/2

HEAT Using the Heat Mode

Enabling and Disabling Heat Mode The thermostat must be in the HEAT mode to control the heating equipment. Press the Heat button to enable or dis- able HEAT mode. If the thermostat is in COOL or OFF mode, pressing the Heat button enables the HEAT mode (indicated by HEAT in the SYSTEM box see figure 4).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Turn Heat ON/OFF

Figure 4

5:30

66 70

HOLD

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM

HEAT

If the thermostat is in heat mode, heat mode is disabled when the HEAT button is pressed. This is indicated by OFF in the SYSTEM box as shown in figure 5.

SYSTEM COOL OFF

HEAT75

Heat/Cool Mode Disabled

Figure 5

ROOM

75 SETPOINT

Heating Demand

SYSTEM COOL OFF

HEAT72 Figure 6

ROOM

75 SETPOINT

Heating Demand

NOTE Heating equipment is activated for at least 3 min- utes if no buttons are pressed during the demand interval.

COOL Using the Cool Mode

Enabling and Disabling Cool Mode

Turn Cool ON/OFF

Figure 7

I0:30

75 70

HOLD

AM PM

SETPOINTROOM

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

FAN

AUTO

SYSTEM COOL

If the thermostat is in cool mode, pressing the Cool button

disables COOL mode (indicated by OFF in the SYSTEM box see figure 5).

Cooling Demand

Set the thermostat to cool mode to control the cooling equipment. Then, if the room temperature is higher than

the temperature setpoint, as shown in figure 8, the thermo- stat detects a cooling demand and will activate the cooling equipment to satisfy the demand.

Cooling Demand

Figure 8

ROOM

70 SETPOINT

SYSTEM COOL OFF

HEAT

Page 22

Page 4

505048M 5/1/05

HOLD Using Temperature Hold Modes

Adjusting Temperature Setpoint in Hold Mode

The temperature setpoint represents the desired tempera- ture of the space around the thermostat. The default tem-

perature setpoint in Hold mode is 70F.

To adjust the setpoint, press the UP or DOWN () arrow buttons (see figure 9); the existing setpoint is displayed to

the right of the actual room temperature. Each button press adjusts the setpoint up or down by 1 degree.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Hold Temperature Mode

Figure 9

I0:36

72 68

HOLD

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM COOL

After the desired setpoint is reached, the HOME screen

will reappear after about 15 seconds.

Permanent Hold Mode

Temporary (2-Hour) Hold

At any time the program is running, from the HOME

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Temporary Hold Temperature Mode

Figure 10

I0:36

72 68

AM PM

SETPOINTROOM

FAN

AUTO

SYSTEM COOL

PROG B HOLD

While in Temporary Hold, press HOLD once to switch to Permanent Hold (HOLD displays solid; PROG not dis- played); press HOLD again to return to the program (PROG displays; HOLD not displayed).

PROG Thermostat Programming

The 51M34 thermostat can be programmed to perform a set of either heating or cooling events (but not a combination of heat and cool) for 5 consecutive days using a set of 4 unique events per day. The remaining 2 days can then be set for a different set of 4 unique events per day. Both the consecutive days and the events/temperature are set by the homeowner.

Change Consecutive days

Figure 11

FILTER MO TU WE TH FR SA SU

To Set Program Events and Temperatures... Figure 12 gives an example of how the two sets of pro- grams can be set for a normal workweek and weekend.

Figure 12

5/2 Program Example

5DAY PROGRAM:

| A | B | C | D |

2DAY PROGRAM:

| A | B | C | D |

6AM NOON 6PM MID 6AM NIGHT

NOTE Pressing ENTER during the following program- ming steps, saves and exits to the HOME screen.

To program events and temperatures, perform the follow- ing steps, once with Cool selected and once with Heat se- lected.

1. Press and release PROG. AM 6:00", period A", and the 5 consecutive days are displayed; AM 6" flashes.

2. Use the Up/Down arrow buttons to select the desired hour; press PROG when the desired hour is reached.

3. Use the Up/Down arrow buttons to select the desired minute; press PROG.

4. Use the Up/Down arrow buttons to select the desired temperature setpoint; press PROG.

5. Repeat steps 2 through 4 for periods B, C, and D.

6. Repeat steps 1 through 5 for the 2day program.

Page 23

Page 5

51M34 SERIES 5/2

FAN Controlling the Fan Operation

Use the FAN button to select either continuous fan mode or auto fan mode.

To change from continuous to auto fan mode (or vice ver- sa), press the FAN button. Note whether a fan icon in the FAN box is present (indicating that the fan is running) or not (fan not running).

If continuous fan mode is enabled (ON displayed in FAN box see figure 13), the fan will run continuously regard- less of whether the heating or cooling equipment is run- ning.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Using Fan ON

Figure 13

I0:I0

PROG B

AM PM

ROOM

FAN ON

SYSTEM

HEAT

If auto fan mode is selected (AUTO displayed in FAN box see figure 14), the fan will only run when the heating or cooling equipment is running.

Heat

Prog

Fan

Settings

Cool

Hold

Enter

Day/Time

Using Fan Auto

Figure 14

I0:36

AM PM

ROOM

FAN

AUTO

SYSTEM COOL

PROG B

SETTINGS Filter/Maintenance Reminders

The 51M34 thermostat is designed to remind you when the filter needs changing or when routine maintenance is re- quired, as (and if) defined, by you. These optional remind- ers are not enabled until you activate them. To do so, press the Settings button (shown below the Fan button in figure 14) once or twice for the desired reminder as shown in fig- ure 15 and as described in table 1.

Reminder Settings Display

Figure 15

FILTER

OFF MAINT

For FILTER, press Settings button 1 time

For MAINT, press Settings button 2 times

The default setting for the reminders is OFF (disabled). Press Up/Down arrow buttons to select the desired re- minder intervals.

Table 1

Filter and Maintenance Reminders

Buttons to Use Reminder

Available Settings and How to Use

Settings (1st press)

FILTER Total fan run time expressed in months (Off 1 3 6 12); for

then Arrows to scroll

, , , , example, if fan runs 12 hours a day 1 month reminder displays

selections ,

in 2 calendar months.

Settings (2nd press)

MAINT Elapsed chronological time in months (Off 6 12) Use this

then Arrows to scroll

, , . , for example, to remind yourself when to perform routine checks

selections

or when to call a technician for perodic preventive maintenance.

Enter Stores settings.

NOTE The HOME screen will reappear about 15 seconds after the final arrow button press. OR, press ENTER at any time to store any changes and exit to the HOME screen.

After either programmed interval has elapsed, the remind- er will be displayed as shown in figure 16.

I0:i2 PROG A B C D HOLD

FAN ON AUTO

SYSTEM COOL OFF

HEAT78

Reminders

Figure 16

ROOM

SERVICE

FILTER

AM PM

MO TU WE TH FR SA SU MAINT

After the filter has been changed, reset the filter reminder by pressing the SETTINGS button for 4 seconds. The

screen will blink for a few moments to indicate that the tim- er has been reset.

Page 24

Page 6

505048M 5/1/05

Service Indicator

When abnormal equipment operation is detected, the SERVICE indicator will flash on the screen (see figure 17).

This indicates that the equipment requires service from a qualified service technician.

I0:i4 PROG A B C D HOLD

Service Indicator Flashing

Figure 17

ROOM

SERVICE

FILTER

AM PM

FAN ON AUTO

SYSTEM COOL OFF

HEAT

MO TU WE TH FR SA SU

Thermostat RESET

CAUTION When the RESET button is pressed, ALL settings re- vert back to the defaults, including the default pro- gram (see tables 2 and 3).

Removing/Installing Thermostat

The thermostat hinges on tabs on the top of the subbase;

no tool is needed to remove the thermostat from the sub- base. Pivot the bottom of the thermostat outward (releas- ing the snaps), then lift up to remove.

To replace it, first position the top tilted toward the wall bracket and align it until you feel the tabs and slots engage; then, while the top is in place, pivot the bottom toward the

wall until the thermostat snaps into place.

Default Thermostat Settings

Default thermostat settings are in table 2 and the default program is shown in table 3.

Table 2

Default Thermostat Settings

Mode Heat (Permanent Hold Mode)

Setpoint 70F (or 21C)

Fan Auto

Filter Reminder OFF

Maintenance Reminder OFF

Equipment Protection Timers

Reset Back to Zero

Table 3

Default Program Settings

Programs Time Temperature (Heat)

Temperature (Cool)

Thursday, Friday

Weekend Saturday, Sunday

Page 25

Page 7

51M34 SERIES 5/2

Technical Specifications

Thermostat Type

Electronic programmable thermostat for 1-Stage- Heat/1-Stage Cool, gas or electric heat, nonheat pump,

nonpower robbing applications.

Power Supply Range

18VAC 30VAC (24VAC nominal), 60Hz

CAUTION 24VAC is present on the terminals of the thermostat bracket. If removing the thermostat from the wall, use caution and avoid touching any of the connec- tor terminals on the wall bracket.

Also, when working with the thermostat dip switches, use a nonconductive tool and take cau- tion to avoid making any contact with the circuit board, its imprinted circuitry and its connector prongs.

Temperature Display

Display Scale: Fahrenheit or Celsius user selectable (via

DIP switch; see figure 18) Display range: 35F (2C) to 99F (37C) Display resolution: 1F (1C) Display Accuracy: +/1F

If the Fahrenheit/Celsius display must be changed, use a

plastic, nonconductive tool to push the dip switch to the right position (see figure 18).

F/C (Fahrenheit/Celsius) switch shown in Celsius position

Figure 18

Changing Fahrenheit/Celsius Setting

6 PLUG IN (Use Care To Avoid Bending Prongs.)

Temperature Measurement Range

Measurement Scale: Fahrenheit Measurement Range: 35F to 99F Measurement Resolution: 0.5F Measurement Accuracy: +/1F

Field Offset: via DIP switches to +/3F Sampling Method: temperature measurements sampled every 15 seconds. Displayed temperature is the average of the last four measurements.

Temperature Setpoint Range Setting range: 50F (10C) to 90F (32C) Setting resolution: 1F (1C)

Fan Control AUTO or ON modes, gas or electric heat compatible via DIP switches (also see Thermostat Output section).

I/O Relays All thermostat relays are latching type to minimize power consumption.

Table 4

51M34 Terminal Designations

Terminal Description

R 24VAC

Y1 First stage cooling

W1 First stage heating

G Fan control

L Service Indicator

C 24VAC common

Equipment Protection Timers Minimum Compressor OFF time: 5 minutes Minimum Compressor ON time: 4 minutes Minimum Furnace ON time: 3 minutes

Minimum furnace cycle time (elapsed time between any furnace activation and the next furnace activation): 6 min- utes.

Minimum elapsed time between any compressor activa- tion and the next compressor activation: 6 minutes.

NOTE All protection timers (except the compressor OFF timer) can be overridden if a heating or cooling demand is initiated or terminated using the UP, DOWN, HEAT, or COOL buttons.

OverTemperature Protection Thermal-mechanical switch opens W1 at 93F+/6F.

Filter Reminder Settings of Off, 1, 3, 6 or 12 (months of fan run time) are available. When programmed time has elapsed, a FILTER indicator is displayed.

Page 26

Page 8

505048M 5/1/05

Maintenance Reminder Settings of Off, 6 or 12 (months of chronological time) are available. When programmed time has elapsed, a mainte- nance indicator MAINT" is displayed.

Service Reminder The SERVICE indicator is displayed only under the follow- ing conditions:

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the R terminal;

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the C terminal.

Power Loss/Recovery Thermostat memory is retained for a minimum of 24 hours during a power loss (includes retention of program infor-

mation, HOLD status, programmed temperature setpoint, heat/cool and fan mode settings, filter reminder status, maintenance reminder status, and equipment protection timers). After 24 hours of power loss, programmed settings will be lost and replaced with default settings.

IMPORTANT Power must be applied for at least six consecutive hours prior to a power loss in order for memory to be retained for the specified time.

LCD Backlight Activated for 30 seconds when any button is pressed.

NOTE During an electrical storm or similar disturbance,

the backlight may activate for a few seconds. This is nor-

mal and will no longer occur after the electrical disturbance

has passed.

Thermostat Operating Conditions

35F to 105F, 5% to 90% RH

Thermostat Storage Conditions

40F to 185F, 5% to 95% RH

Thermostat Output Table

Table 5 depicts the 51M34 thermostat output states for var-

ious input conditions.

Table 5

Thermostat Outputs

Condition W1 Y1 G

Gas Heat, Auto Fan

HEAT Demand X

COOL Demand X X

No Demand

Gas Heat, Continuous Fan

HEAT Demand X X

COOL Demand X X

No Demand X

Electric Heat, Auto Fan

HEAT Demand X X

COOL Demand X X

No Demand

Electric Heat, Continuous Fan

HEAT Demand X X

COOL Demand X X

No Demand X

NOTE X = output is activated with 24VAC.

Page 27

07/05 505,068M

Page 1

2005 Lennox Industries Inc. Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE

51M39 Merit Series Thermostat

The Lennox Merit Series 7 day programmable electronic

thermostat 51M39 provides excellent temperature control

and a large, easy-to-read display. This product includes a

programmable filter change reminder, an equipment

maintenance reminder, and a system check indicator to

notify the user when the equipment requires service.

Thermostat 51M39 is suitable for non-heat pump, two-

stage heat/two-stage cool applications using a gas or elec-

tric furnace. Also, the thermostat provides autochange-

over capability.

OPERATION MANUAL

51M39 Merit Series 7 Day Programmable Thermostat

CONTROLS 505,068M 07/05

Table of Contents

51M39 Series Thermostat 1. . . . . . . . . . . . . . . . . . . . . . General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . . Buttons, Backlight, Timers & Settings 2. . . . . . . . . . . . DAY/TIME Set Day and Time 2. . . . . . . . . . . . . . . . . . HEAT Heat Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . COOL Cool Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . AUTO Using the Autochangeover Mode 4. . . . . . . . . HOLD Temperature Hold Mode 4. . . . . . . . . . . . . . . . PROG Thermostat Programming 4. . . . . . . . . . . . . . . COPY Copy a Program 6. . . . . . . . . . . . . . . . . . . . . . . FAN Controlling Fan Operation 5. . . . . . . . . . . . . . . . . Displaying Outside Temperature 6. . . . . . . . . . . . . . . . . SETTINGS Filter /Maintenance Reminder 6. . . . . . . Service Indicator 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermostat RESET 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing/Installing Thermostat 7. . . . . . . . . . . . . . . . . Default Thermostat Settings 7. . . . . . . . . . . . . . . . . . . . Thermostat Output Table 7. . . . . . . . . . . . . . . . . . . . . . . Technical Specifications 8. . . . . . . . . . . . . . . . . . . . . . . .

General

These instructions are intended as a general guide and do

not supersede local codes in any way. Consult authorities

having jurisdiction before installation.

Check equipment for shipping damage. If you find any

damage, immediately contact the last carrier.

Introduction

This document describes the operation of Lennox thermo-

stat 51M39. Refer to the installation manual for instructions

regarding installation and wiring of the thermostat.

Initial Thermostat Power-up

When power is initially applied to the thermostat, the dis-

play will appear as shown in figure 1.

HEAT SETPOINT

COOL

OFF

AUTO

EMG.

HEAT

I8:88

i88 Figure 1

AM PM

OUTROOM

MO TU WE TH FR SA SU

COOL SETPOINT

Initial PowerUp Display

FILTER

MAINTENANCE

Hi Lo

FAN ON AUTO

SERVICE

Copy tofrom

PROG A B C D

HOLD

All display segments are momentarily activated. This oc-

curs as a normal part of thermostat initialization.

Litho U.S.A.

Page 28

Page 2

505068M 07/05

Within a few seconds, the HOME screen appears (see fig-

ure 2) with default settings as shown. After about 1 minute

of initialization time, the actual room temperature will be

displayed.

NOTE Tables 2 and 3 on page 7 show all system and

programming defaults.

COOL

OFF

AUTO

EMG.

HEAT

I0:26 PROG A B C D HOLD

FAN ON AUTO

HOME Screen

Figure 2

ROOM

AM PM

At this point, the thermostat will be fully functional; its de-

fault temperature setpoint (not shown) is 70F. At this

point, if the equipment has been fully powered and if a heat

demand were present, the system would begin operating.

NOTE Temperature scale default is Fahrenheit units but

may be reset to show Celsius, if desired. See page 8.

Buttons, Backlight, Timers & Settings

Buttons are located behind the small door on the right

hand side of the thermostat (see figure 3).

IMPORTANT Do NOT begin pressing buttons until after you read the following section describing each button.

A pale blue display backlight illuminates for 30 seconds

each time any button is pressed.

When PROG or DAY/TIME button is pressed, a field be-

gins flashing, expecting another input. Start making

changes within 15 seconds or the HOME screen will re-

turn.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Thermostat Buttons

Figure 3

(DOOR OPEN)

Auto

Copy

(Outside)

When an Arrow, HOLD, HEAT, or COOL button is pressed,

SETPOINT and the temperature setting appears for 15

seconds. If desired, start making changes within 15 sec-

onds or the HOME screen will return. The backlight will

turn off 15 seconds after the HOME screen reappears.

DAY/TIME Setting the Day and Time

Press the DAY/TIME button and set the CURRENT hour,

minute, and day of week as follows:

1. AM12" will flash on the screen. Press the UP/DOWN arrows to change the hour. (AM" or PM" must corre- spond to time of day.) Press DAY/TIME OR, if adjust- ing for daylight savings time, pressing the ENTER but- ton stores the single change and exits to the HOME screen, bypassing minutes and day of week.

2. Minutes will flash. Use the UP/DOWN arrow button to display the minutes past the hour. Press DAY/TIME.

3. Day MO" (Monday) will flash. Use UP or DOWN arrow buttons to display the current day. Day selections are abbreviated as MO, TU", WE", TH", FR", SA", and SU". Press DAY/TIME.

4. The HOME screen reappears; confirm day and time are correct. This completes day and time setting.

Page 29

Page 3

51M39 SERIES 5/2

HEAT Using the Heat Mode

Enabling and Disabling Heat Mode

The thermostat must be in the heat mode to control the

heating equipment. Press the HEAT button to enable or

disable HEAT mode. If the thermostat is in cool or off

mode, pressing the HEAT button enables the heat mode

(indicated by HEAT in the lower right corner see figure 4).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Turn Heat ON/OFF

Figure 4

(DOOR OPEN)

Auto

Copy

(Outside)

5:30

If the thermostat is in heat mode, heat mode is disabled

when the HEAT button is pressed. This is indicated by OFF

near the right side of the display as shown in figure 5.

Heat/Cool Mode Disabled

Figure 5

ROOM

75 HEAT SETPOINT

OFF

Heating Demand

Set the thermostat to heat mode to control the heating

equipment. Then, if the room temperature is lower than the

temperature setpoint, as shown in figure 6, the thermostat

detects a heating demand and will activate the heating

equipment to satisfy the demand.

Heating Demand

Figure 6

ROOM

75 HEAT SETPOINT

HEAT

Heating operation is indicated by a flame icon in the lower

right corner. When the actual temperature rises above the

temperature setpoint, the flame icon will disappear. This

indicates that the heating demand has been satisfied and

that the heating equipment has been turned off.

If your system supports 2stage heating (as does the

51M39 thermostat), you may notice various heating levels

being delivered during a demand.

NOTE Heating equipment is activated for at least 3 min- utes if no buttons are pressed during the demand interval.

COOL Using the Cool Mode

Enabling and Disabling Cool Mode

Use the COOL button to enable or disable cool mode as

desired. If the thermostat is in heat or off mode, cool mode

is enabled when the COOL button is pressed. This is indi-

cated by COOL on the right side of the display (see figure

8).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Turn Cool ON/OFF

Figure 7

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

If the thermostat is in cool mode, pressing the COOL but-

ton disables cool mode (indicated by OFF in the SYSTEM

box see figure 5).

Cooling Demand

Set the thermostat to cool mode to control the cooling

equipment. Then, if the room temperature is higher than

the temperature setpoint, as shown in figure 7, the thermo-

stat detects a cooling demand and will activate the cooling

equipment to satisfy the demand.

Cooling operation is indicated by flashing snowflake"

icons on the right side of the display. When the actual tem-

perature drops below the temperature setpoint, the snow-

flake icons will disappear. This indicates that the cooling

demand has been satisfied and that the cooling equipment

has been turned off.

If your system supports 2stage cooling (as does the

51M39 thermostat), you may notice various cooling levels

being delivered during a demand. Also, if a small cooling

demand is present, "Lo" will be displayed in the SYSTEM

box. However, if a large cooling demand is present, "Hi" will

be displayed in the lower right corner (shown in figure 8).

Cooling Demand

Figure 8

ROOM

Hi Lo

FAN AUTO

COOL76

68 HEAT SETPOINT

COOL SETPOINT

Page 30

Page 4

505068M 07/05

NOTE If no buttons are pressed during a demand for

cooling, the equipment must operate for at least 4 minutes.

After a demand has been satisfied, cooling equipment op-

eration is locked out for 5 minutes. If another cooling de-

mand occurs during this 5minute interval, COOL" and the

snowflakes will flash; however, the cooling equipment will

not operate until the 5minute delay has elapsed.

AUTO Using the Autochangeover Mode

When in either heat mode or cool mode, autochangeover can be enabled or disabled by pressing the AUTO button. If enabled, AUTO appears at the lower right corner of the dis- play. The thermostat will then automatically change over from heating to cooling and vice versa, to keep the room

temperature in between the heating and cooling setpoints. Autochangeover can be used in either of the thermostat hold modes, or when the thermostat program is running. These modes are described later.

HOLD Using Temperature Hold Modes

When HOLD is displayed at the HOME screen, the ther-

mostat is in a temperature hold condition. This means that

the temperature program data is ignored and the thermo-

stat functions much like a nonprogrammable thermostat.

Adjusting Temperature Setpoint in Hold Mode

The temperature setpoint represents the desired tempera- ture of the space around the thermostat. The default heat setpoint in hold mode is 70F; the default cool setpoint in hold mode is 78F.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Hold Temperature Mode

Figure 9

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

To adjust the setpoint, press the UP or DOWN () arrow

buttons; the existing setpoint is displayed to the right of the

actual room temperature. Each button press adjusts the

setpoint up or down by 1 degree.

After the desired setpoint is reached, the HOME screen

will reappear after about 15 seconds.

Permanent Hold Mode At any time the program is running, from the HOME

screen, set a permanent hold (program override) by press-

ing the HOLD button (see figure 9). The thermostat now

functions much like a nonprogrammable thermostat. Use

the Up/Down arrow buttons to adjust the hold setpoint. To

return to the program, press the HOLD button again.

Temporary (2-Hour) Hold At any time the program is running, from the HOME

screen, set a temporary 2-hour hold by pressing the Up/

Down arrow buttons until the desired setpoint is displayed;

HOLD" flashes (see figure 10). This overrides the pro-

gram for 2 hours from the last button press, then returns to

the program.

While in Temporary Hold, press the HOLD button once to

switch to Permanent Hold (HOLD displays solid; PROG

not displayed); press the HOLD button again to return to

the program (PROG displays; HOLD not displayed).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Temporary Hold Temperature Mode

Figure 10

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

PROG Thermostat Programming

The 51M39 thermostat can be programmed to perform a set of both heating and cooling events for each day of the week. Each day can be programmed for 4 unique events per day, and each day can be different from any other day.

To Set Program Events and Temperatures Figure 11 gives an example of how up to 7 different pro- grams can be set. Programs A and C reflect the desired warmth while the home IS occupied (72); B allows less heating while the home is NOT occupied; D reflects a cool sleeping temperature.

NOTE This example shows heat setpoints; a similar pro-

gram may be set for cool setpoints.

Page 31

Page 5

51M39 SERIES 5/2

Figure 11

Program Example

6AM NOON 6PM MID 6AM NIGHT

B D

B C

A B C

A B

C D

SATURDAY PROGRAM: 72

SUNDAY PROGRAM: 72

FRIDAY PROGRAM: 72

THURSDAY PROGRAM: 72

WEDNESDAY PROGRAM: 72

TUESDAY PROGRAM: 72

MONDAY PROGRAM: 72

NOTE Pressing the ENTER button during the following programming steps, saves and exits to the HOME screen.

To program events and temperatures, perform the follow- ing steps.

1. Press and release the PROG button. "MO" (Monday), "AM 6:00", period "A", "COOL SETPOINT 78", and "HEAT SETPOINT 70" are displayed. "AM 6" flashes.

2. Use the Up/Down arrow buttons to select the desired hour; press the PROG button when the desired hour is reached; use the Up/Down arrow buttons again to select desired minute. The selected hour/minute is when the program will start. Press the PROG button.

3. Use the Up/Down arrow buttons to select the desired heat setpoint; press the PROG button.

4. Use the Up/Down arrow buttons to select the desired cool setpoint; press the PROG button.

5. Repeat steps 1 4 for Monday, periods B, C, and D.

6. COPY A PROGRAM If the program entered for Monday is satisfactory for other days of the week, do the following to repeat the same program for other days:

A Press the PROG button, then press the COPY button. The display clears the screen except for Copy from MO with MO" flashing. Press the COPY button again to copy Mondays program.

B The display changes to Copy to MO". Use the ar- row buttons to scroll to the desired day where you want the same program as Monday. Press the COPY button.

C Repeat steps A and B for as many days as you want the same program.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Copy a Programmed Day to Another Day

Figure 12

(DOOR OPEN)

Auto

Copy

(outside)

Copy from MO

7. Repeat steps 1 5 to program different times and tem- peratures for days not yet programmed.

FAN Controlling the Fan Operation

Use the FAN button to select either continuous fan mode or auto fan mode.

To change from continuous to auto fan mode (or vice ver- sa), press the FAN button. Note whether a fan icon in the

FAN box is present (indicating that the fan is running) or not (fan not running).

If continuous fan mode is enabled (ON displayed in FAN box see figure 13), the fan will run continuously regard- less of whether the heating or cooling equipment is run- ning.

Using Fan ON

Figure 13

Heat

Prog

Fan

Cool

Day/Time

Hold

Auto

Copy

i0:30

If auto fan mode is selected (AUTO displayed in FAN box see figure 14), the fan will only run when the heating or cooling equipment is running.

Using Fan AUTO

Figure 14

Heat

Prog

Fan

Cool

Day/Time

Hold

Auto

Copy

i0:30

Page 32

Page 6

505068M 07/05

Displaying Outside Temperature

Pressing the ENTER (Outside) button at the HOME screen displays the outside temperature (see figure 15) for several seconds, then returns to room temperature.

Check Outside Temperature

Figure 15

88 Fan

Settings

Hold

Enter

(Outside)

SETTINGS Filter/Maintenance Reminders

The 51M39 thermostat is designed to remind you when the

filter needs changing or when routine maintenance is re-

quired, as (and if) defined, by you. These optional remind-

ers are not enabled until you activate them. To do so, press

the SETTINGS button once or twice for the desired re-

minder as shown in figure 16 and as described in table 1.

Reminder Settings Display

Figure 16

FILTER

OFF

MAINTENANCE

For FILTER, press SETTINGS button 1 time

For MAINTENANCE, press SETTINGS button 2 times

The default setting for the reminders is OFF (disabled).

Press Up/Down arrow buttons to select the desired re-

minder intervals.

Table 1

Filter and Maintenance Reminders

Buttons to Use Reminder

Available Settings and How to Use

Settings (1st press)

FILTER Total fan run time expressed in months (Off 1 3 6 12); for

then Arrows to scroll

, , , , example, if fan runs 12 hours a day, 1 month reminder displays in 2

selections

calendar months.

Settings (2nd press)

then Arrows

MAINTE- NANCE

Elapsed chronological time in months (Off, 6, 12). Use this, for example, to remind yourself when to

to scroll selections

perform routine checks or when to call a technician for perodic preventive maintenance.

Enter Stores settings.

NOTE The HOME screen will reappear about 15 seconds after the final arrow button press. OR, press the ENTER button at any time to store any changes and exit to the HOME screen.

After either programmed interval has elapsed, the remind-

er will be displayed as shown in figure 17.

COOL

OFF

AUTO

EMG.

HEAT

I0:26 PROG A B C D HOLD

FAN ON AUTO FILTER SERVICE

MAINTENANCE

Reminders

Figure 17

ROOM

AM PM

COOL

OFF

AUTO

EMG.

HEAT

FAN ON AUTO FILTER SERVICE

MAINTENANCE

Service Indicator FlashingROOM

Filter & Maintenance

Indicators

After the filter has been changed or maintenance per-

formed, reset the reminder by pressing the SETTINGS

button for 4 seconds at the corresponding reminder set-

tings screen. The screen will blink for a few moments to in-

dicate that the timer has been reset.

Service Indicator

When abnormal equipment operation is detected, the

SERVICE indicator will flash on the screen (see figure 17).

This indicates that the equipment requires service from a

qualified service technician.

Thermostat RESET

Under some abnormal conditions, it may be necessary to

reset" the thermostat to its default condition. Such a RE-

SET would delete all programming and settings and there-

fore should only be used on rare occasions when the the

thermostat fails to function as designed and/or as pro-

grammed. Such an instance can occur as a result of a pow-

er surge or similar electrical disturbance (e.g. after an elec-

trical storm or power outage). The RESET button can be

used to recover from this situation.

CAUTION When the RESET button is pressed, ALL settings re- vert back to the defaults, including the default pro- gram (see tables 2 and 3).

The RESET button is an unlabeled, recessed button lo-

cated behind the door on the righthand side of the thermo-

stat, below the SETTINGS button (see figure 3). Use a pa-

per clip or small pencil to press the RESET button; ALL

thermostat settings will be reset to the defaults listed in the

Default Thermostat Settings section.

Page 33

Page 7

51M39 SERIES 5/2

Removing and Installing Thermostat

The thermostat hinges on tabs on the top of the subbase;

no tool is needed to remove the thermostat from the sub-

base. Pivot the bottom of the thermostat outward (releas-

ing the snaps), then lift up to remove.

To install it, first position the top tilted toward the wall brack-

et and align it until you feel the tabs and slots engage; then,

while the top is in place, pivot the bottom toward the wall

until the thermostat snaps into place.

Default Thermostat Settings

Default thermostat settings are in table 2 and the default

program is shown in table 3.

Table 2

Default Thermostat Settings

Mode Heat (Perm. Hold)

Heat Setpoint (Perm Hold) 70F (or 21C)

Cool Setpoint (Perm Hold) 78F (or 26C)

Fan Auto

Filter Reminder OFF

Maintenance Reminder OFF

Equipment Protection Timers Reset Back to Zero

Autochangeover OFF

Table 3

Default Program Settings (Time & Temp.)

Programs Time Temp. Heat Temp. Cool

All days A 6:00am 70F / 21C 78F / 26C All days B 8:00am 62F / 17C 85F / 29C All days C 6:00pm 70F / 21C 78F / 26C All days D 10:00pm 62F / 17C 82F / 28C

Thermostat Output Table

Table 4 depicts the 51M39 thermostat output states for var-

ious input conditions. The following notes described terms

used in the table.

Table 4

Thermostat Outputs

Condition W1 W2 Y1 Y2 G

Gas Heat, Auto Fan

Heat Demand, SMALL X

Heat Demand, LARGE X X

Cool Demand, SMALL X X

Cool Demand, LARGE X X X

No Demand

Gas Heat, Continuous Fan

Heat Demand, SMALL X X

Heat Demand, LARGE X X X

Cool Demand, SMALL X X

Cool Demand, LARGE X X X

No Demand X

Electric Heat, Auto Fan

Heat Demand, SMALL X X

Heat Demand, LARGE X X X

Cool Demand, SMALL X X

Cool Demand, LARGE X X X

No Demand

Electric Heat, Continuous Fan

Heat Demand, SMALL X X

Heat Demand, LARGE X X X

Cool Demand, SMALL X X

Cool Demand, LARGE X X X

No Demand X

NOTE X = output is activated with 24VAC.

NOTE The temperature ranges expressed in the follow- ing definitions of SMALL/LARGE" demands are for guid- ance only; actual temperatures may vary.

With a SMALL heat demand, temperature is: below setpoint 0.5F but above setpoint 1.5F AND 30-minute upstage timer HAS NOT expired.

With a LARGE heat demand, temperature is: less than setpoint 1.5F OR 30-minute upstage timer HAS expired.

With a SMALL cool demand, temperature is: above setpoint +0.5F but below setpoint +1.5F AND 30-minute upstage timer HAS NOT expired.

With a LARGE cool demand, temperature is:

above setpoint +1.5F OR 30-minute upstage timer HAS expired.

Page 34

Page 8

505068M 07/05

Technical Specifications

Thermostat Type

Electronic programmable thermostat for 2Stage (gas or

electric) Heat/2-Stage Cool, nonheat pump, nonpower

robbing applications.

Table 5

51M39 Terminal Designations

Terminal Description

R 24VAC

Y1 First-stage cooling

W1 First-stage heating

Y2 Second-stage cooling

W2 Second-stage heating

G Fan control

L Service Indicator

C 24VAC common

T Outdoor temperature sensor connection 1

T Outdoor temperature sensor connection 2

Power Supply Range

18VAC 30VAC (24VAC nominal), 60Hz

CAUTION 24VAC is present on the terminals of the thermostat bracket. If removing the thermostat from the wall, use caution and avoid touching any of the connec- tor terminals on the wall bracket.

Also, when working with the thermostat dip switches, use a nonconductive tool and take cau- tion to avoid making any contact with the circuit board, its imprinted circuitry and its connector prongs.

Temperature Display

Display Scale: Fahrenheit or Celsius user selectable (via

DIP switch; see figure 18)

F/C (Fahrenheit/Celsius) switch shown in Celsius position

Figure 18

Changing Fahrenheit/Celsius Setting

PLUG IN (Use Care To Avoid Bending Prongs.)

Display range: 35F (2C) to 99F (37C)

Display resolution: 1F (1C)

Display Accuracy: +/1F

If the Fahrenheit/Celsius display must be changed, use a

plastic, nonconductive tool to push the dip switch to the

right position (see figure 18).

Indoor Temperature Measurement Range Measurement Scale: Fahrenheit

Measurement Range: 35F to 99F

Measurement Resolution: 0.5F

Measurement Accuracy: +/1F

Field Offset: via DIP switches to +/3F

Sampling Method: temperature measurements sampled

every 15 seconds. Displayed temperature is the average

of the last four measurements.

Outdoor Temperature Measurement Range Measurement Scale: Fahrenheit

Measurement Range: 22F to 122F

Measurement Resolution: 1F

Measurement Accuracy: +/2F

Temperature Setpoint Range Setting range: 50F (10C) to 90F (32C)

Setting resolution: 1F (1C)

Smart Setback Recovery (via DIP switch #6) Smart Setback Recovery (SSR) affects the way the ther-

mostat responds to program events. If SSR is disabled, the

thermostat will react to a program event at the time the

event occurs. However, if SSR is enabled, the thermostat

will react to a program event before the event occurs such

that the desired temperature is reached at the time of the

event, not after.

Autochangeover Deadband Selection (via DIP switch #7) Autochangeover deadband can be set to 4 or 6 degrees.

When autochangeover is enabled (via the AUTO button),

the thermostat will automatically change over from heating

to cooling and vice versa, to keep the room temperature in

between the heating and cooling setpoints. The deadband

is the minimum difference between the heating and cooling

setpoints.

Fan Control AUTO or ON modes, gas or electric heat compatible via

DIP switches (also see Thermostat Output section).

I/O Relays All thermostat relays are latching type to minimize power

consumption.

Equipment Protection Timers Minimum Compressor OFF time: 5 minutes

Minimum Compressor ON time: 4 minutes

Minimum Furnace ON time: 3 minutes

Minimum furnace cycle time (elapsed time between any

furnace activation and the next furnace activation): 6 min-

utes.

Minimum elapsed time between any compressor activa-

tion and the next compressor activation: 6 minutes.

Page 35

Page 9

51M39 SERIES 5/2

NOTE All protection timers (except the compressor OFF timer) can be overridden if a heating or cooling demand is initiated or terminated using the UP, DOWN, HEAT, or COOL buttons.

Equipment Protection Override

Both the minimum compressor OFF timer and the mini-

mum equipment cycle timer can be overridden by press-

ing and holding either the HEAT or COOL button down for 4

seconds.

OverTemperature Protection

Thermal-mechanical switch opens W1 and W2 at

93F+/6F.

Filter Reminder

Settings of Off, 1, 3, 6 or 12 (months of fan run time) are

available. When programmed time has elapsed, a FILTER

indicator is displayed.

Maintenance Reminder

Settings of Off, 6 or 12 (months of chronological time) are

available. When programmed time has elapsed, a mainte-

nance indicator MAINTENANCE" is displayed.

Service Reminder

The SERVICE indicator is displayed only under the follow-

ing conditions:

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the R terminal;

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the C terminal.

Power Loss/Recovery

Thermostat memory is retained for a minimum of 24 hours during a power loss (includes retention of clock setting, program information, HOLD status, programmed temper- ature setpoint, heat/cool and fan mode settings, filter re- minder status, maintenance reminder status, and equip- ment protection timers). After 24 hours of power loss, programmed settings will be lost and replaced with default

settings.

IMPORTANT Power must be applied for at least six consecutive hours prior to a power loss in order for memory to be retained for the specified time.

LCD Backlight

Activated for 30 seconds when any button is pressed.

NOTE During an electrical storm or similar disturbance,

the backlight may activate for a few seconds. This is nor-

mal and will no longer occur after the electrical disturbance

has passed.

Thermostat Operating Conditions

35F to 105F, 5% to 90% RH

Thermostat Storage Conditions

40F to 185F, 5% to 95% RH

Page 37

07/05 505,069M

Page 1

2005 Lennox Industries Inc. Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE

51M42 Merit Series Thermostat

The Lennox Merit Series 7day programmable electronic thermostat 51M42 provides excellent temperature control

and a large, easy-to-read display. It includes a programmable filter change reminder, an equipment maintenance reminder, and a system check indicator to notify the user when the equipment requires service.

Thermostat 51M42 is suitable for heat pump, three-stage heat/two-stage cool applications using a gas or electric auxiliary heat source. In addition to displaying outdoor temperature, the outdoor temperature sensor provides auxiliary heat lockout, balance point operation, and dual fuel compatibility. Also, the thermostat provides auto-

changeover capability.

OPERATION MANUAL

51M42 Merit Series 7Day Programmable Thermostat

CONTROLS 505,069M 07/05

Table of Contents

51M42 Series Thermostat 1. . . . . . . . . . . . . . . . . . . . . . General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . . Buttons, Backlight, Timers & Settings 2. . . . . . . . . . . . DAY/TIME Set Day and Time 2. . . . . . . . . . . . . . . . . . HEAT Heat Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . COOL Cool Mode 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . AUTO Using the Autochangeover Mode 4. . . . . . . . . HOLD Temperature Hold Mode 4. . . . . . . . . . . . . . . . PROG Thermostat Programming 5. . . . . . . . . . . . . . . COPY Copy a Program 5. . . . . . . . . . . . . . . . . . . . . . . FAN Controlling Fan Operation 6. . . . . . . . . . . . . . . . . Displaying Outside Temperature 6. . . . . . . . . . . . . . . . . SETTINGS Filter and Maintenance Reminders 6. . . SETTINGS Balance Point 7. . . . . . . . . . . . . . . . . . . . . Service Indicator 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermostat RESET 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing/Installing Thermostat 7. . . . . . . . . . . . . . . . . Default Thermostat Settings 7. . . . . . . . . . . . . . . . . . . . Technical Specifications 9. . . . . . . . . . . . . . . . . . . . . . . . Thermostat Output Table 8. . . . . . . . . . . . . . . . . . . . . . .

General

These instructions are intended as a general guide and do not supersede local codes in any way. Consult authorities having jurisdiction before installation.

Check equipment for shipping damage. If you find any damage, immediately contact the last carrier.

Introduction

This document describes the operation of Lennox thermostat

51M42. Refer to the installation manual for instructions re- garding installation and wiring of the thermostat.

Initial Thermostat Power-up

When power is initially applied to the thermostat, the dis- play will appear as shown in figure 1.

HEAT SETPOINT

COOL

OFF

AUTO

EMG.

HEAT

I8:88

i88 Figure 1

AM PM

OUTROOM

MO TU WE TH FR SA SU

COOL SETPOINT

Initial PowerUp Display

FILTER

MAINTENANCE

Hi Lo

FAN ON AUTO

SERVICE

Copy tofrom

PROG A B C D

HOLD

All display segments are momentarily activated. This oc- curs as a normal part of thermostat initialization.

Litho U.S.A.

Page 38

Page 2

505069M 07/05

Within a few seconds, the HOME screen appears (see fig- ure 2) with default settings as shown. After about 1 minute of initialization time, the actual room temperature will be displayed.

NOTE Tables 2 and 3 on page 8 show all system and

programming defaults.

COOL

OFF

AUTO

EMG.

HEAT

I0:26 PROG A B C D HOLD

FAN ON AUTO

HOME Screen

Figure 2

ROOM

AM PM

NOTE Temperature scale default is Fahrenheit units but

may be reset to show Celsius, if desired. See page 9.

Buttons, Backlight, Timers & Settings

Buttons are located behind the small door on the right hand side of the thermostat (see figure 3).

IMPORTANT Do NOT begin pressing buttons until after you read the following section describing each button.

A pale blue display backlight illuminates for 30 seconds

each time any button is pressed.

When PROG or DAY/TIME button is pressed, a field be- gins flashing, expecting another input. Start making changes within 15 seconds or the HOME screen will re- turn.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Thermostat Buttons

Figure 3

(DOOR OPEN)

Auto

Copy

(Outside)

DAY/TIME Setting the Day and Time

Press the DAY/TIME button and set the CURRENT hour, minute, and day of week as follows:

1. AM12" will flash on the screen. Press the Up/Down ar- rows buttons to change the hour. (AM" or PM" must correspond to time of day.) Press DAY/TIME OR, if ad- justing for daylight savings time, pressing the ENTER button stores the single change and exits to the HOME screen, bypassing minutes and day of week.

2. Minutes will flash. Use the Up/Down arrow buttons to display the minutes past the hour. Press DAY/TIME.

3. Day MO" (Monday) will flash. Use Up/Down arrow buttons to display the current day. Day selections are abbreviated as MO, TU", WE", TH", FR", SA", and SU". Press DAY/TIME.

4. The HOME screen reappears; confirm day and time are correct. This completes day and time setting.

Page 39

Page 3

51M42 SERIES 5/2

HEAT Using the Heat Mode

Normal Heat Mode In normal heat mode, both the heat pump and the backup heat source are used to provide heat. If the thermostat de-

tects that the heat pump is not able to provide enough heat (as may be the case in very cold weather), then the backup heat source is activated.

Emergency Heat Mode In emergency heat mode, only the backup heat source provides heat the heat pump is disabled. The backup heat source is activated only when there is a heat demand.

Enabling Normal Heat Mode

Use the HEAT button to select normal heat mode, emer- gency heat mode, or to disable heat modes as desired. If the thermostat is in off or cool mode, pressing the HEAT

button enables heat mode. This is indicated by HEAT in the lower right corner (see figure 4).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Normal Heat Mode Enabled

Figure 4

(DOOR OPEN)

Auto

Copy

5:30

(Outside)

Enabling Emergency Heat Mode

If the thermostat is in heat mode, pressing the HEAT button

enables emergency heat mode (see figure 5). If the ther- mostat is in normal heat mode when the HEAT button is pressed, then emergency heat mode is enabled.

Emergency Heat Mode Enabled

Figure 5

ROOM

75 HEAT SETPOINT

HEAT

EMG.

Disabling Heat Mode

If the thermostat is in emergency heat mode when the HEAT button is pressed, then heat modes are disabled. This is indicated by OFF near the right side of the display as shown in figure 6.

Heat Mode Disabled

Figure 6

ROOM

75 HEAT SETPOINT

OFF

Heating Demand

The thermostat must be in either normal or emergency heat mode in order to properly control the heating equip- ment. In either heat mode, when the actual temperature is

lower than the temperature setpoint (as shown in figure 7), the thermostat detects a heating demand and activates the heating equipment to satisfy the demand. Heating opera- tion is indicated by a flame icon in bottom righthand corner of the display.

Heating Demand

Figure 7

ROOM

75 HEAT SETPOINT

HEAT

When the actual temperature rises above the temperature setpoint, the flame icon will disappear. This indicates that the heating demand has been satisfied and that the heat- ing equipment has been turned off.

NOTE The heat pump is activated for at least 4 minutes if

no buttons are pressed during the demand interval. The

backup heat source is activated for at least 3 minutes if no

buttons are pressed during the demand interval.

If your system supports 3stage heating (as does the 51M42 thermostat), you may notice various heating levels being delivered during a demand.

If a small heat pump heating demand is present, "Lo" is dis- played in the SYSTEM box; if a large heat pump heating demand is present, "Hi" is displayed (see figure 8).

Large Heat Heating Demand

Figure 8

ROOM

75 HEAT SETPOINT

HEAT

Hi Lo

Page 40

Page 4

505069M 07/05

COOL Using the Cool Mode

Enabling and Disabling Cool Mode

Use the COOL button to enable or disable cool mode as desired. If the thermostat is in heat or off mode, cool mode is enabled when the COOL button is pressed. This is indi- cated by COOL on the right side of the display (see figure 9).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Turn Cool ON/OFF

Figure 9

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

If the thermostat is in cool mode, pressing the COOL but- ton disables cool mode (indicated by OFF on the right side of the display).

Cooling Demand

Set the thermostat to cool mode to control the cooling equipment. Then, if the room temperature is higher than the temperature setpoint, as shown in figure 10, the ther- mostat detects a cooling demand and will activate the cool-

ing equipment to satisfy the demand.

Cooling Demand

Figure 10

ROOM

Hi Lo

FAN AUTO

COOL76

68 HEAT SETPOINT

COOL SETPOINT

Cooling operation is indicated by flashing snowflake" icons. When the actual temperature drops below the tem- perature setpoint, the snowflake icons will disappear. This indicates that the cooling demand has been satisfied and that the cooling equipment has been turned off.

If your system supports 2stage cooling (as does the

51M42 thermostat), you may notice various cooling levels being delivered during a demand. Also, if a small cooling demand is present, "Lo" will be displayed in the SYSTEM box. However, if a large cooling demand is present, "Hi" will be displayed in the lower right side of the display (shown in figure 10).

NOTE If no buttons are pressed during a demand for

cooling, the equipment must operate for at least 4 minutes.

After a demand has been satisfied, cooling equipment op-

eration is locked out for 5 minutes. If another cooling de-

mand occurs during this 5minute interval, COOL" and the

snowflakes will flash; however, the cooling equipment will

not operate until the 5minute delay has elapsed.

AUTO Using the Autochangeover Mode

Autochangeover can be used in either of the thermostat hold modes, or when the thermostat program is running. These modes are described later.

HOLD Using Temperature Hold Modes

When the HOLD button is displayed at the HOME screen, the thermostat is in a temperature hold condition. This

means that the temperature program data is ignored and the thermostat functions much like a nonprogrammable thermostat.

Adjusting Temperature Setpoint in Hold Mode The temperature setpoint represents the desired tempera- ture of the space around the thermostat. The default heat setpoint in hold mode is 70F; the default cool setpoint in hold mode is 78F.

To adjust the setpoint, press the UP or DOWN () arrow buttons (see figure 11); the existing setpoint is displayed to the right of the actual room temperature. Each button press adjusts the setpoint up or down by 1 degree.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Hold Temperature Mode

Figure 11

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

After the desired setpoint is reached, the HOME screen will reappear after about 15 seconds.

Permanent Hold Mode At any time the program is running, from the HOME screen, set a permanent hold (program override) by press- ing the HOLD button (see figure 11). The thermostat now functions much like a nonprogrammable thermostat. Use the Up/Down arrow buttons to adjust the hold setpoint. To return to the program, press the HOLD button again.

Page 41

Page 5

51M42 SERIES 5/2

Temporary (2-Hour) Hold

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Temporary Hold Temperature Mode

Figure 12

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

While in Temporary Hold, press the HOLD button once to switch to Permanent Hold (HOLD displays solid; PROG not displayed); press the HOLD button again to return to the program (PROG displays; HOLD not displayed).

PROG Thermostat Programming

The 51M42 thermostat can be programmed to perform a set of both heating and cooling events for each day of the week. Each day can be programmed for 4 unique events per day, and each day can be different from any other day.

To Set Program Events and Temperatures Figure 13 gives an example of how up to 7 different pro- grams can be set. Programs A and C reflect the desired warmth while the home IS occupied (72); B allows less heating while the home is NOT occupied; D reflects a cool sleeping temperature.

NOTE The example in figure 13 shows heat setpoints; a

similar program may be set for cool setpoints.

1. Press and release the PROG button. "MO" (Monday), "AM 6:00", period "A", "COOL SETPOINT 78", and "HEAT SETPOINT 70" are displayed. "AM 6" flashes.

3. Use the Up/Down arrow buttons to select the desired heat setpoint; press the PROG button.

4. Use the Up/Down arrow buttons to select the desired cool setpoint; press the PROG button.

NOTE Pressing the ENTER button during the following programming steps, saves and exits to the HOME screen.

To program events and temperatures, perform the follow- ing steps.

Figure 13

Program Example

6AM NOON 6PM MID 6AM NIGHT

B D

B C

A B C

A B

C D

SATURDAY PROGRAM: 72

SUNDAY PROGRAM: 72

FRIDAY PROGRAM: 72

THURSDAY PROGRAM: 72

WEDNESDAY PROGRAM: 72

TUESDAY PROGRAM: 72

MONDAY PROGRAM: 72

5. Repeat steps 1 4 for Monday, periods B, C, and D.

6. COPY A PROGRAM If the program entered for Monday is satisfactory for other days of the week, do the following to repeat the same program for other days:

A Press the PROG button, then press the COPY button. The display clears the screen except for Copy from MO with MO" flashing. Press the COPY button again to copy Mondays program.

B The display changes to Copy to MO". Use the ar- row buttons to scroll to the desired day where you want the same program as Monday. Press the COPY button.

C Repeat steps A and B for as many days as you want the same program.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Copy a Programmed Day to Another Day

Figure 14

(DOOR OPEN)

Auto

Copy

Copy from MO

(Outside)

7. Repeat steps 1 5 to program different times and tem- peratures for days not yet programmed.

Page 42

Page 6

505069M 07/05

FAN Controlling the Fan Operation

Use the FAN button to select either continuous fan mode or

auto fan mode.

To change from continuous to auto fan mode (or vice ver- sa), press the FAN button. Note whether a fan icon in the FAN box is present (indicating that the fan is running) or not (fan not running).

If continuous fan mode is enabled (ON displayed in FAN box see figure 15), the fan will run continuously regard-

less of whether the heating or cooling equipment is run- ning.

Using Fan ON

Figure 15

Heat

Prog

Fan

Cool

Day/Time

Hold

Auto

Copy

i0:30

If auto fan mode is selected (AUTO displayed in FAN box see figure 16), the fan will only run when the heating or cooling equipment is running.

Using Fan AUTO

Figure 16

Heat

Prog

Fan

Cool

Day/Time

Hold

Auto

Copy

i0:30

Displaying Outside Temperature

Pressing the ENTER (Outside) button at the HOME screen displays the outside temperature (see figure 17) for several seconds, then returns to room temperature.

Check Outside Temperature

Figure 17

88 Fan

Settings

Hold

Enter

(Outside)

SETTINGS Filter/Maintenance Reminders

The 51M42 thermostat is designed to remind you when the filter needs changing or when routine maintenance is re- quired, as (and if) defined, by you. These optional remind- ers are not enabled until you activate them. To do so, press the SETTINGS button (shown below the FAN button in fig- ure 16) once or twice for the desired reminder as shown in

figure 18 and as described in table 1.

Reminder Settings Display

Figure 18

FILTER

OFF

MAINTENANCE

For FILTER, press SETTINGS button 1 time

For MAINTENANCE, press SETTINGS button 2 times

The default setting for the reminders is OFF (disabled). Press Up/Down arrow buttons to select the desired re- minder intervals.

Table 1

Filter and Maintenance Reminders

Buttons to Use Reminder

Available Settings and How to Use

Settings (1st press)

FILTER Total fan run time expressed in months (Off 1 3 6 12); for

then Arrows to scroll

, , , , example, if fan runs 12 hours a day 1 month reminder displays

selections ,

in 2 calendar months.

Settings (2nd press)

then Arrows

MAINTE- NANCE

Elapsed chronological time in months (Off, 6, 12). Use this, for example to remind yourself

to scroll ,

when to perform routine checks selections or when to call a technician for

perodic preventive maintenance.

Enter Stores settings.

NOTE The HOME screen will reappear about 15 seconds

after the final arrow button press. OR, press the ENTER

button at any time to store any changes and exit to the

HOME screen.

After either programmed interval has elapsed, the remind-

er will be displayed as shown in figure 19.

Page 43

Page 7

51M42 SERIES 5/2

COOL

OFF

AUTO

EMG.

HEAT

I0:26 PROG A B C D HOLD

FAN ON AUTO FILTER SERVICE

MAINTENANCE

Reminders

Figure 19

ROOM

AM PM

COOL

OFF

AUTO

EMG.

HEAT

FAN ON AUTO FILTER SERVICE

MAINTENANCE

Service Indicator FlashingROOM

Filter & Maintenance

Indicators

After the filter has been changed or maintenance per- formed, reset the reminder by pressing the SETTINGS button for 4 seconds at the corresponding reminder set- tings screen. The screen will blink for a few moments to in- dicate that the timer has been reset.

SETTINGS Balance Point

NOTE The balance point is only available with the out-

door sensor.

When the outdoor sensor (X2658) is connected to the 51M42 thermostat, balance point adjustment is available. The balance point feature allows the measured outdoor temperature to govern operation of the heat pump and

backup heat source.

Press the SETTINGS button three times to access the Bal-

ance Point Settings screen (see figure 20).

Figure 20

Balance Point Setting

556p SETPOINT

The balance point can be set at any temperature between 1F and 55F (17C to 13C). A balance point setting of zero disables the balance point function (in this case, the thermostat behaves as if no outdoor sensor is attached). The default balance point setting is 55F.

seconds.

NOTE The balance point feature allows the outdoor tem-

perature to rise or fall 3F above or below the balance

point. This prevents excessive cycling of the equipment

when the outdoor temperature is near the balance point.

For example, if the balance point is 40F and the actual

outdoor temperature is 35F, the outdoor temperature

must rise to 43F before equipment adjustment occurs.

Conversely, if the balance point is 40F and the actual out-

door temperature is 45F, the outdoor temperature must

drop to 37F before equipment adjustment occurs.

Service Indicator

When abnormal equipment operation is detected, the SERVICE indicator will flash on the screen (see figure 19 on page 7). This indicates that the equipment requires

service from a qualified service technician.

Thermostat RESET

Under some abnormal conditions, it may be necessary to reset" the thermostat to its default condition. Such a RE- SET would delete all programming and settings and there-

fore should only be used on rare occasions when the the thermostat fails to function as designed and/or as pro- grammed. Such an instance can occur as a result of a pow- er surge or similar electrical disturbance (e.g. after an elec- trical storm or power outage). The RESET button can be used to recover from this situation.

CAUTION When the RESET button is pressed, ALL settings re- vert back to the defaults, including the default pro- gram (see tables 2 and 3).

The RESET button is an unlabeled, recessed button lo- cated behind the door, on the righthand side of the ther- mostat, below the SETTINGS button (see figure 3). Use a

paper clip or small pencil to press the RESET button; ALL thermostat settings will be reset to the defaults listed in the Default Thermostat Settings section.

Removing/Installing Thermostat

The thermostat hinges on tabs on the top of the subbase;

no tool is needed to remove the thermostat from the sub- base. Pivot the bottom of the thermostat outward (releas- ing the snaps), then lift up to remove.

To replace it, first position the top tilted toward the wall bracket and align it until you feel the tabs and slots engage; then, while the top is in place, pivot the bottom toward the wall until the thermostat snaps into place.

Page 44

Page 8

505069M 07/05

Default Thermostat Settings

Default thermostat settings are shown in table 2 and the

default program is shown in table 3.

Table 2

Default Thermostat Settings

Mode Heat (Perm. Hold)

Heat Setpoint (Perm Hold) 70F (or 21C)

Cool Setpoint (Perm Hold) 78F (or 26C)

Fan Auto

Filter Reminder OFF

Maintenance Reminder OFF

Equipment Protection Timers Reset Back to Zero

Autochangeover OFF

Table 3

Default Program Settings Time & Temp.

Programs Time Temp. Heat Temp. Cool

All days A 6:00am 70F / 21C 78F / 26C All days B 8:00am 62F / 17C 85F / 29C All days C 6:00pm 70F / 21C 78F / 26C All days D 10:00pm 62F / 17C 82F / 28C

Thermostat Output Table

Table 4 depicts the 51M42 thermostat output states for var- ious input conditions. The following notes described terms

used in the table.

NOTES:

X = output is activated with 24VAC.

BBP: outdoor temperature is below balance point

ABP: outdoor temperature is above balance point

In all cases, the state of the B terminal is opposite that of the O terminal

Data are tabulated for AUTO fan setting. If the fan set- ting is ON, the G output is activated in all cases

Upstage timers:

30 minutes (when upstaging from small to large demand)

15 minutes (HEAT MODE ONLY when upstaging from large to very large demand)

The temperature ranges expressed in the following definitions of SMALL/LARGE/VERY LARGE" de- mands are for guidance only; actual temperatures may vary:

With a SMALL heat demand, temperature is: below setpoint 0.5F but above setpoint 1.5F AND 30-minute upstage timer HAS NOT expired.

With a LARGE heat demand, temperature is: less than setpoint 1.5F OR 30-minute upstage timer HAS expired.

With a VERY LARGE heat demand, temperature is: below setpoint 2.5F OR 15minute 2nd upstage timer HAS expired.

Emergency heat demand (only if emergency heat is enabled): temperature is below setpoint 0.5F.

With a SMALL cool demand, temperature is: above setpoint +0.5F but below setpoint +1.5F AND 30-minute upstage timer HAS NOT expired.

With a LARGE cool demand, temperature is: above setpoint +1.5F OR 30-minute upstage timer HAS expired.

Table 4

THERMOSTAT OUTPUTS

Demand Condition W1 E Y1 Y2 G O

Cooling Demands

SMALL X X X

LARGE X X X X

No Demand X

Heating Demands

With Electric Backup (no outdoor sensor)

SMALL X X

LARGE X X X

VERY LARGE X X X X

Emergency X X

No Demand

With Gas Backup (dual fuel; no outdoor sensor)

SMALL X X

LARGE X X X

VERY LARGE X

Emergency X

No Demand

With Electric Backup (outdoor sensor attached)

SMALL (Above Balance Point) X X

LARGE (ABP) X X X

VERY LARGE (ABP) X X X

SMALL (Below Balance Point) X X

LARGE (BBP) X X X

VERY LARGE (BBP) X X X X

Emergency X X

No Demand

With Gas Backup (dual fuel; outdoor sensor attached)

SMALL (ABP) X X

LARGE (ABP) X X X

VERY LARGE (ABP) X

SMALL (BBP) X

LARGE (BBP) X

VERY LARGE (BBP) X

Emergency X

No Demand

Page 45

Page 9

51M42 SERIES 5/2

Technical Specifications

Thermostat Type Electronic programmable thermostat for heat pump, 3-stage heat/2-stage cool.

NOTE 2 stages of heat pump heat and one stage of auxil-

iary (gas or electric) backup heat are supported.

Power Supply Range 18VAC 30VAC (24VAC nominal), 60Hz

CAUTION 24VAC is present on the terminals of the thermostat bracket. If removing the thermostat from the wall, use caution and avoid touching any of the connec- tor terminals on the wall bracket.

Also, when working with the thermostat dip switches, use a nonconductive tool and take cau- tion to avoid making any contact with the circuit board, its imprinted circuitry and its connector prongs.

Temperature Display Display Scale: Fahrenheit or Celsius user selectable (via

DIP switch; see figure 21) Display range: 35F (2C) to 99F (37C) Display resolution: 1F (1C) Display Accuracy: +/1F

If the Fahrenheit/Celsius display must be changed, use a plastic, nonconductive tool to push the dip switch to the right position (see figure 21).

F/C (Fahrenheit/Celsius) switch shown in Celsius position

Figure 21

Changing Fahrenheit/Celsius Setting

PLUG IN (Use Care To Avoid Bending Prongs.)

Indoor Temperature Measurement Range

Measurement Scale: Fahrenheit

Measurement Range: 35F to 99F

Measurement Resolution: 0.5F

Measurement Accuracy: +/1F

Field Offset: via DIP switches to +/3F

Sampling Method: temperature measurements sampled

every 15 seconds. Displayed temperature is the average

of the last four measurements.

Outdoor Temperature Measurement Range

Measurement Scale: Fahrenheit

Measurement Range: 22F to 122F

Measurement Resolution: 1F

Measurement Accuracy: +/2F

Temperature Setpoint Range

Setting range: 50F (10C) to 90F (32C)

Setting resolution: 1F (1C)

Smart Setback Recovery (via DIP switch #6)

Smart Setback Recovery (SSR) affects the way the ther-

mostat responds to program events. If SSR is disabled, the

thermostat will react to a program event at the time the

event occurs. However, if SSR is enabled, the thermostat

will react to a program event before the event occurs such

that the desired temperature is reached at the time of the

event, not after.

Autochangeover Deadband Selection (via DIP switch #7)

Autochangeover deadband can be set to 4 or 6 degrees.

When autochangeover is enabled (via the AUTO button),

the thermostat will automatically change over from heating

to cooling and vice versa, to keep the room temperature in

between the heating and cooling setpoints. The deadband

is the minimum difference between the heating and cooling

setpoints.

Fan Control

AUTO or ON modes.

I/O Relays

All thermostat relays are latching type to minimize power

consumption.

Page 46

Page 10

505069M 07/05

Table 5

51M42 Terminal Designations

Term. Description

B Reversing valve, heat active

O Reversing valve, cool active

R 24VAC

Y1 First-stage cooling/heating, compressor energized

W1* Auxiliary heating, furnace energized

Y2 Second-stage cooling/heating, compressor energized

E* Emergency heat

G Fan control

L Service Indicator

C 24VAC common

T Outdoor temperature sensor connection 1

T Outdoor temperature sensor connection 2

* For most applications, E will be jumpered to W1. If sep-

arate wires are not provided for both E and W1, jumper

the E terminal to the W1 terminal on the thermostat sub-

base. For applications involving the use of a balance

point (whereby the outdoor temperature is to be used to

restrict either heat pump operation or backup heat

source operation), the outdoor sensor (part number

X2658) MUST be installed.

Equipment Protection Timers

Minimum Compressor OFF time: 5 minutes Minimum Compressor ON time: 4 minutes Minimum Furnace ON time: 3 minutes

Minimum furnace cycle time (elapsed time between any furnace activation and the next furnace activation): 6 min- utes.

Minimum elapsed time between any compressor activa- tion and the next compressor activation: 6 minutes.

NOTE All protection timers (except the compressor OFF

timer) can be overridden if a heating or cooling demand is

initiated or terminated using the UP, DOWN, HEAT, or

COOL buttons.

Equipment Protection Override

Both the minimum compressor OFF timer and the mini- mum equipment cycle timer can be overridden by press- ing and holding either the HEAT or COOL button down for 4 seconds.

OverTemperature Protection Thermal-mechanical switch opens W1, Y1, Y2, and E at 93F+/6F.

Filter Reminder Settings of Off, 1, 3, 6 or 12 (months of fan run time) are available. When programmed time has elapsed, a FILTER indicator is displayed.

Maintenance Reminder Settings of Off, 6 or 12 (months of chronological time) are available. When programmed time has elapsed, a mainte-

nance indicator MAINTENANCE" is displayed.

Service Reminder

The SERVICE indicator is displayed only under the follow- ing conditions:

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the R terminal;

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the C terminal.

Power Loss/Recovery Thermostat memory is retained for a minimum of 24 hours during a power loss (includes retention of clock setting, program information, HOLD status, programmed temper- ature setpoint, heat/cool and fan mode settings, filter re-

minder status, maintenance reminder status, and equip- ment protection timers). After 24 hours of power loss, programmed settings will be lost and replaced with default settings.

IMPORTANT Power must be applied for at least six consecutive hours prior to a power loss in order for memory to be retained for the specified time.

LCD Backlight Activated for 30 seconds when any button is pressed.

NOTE During an electrical storm or similar disturbance,

the backlight may activate for a few seconds. This is nor-

mal and will no longer occur after the electrical disturbance

has passed.

Thermostat Operating Conditions 35F to 105F, 5% to 90% RH

Thermostat Storage Conditions 40F to 185F, 5% to 95% RH

Page 47

07/05 505,067M

Page 1

2005 Lennox Industries Inc. Dallas, Texas, USA

RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE

51M38 Merit Series Thermostat

The Lennox Merit Series 7 day programmable electronic thermostat 51M38 provides excellent temperature control and a large, easy-to-read display. This product includes a programmable filter change reminder, an equipment maintenance reminder, and a system check indicator to notify the user when the equipment requires service.

Thermostat 51M38 is suitable for nonheat pump, single- stage heat/single-stage cool applications with either gas or electric furnace. Also, the thermostat provides auto- changeover capability.

OPERATION MANUAL

51M38 Merit Series 7 Day Programmable Thermostat

CONTROLS 505,067M 07/05

Table of Contents

51M38 Series Thermostat 1. . . . . . . . . . . . . . . . . . . . . . General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . . Buttons, Backlight, Timers & Settings 2. . . . . . . . . . . . DAY/TIME Set Day and Time 2. . . . . . . . . . . . . . . . . . HEAT Heat Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . COOL Cool Mode 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . AUTO Using the Autochangeover Mode 3. . . . . . . . . HOLD Temperature Hold Mode 4. . . . . . . . . . . . . . . . PROG Thermostat Programming 4. . . . . . . . . . . . . . . COPY Copy a Program 5. . . . . . . . . . . . . . . . . . . . . . . FAN Controlling Fan Operation 5. . . . . . . . . . . . . . . . . Displaying Outside Temperature 5. . . . . . . . . . . . . . . . . SETTINGS Filter /Maintenance Reminder 5. . . . . . . Service Indicator 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thermostat RESET 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing/Installing Thermostat 6. . . . . . . . . . . . . . . . . Default Thermostat Settings 6. . . . . . . . . . . . . . . . . . . . Thermostat Output Table 7. . . . . . . . . . . . . . . . . . . . . . . Technical Specifications 7. . . . . . . . . . . . . . . . . . . . . . . .

General

These instructions are intended as a general guide and do not supersede local codes in any way. Consult authorities having jurisdiction before installation.

Check equipment for shipping damage. If you find any damage, immediately contact the last carrier.

Introduction

This document describes the operation of Lennox thermo- stat 51M38. Refer to the installation manual for instructions regarding installation and wiring of the thermostat.

Initial Thermostat Power-up

When power is initially applied to the thermostat, the dis-

play will appear as shown in figure 1.

HEAT SETPOINT

COOL

OFF

AUTO

EMG.

HEAT

I8:88

i88 Figure 1

AM PM

OUTROOM

MO TU WE TH FR SA SU

COOL SETPOINT

Initial PowerUp Display

FILTER

MAINTENANCE

Hi Lo

FAN ON AUTO

SERVICE

Copy tofrom

PROG A B C D

HOLD

All display segments are momentarily activated. This oc-

curs as a normal part of thermostat initialization.

Litho U.S.A.

Page 48

Page 2

505067M 7/13/05

Within a few seconds, the HOME screen appears (see fig-

ure 2) with default settings as shown. After about 1 minute

of initialization time, the actual room temperature will be

displayed.

COOL

OFF

AUTO

EMG.

HEAT

I0:26 PROG A B C D HOLD

FAN ON AUTO

HOME Screen

Figure 2

ROOM

AM PM

NOTE Temperature scale default is Fahrenheit units but

may be reset to show Celsius, if desired. See page 7.

Buttons, Backlight, Timers & Settings

Buttons are located behind the small door on the right hand side of the thermostat (see figure 3).

IMPORTANT Do NOT begin pressing buttons until after you read the following section describing each button.

A pale blue display backlight illuminates for 30 seconds each time any button is pressed.

When the PROG or DAY/TIME button is pressed, a field begins flashing, expecting another input. Start making changes within 15 seconds or the HOME screen will re- turn.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Thermostat Buttons

Figure 3

(DOOR OPEN)

Auto

Copy

(Outside)

DAY/TIME Setting the Day and Time

Press the DAY/TIME button and set the CURRENT hour, minute, and day of week as follows:

1. AM12" will flash on the screen. Press the UP/DOWN arrows to change the hour. (AM" or PM" must corre- spond to time of day.) Press the DAY/TIME button OR, if adjusting for daylight savings time, pressing the EN- TER button stores the single change and exits to the HOME screen, bypassing minutes and day of week.

2. Minutes will flash. Use the UP/DOWN arrow button to display the minutes past the hour. Press the DAY/ TIME button.

3. Day MO" (Monday) will flash. Use UP or DOWN arrow buttons to display the current day. Day selections are abbreviated as MO, TU", WE", TH", FR", SA", and SU". Press the DAY/TIME button.

4. The HOME screen reappears; confirm day and time are correct. This completes day and time setting.

Page 49

Page 3

51M38 SERIES 5/2

HEAT Using the Heat Mode

Enabling and Disabling Heat Mode

The thermostat must be in the heat mode to control the heating equipment. Press the HEAT button to enable or disable heat mode. If the thermostat is in cool or off mode, pressing the HEAT button enables the heat mode (indi- cated by HEAT in the lower right corner see figure 4).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Turn Heat ON/OFF

Figure 4

(DOOR OPEN)

Auto

Copy

(Outside)

5:30

If the thermostat is in heat mode, heat mode is disabled when the HEAT button is pressed. This is indicated by OFF near the right side of the display as shown in figure 5.

Heat/Cool Mode Disabled

Figure 5

ROOM

75 HEAT SETPOINT

OFF

Heating Demand

Figure 6

ROOM

75 HEAT SETPOINT

HEAT

Heating operation is indicated by a flame icon in the lower right corner. When the actual temperature rises above the temperature setpoint, the flame icon will disappear. This indicates that the heating demand has been satisfied and that the heating equipment has been turned off.

NOTE Heating equipment is activated for at least 3 min- utes if no buttons are pressed during the demand interval.

COOL Using the Cool Mode

Enabling and Disabling Cool Mode Use the COOL button to enable or disable cool mode as desired. If the thermostat is in heat or off mode, cool mode is enabled when the COOL button is pressed. This is indi- cated by COOL on the right side of the display (see figure

7).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Turn Cool ON/OFF

Figure 7

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

If the thermostat is in cool mode, pressing the COOL but- ton disables cool mode (indicated by OFF, similar to figure 5).

Cooling Demand Set the thermostat to cool mode to control the cooling equipment. Then, if the room temperature is higher than

the temperature setpoint, as shown in figure 7, the thermo- stat detects a cooling demand and will activate the cooling equipment to satisfy the demand.

Cooling operation is indicated by flashing snowflake" icons in the display. When the actual temperature drops below the temperature setpoint, the snowflake icons will disappear. This indicates that the cooling demand has been satisfied and that the cooling equipment has been turned off.

NOTE The cooling setpoint cannot be lower than the heating setpoint. Also, the difference between the cooling and heating setpoint must be at least 4 degrees.

AUTO Using the Autochangeover Mode

When in either heat mode or cool mode, autochangeover can be enabled or disabled by pressing the AUTO button. If

enabled, AUTO appears at the lower right corner of the dis- play. The thermostat will then automatically change over from heating to cooling and vice versa, to keep the room temperature in between the heating and cooling setpoints. Autochangeover can be used in either of the thermostat hold modes, or when the thermostat program is running.

These modes are described later.

Page 50

Page 4

505067M 7/13/05

HOLD Using Temperature Hold Modes

Adjusting Temperature Setpoint in Hold Mode

The temperature setpoint represents the desired tempera- ture of the space around the thermostat. The default heat setpoint in hold mode is 70F; the default cool setpoint in hold mode is 78F.

To adjust the setpoint, press the UP or DOWN () arrow buttons (see figure 8); the existing setpoint is displayed to

the right of the actual room temperature. Each button press adjusts the setpoint up or down by 1 degree.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Hold Temperature Mode

Figure 8

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

After the desired setpoint is reached, the HOME screen will reappear after about 15 seconds.

Permanent Hold Mode

At any time the program is running, from the HOME screen, set a permanent hold (program override) by press- ing the HOLD button (see figure 8). The thermostat now functions much like a nonprogrammable thermostat. Use the Up/Down arrow buttons to adjust the hold setpoint. To return to the program, press HOLD again.

Temporary (2-Hour) Hold

While in Temporary Hold, press HOLD once to switch to Permanent Hold (HOLD displays solid; PROG not dis-

played); press HOLD again to return to the program (PROG displays; HOLD not displayed).

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Temporary Hold Temperature Mode

Figure 9

(DOOR OPEN)

Auto

Copy

(Outside)

i0:30

PROG Thermostat Programming

The 51M38 thermostat can be programmed to perform a set of both heating and cooling events for each day of the week. Each day can be programmed for 4 unique events per day, and each day can be different from any other day.

To Set Program Events and Temperatures Figure 10 gives an example of how up to 7 different pro- grams can be set. Programs A and C reflect the desired warmth while the home IS occupied (72); B allows less heating while the home is NOT occupied; D reflects a cool sleeping temperature.

NOTE The example in figure 10 shows heat setpoints; a

similar program may be set for cool setpoints.

Figure 10

Program Example

6AM NOON 6PM MID 6AM NIGHT

B D

B C

A B C

A B

C D

SATURDAY PROGRAM: 72

SUNDAY PROGRAM: 72

FRIDAY PROGRAM: 72

THURSDAY PROGRAM: 72

WEDNESDAY PROGRAM: 72

TUESDAY PROGRAM: 72

MONDAY PROGRAM: 72

NOTE Pressing the ENTER button during the following programming steps, saves and exits to the HOME screen.

To program events and temperatures, perform the follow- ing steps.

Page 51

Page 5

51M38 SERIES 5/2

1. Press and release the PROG button. "MO" (Monday), "AM 6:00", period "A", "COOL SETPOINT 78", and "HEAT SETPOINT 70" are displayed. "AM 6" flashes.

3. Use the Up/Down arrow buttons to select the desired heat setpoint; press the PROG button.

4. Use the Up/Down arrow buttons to select the desired cool setpoint; press the PROG button.

5. Repeat steps 1 4 for Monday, periods B, C, and D.

6. COPY A PROGRAM If the program entered for Monday is satisfactory for other days of the week, do the following to repeat the same program for other days:

A Press the PROG button, then press the COPY button. The display clears the screen except for Copy from MO with MO" flashing. Press the COPY button again to copy Mondays program.

B The display changes to Copy to MO". Use the ar- row buttons to scroll to the desired day where you want the same program as Monday. Press the COPY button.

C Repeat steps A and B for as many days as you want the same program.

Heat

Prog

Fan

Settings

Cool

Day/Time

Hold

Enter

Copy a Programmed Day to Another Day

Figure 11

(DOOR OPEN)

Auto

Copy

(Outside)

Copy from MO

7. Repeat steps 1 5 to program different times and tem- peratures for days not yet programmed.

FAN Controlling the Fan Operation

Use the FAN button to select either continuous fan mode or auto fan mode.

To change from continuous to auto fan mode (or vice ver- sa), press the FAN button. Note whether a fan icon in the FAN box is present (indicating that the fan is running) or not (fan not running).

If continuous fan mode is enabled (ON displayed in FAN box see figure 12), the fan will run continuously regard- less of whether the heating or cooling equipment is run- ning.

Using Fan ON

Figure 12

Heat

Prog

Fan

Cool

Day/Time

Hold

Auto

Copy

i0:30

If auto fan mode is selected (AUTO displayed in FAN box see figure 13), the fan will only run when the heating or cooling equipment is running.

Using Fan Auto

Figure 13

Heat

Prog

Fan

Cool

Day/Time

Hold

Auto

Copy

i0:30

Displaying Outside Temperature

Pressing the ENTER (Outside) button at the HOME screen displays the outside temperature (see figure 14) for several seconds, then returns to room temperature.

Check Outside Temperature

Figure 14

88 Fan

Settings

Hold

Enter

(Outside)

SETTINGS Filter/Maintenance Reminders

The 51M38 thermostat is designed to remind you when the filter needs changing or when routine maintenance is re- quired, as (and if) defined, by you. These optional remind- ers are not enabled until you activate them. To do so, press the SETTINGS button once or twice for the desired re- minder as shown in figure 15 and as described in table 1.

Reminder Settings Display

Figure 15

FILTER

OFF

MAINTENANCE

For FILTER, press SETTINGS button 1 time

For MAINTENANCE, press SETTINGS button 2 times

Page 52

Page 6

505067M 7/13/05

The default setting for the reminders is OFF (disabled). Press Up/Down arrow buttons to select the desired re- minder intervals.

Table 1

Filter and Maintenance Reminders

Buttons to Use Reminder

Available Settings and How to Use

SETTINGS (1st press)

FILTER Total fan run time expressed in months (Off 1 3 6 12); for

then Arrows to scroll

, , , , example, if fan runs 12 hours a day 1 month reminder displays

selections ,

in 2 calendar months.

SETTINGS (2nd press)

then Arrows

MAINTE- NANCE

Elapsed chronological time in months (Off, 6, 12). Use this, for example to remind yourself

to scroll ,

when to perform routine checks selections or when to call a technician for

perodic preventive maintenance.

Enter Stores settings.

NOTE The HOME screen will reappear about 15 seconds after the final arrow button press. OR, press the ENTER button at any time to store any changes and exit to the HOME screen.

After either programmed interval has elapsed, the remind- er will be displayed as shown in figure 16.

COOL

OFF

AUTO

EMG.

HEAT

I0:26 PROG A B C D HOLD

FAN ON AUTO FILTER SERVICE

MAINTENANCE

Reminders

Figure 16

ROOM

AM PM

COOL

OFF

AUTO

EMG.

HEAT

FAN ON AUTO FILTER SERVICE

MAINTENANCE

Service Indicator FlashingROOM

Filter & Maintenance

Indicators

Service Indicator

When abnormal equipment operation is detected, the SERVICE indicator will flash on the screen (see figure 16). This indicates that the equipment requires service from a qualified service technician.

Thermostat RESET

Under some abnormal conditions, it may be necessary to reset" the thermostat to its default condition. Such a RE- SET would delete all programming and settings and there- fore should only be used on rare occasions when the the thermostat fails to function as designed and/or as pro- grammed. Such an instance can occur as a result of a pow- er surge or similar electrical disturbance (e.g. after an elec- trical storm or power outage). The RESET button can be used to recover from this situation.

CAUTION When the RESET button is pressed, ALL settings re- vert back to the defaults, including the default pro- gram (see tables 2 and 3).

Removing/Installing Thermostat

To replace it, first position the top tilted toward the wall bracket and align it until you feel the tabs and slots engage;

then, while the top is in place, pivot the bottom toward the wall until the thermostat snaps into place.

Default Thermostat Settings

Default thermostat settings are in table 2 and the default program is shown in table 3.

Table 2

Default Thermostat Settings

Mode Heat (Perm. Hold)

Heat Setpoint (Perm Hold) 70F (or 21C)

Cool Setpoint (Perm Hold) 78F (or 26C)

Fan Auto

Filter Reminder OFF

Maintenance Reminder OFF

Equipment Protection Timers Reset Back to Zero

Autochangeover OFF

Page 53

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51M38 SERIES 5/2

Table 3

Default Program Settings (Time & Temp.)

Programs Time Temp. Heat Temp. Cool

All days A 6:00am 70F / 21C 78F / 26C All days B 8:00am 62F / 17C 85F / 29C All days C 6:00pm 70F / 21C 78F / 26C All days D 10:00pm 62F / 17C 82F / 28C

Thermostat Output Table

Table 4 depicts the 51M38 thermostat output states for var- ious input conditions.

Table 4

Thermostat Outputs

Condition W1 Y1 G

Gas Heat, Auto Fan

Heat Demand X

Cool Demand X X

No Demand

Gas Heat, Continuous Fan

Heat Demand X X

Cool Demand X X

No Demand X

Electric Heat, Auto Fan

Heat Demand X X

Cool Demand X X

No Demand

Electric Heat, Continuous Fan

Heat Demand X X

Cool Demand X X

No Demand X

NOTE X = output is activated with 24VAC.

Technical Specifications

Thermostat Type

Electronic programmable thermostat for 1-Stage Heat/1-Stage Cool, gas or electric heat, nonheat pump, nonpower robbing applications.

Power Supply Range

18VAC 30VAC (24VAC nominal), 60Hz

CAUTION 24VAC is present on the terminals of the thermostat bracket. If removing the thermostat from the wall, use caution and avoid touching any of the connec- tor terminals on the wall bracket.

Also, when working with the thermostat dip switches, use a nonconductive tool and take cau- tion to avoid making any contact with the circuit board, its imprinted circuitry and its connector prongs.

Temperature Display Display Scale: Fahrenheit or Celsius user selectable (via DIP switch; see figure 17) Display range: 35F (2C) to 99F (37C) Display resolution: 1F (1C)

Display Accuracy: +/1F

If the Fahrenheit/Celsius display must be changed, use a

plastic, nonconductive tool to push the dip switch to the right position (see figure 17).

F/C (Fahrenheit/Celsius) switch shown in Celsius position

Figure 17

Changing Fahrenheit/Celsius Setting

PLUG IN (Use Care To Avoid Bending Prongs.)

Indoor Temperature Measurement Range Measurement Scale: Fahrenheit Measurement Range: 35F to 99F Measurement Resolution: 0.5F Measurement Accuracy: +/1F Field Offset: via DIP switches to +/3F

Sampling Method: temperature measurements sampled every 15 seconds. Displayed temperature is the average of the last four measurements.

Outdoor Temperature Measurement Range Measurement Scale: Fahrenheit

Measurement Range: 22F to 122F Measurement Resolution: 1F Measurement Accuracy: +/2F

Temperature Setpoint Range Setting range: 50F (10C) to 90F (32C)

Setting resolution: 1F (1C)

Page 54

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505067M 7/13/05

Smart Setback Recovery (via DIP switch #6)

Smart Setback Recovery (SSR) affects the way the ther- mostat responds to program events. If SSR is disabled, the thermostat will react to a program event at the time the event occurs. However, if SSR is enabled, the thermostat will react to a program event before the event occurs such that the desired temperature is reached at the time of the event, not after.

Autochangeover Deadband Selection (via DIP switch #7)

Autochangeover deadband can be set to 4 or 6 degrees. When autochangeover is enabled (via the AUTO button), the thermostat will automatically change over from heating to cooling and vice versa, to keep the room temperature in between the heating and cooling setpoints. The deadband

is the minimum difference between the heating and cooling setpoints.

Fan Control

AUTO or ON modes, gas or electric heat compatible via DIP switches (also see Thermostat Output section).

I/O Relays

All thermostat relays are latching type to minimize power consumption.

Table 5

51M38 Terminal Designations

Terminal Description

R 24VAC

Y1 First stage cooling

W1 First stage heating

G Fan control

L Service Indicator

C 24VAC common

T Outdoor temperature sensor connection 1

T Outdoor temperature sensor connection 2

Equipment Protection Timers

Minimum Compressor OFF time: 5 minutes Minimum Compressor ON time: 4 minutes Minimum Furnace ON time: 3 minutes

Minimum furnace cycle time (elapsed time between any furnace activation and the next furnace activation): 6 min- utes.

Minimum elapsed time between any compressor activa- tion and the next compressor activation: 6 minutes.

NOTE All protection timers (except the compressor OFF timer) can be overridden if a heating or cooling demand is initiated or terminated using the UP, DOWN, HEAT, or COOL buttons.

OverTemperature Protection Thermal-mechanical switch opens W1 at 93F+/6F.

Filter Reminder Settings of Off, 1, 3, 6 or 12 (months of fan run time) are available. When programmed time has elapsed, a FILTER indicator is displayed.

Maintenance Reminder Settings of Off, 6 or 12 (months of chronological time) are available. When programmed time has elapsed, a MAIN- TENANCE indicator is displayed.

Service Reminder The SERVICE indicator is displayed only under the follow- ing conditions:

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the R terminal;

if the thermostat Y1 terminal has been activated with 24VAC for at least 5 minutes, AND the L terminal is shorted to the C terminal.

Power Loss/Recovery Thermostat memory is retained for a minimum of 24 hours

during a power loss (includes retention of clock setting, program information, HOLD status, programmed temper- ature setpoint, heat/cool and fan mode settings, filter re- minder status, maintenance reminder status, and equip- ment protection timers). After 24 hours of power loss, programmed settings will be lost and replaced with default settings.

IMPORTANT Power must be applied for at least six consecutive hours prior to a power loss in order for memory to be retained for the specified time.

LCD Backlight Activated for 30 seconds when any button is pressed.

NOTE During an electrical storm or similar disturbance,

the backlight may activate for a few seconds. This is nor-

mal and will no longer occur after the electrical disturbance

has passed.

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