Lennox Merit 51M37 Operation Manual
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Lennox Merit 51M37 Operation Manual

Merit series 5/2 day programmable thermostat
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E2005 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
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
dual−fuel compatibility.
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.
05/05
*2P0505*
51M37
provides
excellent
OPERATION
MANUAL
51M37 Merit
5/2 Day Programmable Thermostat
CONTROLS
505,050M
05/05
Supersedes 03/05
Table of Contents
51M37 Series Thermostat
General
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Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Initial Thermostat Power-up
Buttons, Backlight, Timers & Settings
DAY/TIME − Set Day and Time
HEAT − Heat Mode
COOL − Cool Mode
HOLD − Temperature Hold Mode
PROG − Thermostat Programming
FAN − Controlling Fan Operation
SETTINGS − Filter and Maintenance Reminders
SETTINGS − Balance Point
Service Indicator
Thermostat RESET
Removing/Installing Thermostat
Default Thermostat Settings
Technical Specifications
Thermostat Output Table
Initial Power−Up Display
MO TU WE TH FR SA SU
I8:88
AM
PM
PROG
A | B | C | D
ROOM
88
All display segments are momentarily activated. This oc-
curs as a normal part of thermostat initialization.
Page 1
®
Series
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MAINT
FILTER
SERVICE
FAN
HOLD
ON
AUTO
SYSTEM
SETPOINT
COOL
°
88
°
OFF
EMG.
HEAT
Figure 1
505,050M
*P505050M*
Litho U.S.A.
1
1
1
1
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6
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7
7
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10
Hi
Lo

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Summary of Contents for Lennox Merit 51M37

  • Page 1 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 dual−fuel compatibility.
  • Page 2 ROOM ° Figure 2 At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70°F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.
  • Page 3 3 minutes if no buttons are pressed during the demand interval. If your system supports 3−stage heating (as does the 51M37 thermostat), you may notice various heating levels being delivered during a demand. SYSTEM If a small heat pump heating demand is present, "Lo"...

  • Page 4: Enabling And Disabling Cool Mode

    If your system supports 2−stage 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.

  • Page 5: Using Temperature Hold Modes

    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.

  • Page 6: Controlling Fan Operation

    ° Figure 17 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...
  • Page 7 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;...
  • Page 8 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 70°F (or 21°C) Auto Filter Reminder Maintenance Reminder Equipment Protection...
  • Page 9 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.
  • Page 10 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: S X = output is activated with 24VAC. S BBP: outdoor temperature is below balance point...

  • Page 11: Table Of Contents

    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. 05/05 *2P0505*...

  • Page 12: Buttons, Backlight, Timers & Settings

    ROOM ° Figure 2 At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70°F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.
  • Page 13 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 −...

  • Page 14: Prog − Thermostat Programming

    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 70°F. To adjust the setpoint, press the UP or DOWN (YB) arrow buttons (see figure 9);...

  • Page 15: Fan − Controlling Fan Operation

    ° Figure 14 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...

  • Page 16: Service Indicator

    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. 505049M 5/1/05 Removing and Installing Thermostat The thermostat hinges on tabs on the top of the subbase;...
  • Page 17 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.
  • Page 18 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,...

  • Page 19: General

    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. 05/05 *2P0505*...

  • Page 20: Buttons, Backlight, Timers & Settings

    ROOM ° Figure 2 At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70°F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.
  • Page 21 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 −...

  • Page 22: Hold − Temperature Hold Mode

    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 70°F. To adjust the setpoint, press the UP or DOWN (YB) arrow buttons (see figure 9);...

  • Page 23: Fan − Controlling Fan Operation

    ° Figure 14 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...

  • Page 24: Removing/Installing Thermostat

    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. 505048M 5/1/05 Removing/Installing Thermostat The thermostat hinges on tabs on the top of the subbase;...

  • Page 25: Technical Specifications

    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.

  • Page 26: Thermostat Output Table

    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,...

  • Page 27: Initial Power−Up Display

    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. 07/05 *2P0705*...

  • Page 28: Buttons, Backlight, Timers & Settings

    ROOM ° Figure 2 At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70°F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.
  • Page 29 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...

  • Page 30: Auto − Using The Autochangeover Mode

    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 70°F; the default cool setpoint in hold mode is 78°F.
  • Page 31 Program Example MONDAY PROGRAM: 72° 68° 64° TUESDAY PROGRAM: 72° 68° 64° WEDNESDAY PROGRAM: 72° 68° 64° THURSDAY PROGRAM: 72° 68° 64° FRIDAY PROGRAM: 72° 68° 64° SATURDAY PROGRAM: 72° 68° 64° SUNDAY PROGRAM: 72° 68° 64° NOON Figure 11 NOTE −...

  • Page 32: Displaying Outside Temperature

    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 6...

  • Page 33: Default Thermostat Settings

    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.

  • Page 34: Technical Specifications

    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.
  • Page 35 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-...

  • Page 37: Play Will Appear As Shown In Figure

    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. 07/05 *2P0705*...

  • Page 38: Buttons, Backlight, Timers & Settings

    ROOM ° Figure 2 At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70°F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.

  • Page 39: Heat − 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.

  • Page 40: Auto − Using The Autochangeover 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...

  • Page 41: Prog − Thermostat Programming

    (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.

  • Page 42: Fan − Controlling Fan Operation

    Figure 17 505069M 07/05 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...

  • Page 43: Settings − Balance Point

    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;...

  • Page 44: Default Thermostat Settings

    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) 70°F (or 21°C) Cool Setpoint (Perm Hold) 78°F (or 26°C)

  • Page 45: Technical Specifications

    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.
  • Page 46 * 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...

  • Page 47: Day/Time − Set Day And Time

    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. 07/05 *2P0705*...

  • Page 48: Buttons, Backlight, Timers & Settings

    ROOM ° Figure 2 At this point, the thermostat will be fully functional; its de- fault temperature setpoint (not shown) is 70°F. At this point, if the equipment has been fully powered and if a heat demand were present, the system would begin operating.

  • Page 49: Auto − Using The Autochangeover 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 −...

  • Page 50: Prog − Thermostat Programming

    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 70°F; the default cool setpoint in hold mode is 78°F.

  • Page 51: Fan − Controlling Fan Operation

    Enter SETTINGS − Filter/Maintenance Reminders (Outside) 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.

  • Page 52: Service Indicator

    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/Installing Thermostat The thermostat hinges on tabs on the top of the subbase;...

  • Page 53: Thermostat Output Table

    All days − C 6:00pm 70_F / 21°C All days − D 10:00pm 62_F / 17°C Thermostat Output Table Table 4 depicts the 51M38 thermostat output states for var- ious input conditions. Table 4 Thermostat Outputs Condition Gas Heat, Auto Fan...
  • Page 54 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.

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