Lennox 51M32 User Manual

®

OPERATION

2003 Lennox Industries Inc.

Dallas, Texas, USA

MeritR Series Thermostat

The Lennox Merit® Series Thermostat 51M32 is a nonpro­grammable electronic thermostat that is easy-to-use and
has a large, easy-to-read display and excellent tempera­ture control. The thermostat also includes a programmable
filter change reminder and a system check indicator. The
system check indicator will notify the user of the need for
equipment service.

Thermostat 51M32 is suitable for non-heat pump, single−
stage heat/single cool applications that are matched with a
gas or electric furnace.

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
51M32. 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 dis­play will appear as shown in figure 1.

MANUAL

Merit® Series Thermostat

CONTROLS (51M32)

504,865M
09/04

RETAIN THESE INSTRUCTIONS

FOR FUTURE REFERENCE

Table of Contents

Merit® Series Thermostat 1. . . . . . . . . . . . . . . . . . . . . .

General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Initial Thermostat Power-up 1. . . . . . . . . . . . . . . . . . . . . .

Heating Control 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cooling Control 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Adjusting Temperature Setpoint 3. . . . . . . . . . . . . . . . . .

Fan Control 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Filter Reminder 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Service Indicator 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Thermostat Reset 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Default Thermostat Settings 5. . . . . . . . . . . . . . . . . . . . .

Technical Specifications 5. . . . . . . . . . . . . . . . . . . . . . . . .

Thermostat Output Table 6. . . . . . . . . . . . . . . . . . . . . . . .

Display − Initial Power−Up

ROOM

Litho U.S.A.

FILTER

SERVICE

88

FAN
ON

AUTO

SETPOINT

All display segments are momentarily activated. This oc­curs as a normal part of thermostat initialization. Within a
few seconds, the display will appear as shown in figure 2
(figure shows temperature in Fahrenheit units).

88

Figure 1

SYSTEM
COOL
OFF

EMG.
HEAT

Page 1

Display − Home Screen

Heat Mode Enabled

ROOM

70

FAN

AUTO

SYSTEM

HEAT

Figure 2

Figure 2 illustrates the HOME screen. Note that an indoor
room temperature of 70°F is initially displayed. After about
1 minute of warm−up time, the actual room temperature will
be displayed. HEAT mode is the system default (as indi­cated in the SYSTEM box at lower right).

A pale blue display backlight will turn on each time a key is
pressed. The backlight will turn off 8 seconds after the last
key is pressed.

Heating Control

The HEAT button is located behind the small door on the
right−hand side of the thermostat. See figure 3.

ROOM

69

FAN

AUTO

SETPOINT

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.

ROOM

64

Figure 4

Heat Mode Disabled

SYSTEM

HEAT

69

FAN

Additional Thermostat Buttons

Figure 3

Enabling and Disabling Heat Mode

Use the HEAT button to enable or disable heat mode as de­sired. If the thermostat is in off mode, heat mode is enabled
when the HEAT button is pressed. This is indicated by
HEAT in the SYSTEM box as shown in figure 4.

AUTO

SETPOINT

Heating Demand

The thermostat must be in heat mode in order to properly
control the heating equipment. When in heat mode, if the
actual temperature is lower than the temperature setpoint, a
heating demand is detected by the thermostat. The thermo­stat will then activate the heating equipment to satisfy the de­mand. Heating operation is indicated by a flame icon in the
SYSTEM box as shown in figure 6.

64

Figure 5

SYSTEM

OFF

Page 2

Heating Demand

Cooling Demand

ROOM

72

FAN

AUTO

88

Figure 6

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 − The heating equipment is activated for at least 3
minutes if no buttons are pressed during the demand inter­val.

Cooling Control

The COOL button is located behind the small door on the
right-hand side of the thermostat. See figure 3.

Enabling and Disabling Cool Mode

Use the COOL button to enable or disable cool mode as
necessary. If the thermostat is in off mode, cool mode is en­abled when the COOL button is pressed. This is indicated
by COOL in the SYSTEM box.

If the thermostat is in cool mode, cool mode is disabled
when the COOL button is pressed. This is indicated by OFF
in the SYSTEM box.

Cooling Demand

The thermostat must be in cool mode in order to properly
control the cooling equipment. When in cool mode, if the
room temperature is higher than the temperature setpoint,
a cooling demand is detected by the thermostat.

The thermostat will then activate the cooling equipment to
satisfy the demand. Cooling operation is indicated by a
snowflake icon in the SYSTEM box as shown in figure 7.
When the actual temperature drops below the temperature
setpoint, the snowflake icon will disappear. This indicates
that the cooling demand has been satisfied and that the
cooling equipment has been turned off.

SYSTEM

HEAT

ROOM

79

FAN

AUTO

SYSTEM
COOL

Figure 7

NOTE − The cooling equipment is activated for at least 4
minutes if no buttons are pressed during the demand inter­val. Cooling equipment operation is locked out for 5 min­utes after a demand has been satisfied. If another cooling
demand occurs during this 5−minute interval, the snowflake
icon will flash; however, the cooling equipment will not run
until the 5−minute delay has elapsed.

Adjusting Temperature Setpoint

The temperature setpoint represents the desired tempera­ture of the space around the thermostat. The default tem­perature setpoint is 70°F. To adjust the setpoint, press the
UP or DOWN arrow keys to the right of the display screen.

The existing setpoint will be displayed just below the actual
room temperature as shown in figure 8. Use the UP or
DOWN arrow keys to adjust the setpoint up or down. The
setpoint will increase by 1°F each time the UP key is
pressed. The setpoint will decrease by 1°F each time the
DOWN key is pressed.

Setpoint Display and Adjustment

ROOM

69

FAN

AUTO

SETPOINT

After the desired setpoint is reached, the HOME screen will
reappear after about 8 seconds.

64

Figure 8

SYSTEM

HEAT

Page 3

Fan Control

Filter Reminder

The FAN button is located behind the small door on the
right-hand side of the thermostat. See figure 3. The FAN
button can be used to select either continuous fan mode or
auto fan mode.

If continuous fan mode is enabled, the fan will run continu­ously regardless of whether the heating or cooling equip­ment is running. Also, ON will be displayed in the FAN box
as shown in figure 9.

Fan ON with Icon

ROOM

73

FAN
ON

SYSTEM

HEAT

Figure 9

If auto fan mode is selected, the fan will only run when the
heating or cooling equipment is running. In this case, AUTO
will be displayed in the FAN box as shown in figure 10.

Fan AUTO with Icon

ROOM

73

FAN

The 51M32 thermostat includes a filter reminder feature.
The filter reminder can be set for 1, 3, 6, or 12−month inter­vals. The SETTINGS button, located behind the door on
the right−hand side of the thermostat is used to set the filter
reminder interval. See figure 3. Press the SETTINGS but­ton from the HOME screen to display the Filter Reminder
Settings screen as shown in figure 11.

Filter Reminder Settings

Filter

0

Figure 11

The default setting for the filter reminder is 0, which dis­ables the function. Use the UP arrow while in the Filter Re­minder Settings screen to select the desired interval be­tween reminders. It may be necessary to press the UP
arrow several times to access the desired setting. The
HOME screen will reappear about 10 seconds after the ar­row key has been pressed for the final time.

After the programmed interval has elapsed, the FILTER re­minder will be displayed as shown in figure 12. 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 timer has been reset.

Display of Filter Reminder

AUTO

SYSTEM

HEAT

Figure 10

To change from continuous to auto fan mode and vice versa,
press the FAN button. Also note the presence of a fan icon in
the FAN box. This icon indicates that the fan is running.

Page 4

ROOM

FILTER

72

FAN

AUTO

SYSTEM

HEAT

Figure 12

Service Indicator

Technical Specifications

When abnormal equipment operation is detected, the
SERVICE indicator will flash on the upper-right corner of
the screen. This indicates that the equipment requires ser­vice from a qualified service technician. The SERVICE indi­cator is shown in figure 13.

Service Indicator Flashing

ROOM

SERVICE

73

FAN

AUTO

SYSTEM

HEAT

Figure 13

Thermostat RESET

Under some abnormal conditions, it may be desirable to
reset" the thermostat to its default condition. This can be
useful on rare occasions when the the thermostat is behav­ing abnormally (e.g. after an electrical storm or power out­age). The RESET button can be used to recover from this
situation.

The RESET button is an unlabeled, recessed button lo­cated behind the door on the right−hand side of the thermo­stat, just below the SETTINGS button. The RESET button
is visible in figure 3. Use a paper clip or small pencil to press
the RESET button. After the RESET button is pressed, the
thermostat settings will return to the defaults listed in the
Default Settings section.

Default Thermostat Settings

Default thermostat settings are in table 1.

Table 1

Default Thermostat Settings

Mode Heat

Setpoint 70°F (or 21°C)

Fan Auto

Filter Reminder OFF (reminder setting = 0)

Equipment Protection
Timers

reset back to zero

Thermostat Type

Electronic nonprogrammable thermostat for 1H/1C, gas or
electric heat, non−heat pump, non−power robbing applica­tions.

Power Supply Range

18VAC − 30VAC (24VAC nominal), 60Hz

Temperature Display

Display Scale: Fahrenheit or Celsius user selectable (via
DIP switches)
Display range: 35°F (2°C) to 99°F (37°C)
Display resolution: 1°F (1°C)
Display Accuracy: +/−1°F

Temperature Measurement Range

Measurement Scale: Fahrenheit
Measurement Range: 35°F to 99°F
Measurement Resolution: 0.5°F
Measurement Accuracy: +/−1°F
Field Offset: via DIP switches to +/−3°F
Sampling Method: temperature measurements sampled
every 15 seconds. Displayed temperature is the average of
the last four measurements.

Temperature Setpoint Range

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

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.

1. HEAT/COOL relay output

2. FAN relay output

3. SERVICE relay input

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 min­utes.

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

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

Page 5