Lennox 51M32 Thermostat User Manual

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OPERATION  
MANUAL  
®
2003 Lennox Industries Inc.  
Dallas, Texas, USA  
Merit® Series Thermostat  
CONTROLS (51M32)  
504,865M  
09/04  
Litho U.S.A.  
RETAIN THESE INSTRUCTIONS  
FOR FUTURE REFERENCE  
Table of Contents  
®
Merit  
Adjusting Temperature Setpoint . . . . . . . . . . . . . . . . . . 3  
Default Thermostat Settings . . . . . . . . . . . . . . . . . . . . . 5  
MeritR Series Thermostat  
®
The Lennox Merit Series Thermostat 51M32 is a nonpro-  
grammable electronic thermostat that is easy-to-use and  
has a large, easy-to-read display and excellent tempera-  
ture 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.  
Display − Initial Power−Up  
FILTER  
SERVICE  
ROOM  
General  
88  
These instructions are intended as a general guide and do  
not supersede local codes in any way. Consult authorities  
having jurisdiction before installation.  
FAN  
ON  
AUTO  
Check equipment for shipping damage. If you find any  
damage, immediately contact the last carrier.  
SYSTEM  
COOL  
OFF  
88  
SETPOINT  
Introduction  
EMG.  
HEAT  
This document describes the operation of Lennox thermostat  
51M32. Refer to the installation manual for instructions re-  
garding installation and wiring of the thermostat.  
Figure 1  
All display segments are momentarily activated. This oc-  
curs as a normal part of thermostat initialization. Within a  
(figure shows temperature in Fahrenheit units).  
Initial Thermostat Power-up  
When power is initially applied to the thermostat, the dis-  
Page 1  
 
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Display − Home Screen  
ROOM  
70  
Heat Mode Enabled  
ROOM  
69  
FAN  
FAN  
AUTO  
SYSTEM  
AUTO  
SYSTEM  
64  
SETPOINT  
HEAT  
HEAT  
Figure 2  
Figure 4  
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 indi-  
cated in the SYSTEM box at lower right).  
If the thermostat is in heat mode, heat mode is disabled  
when the HEAT button is pressed. This is indicated by OFF  
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.  
Heat Mode Disabled  
Heating Control  
ROOM  
69  
The HEAT button is located behind the small door on the  
right−hand side of the thermostat. See figure 3.  
FAN  
Additional Thermostat Buttons  
AUTO  
SYSTEM  
64  
SETPOINT  
OFF  
Figure 5  
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 thermo-  
stat will then activate the heating equipment to satisfy the de-  
mand. Heating operation is indicated by a flame icon in the  
SYSTEM box as shown in figure 6.  
Figure 3  
Enabling and Disabling Heat Mode  
Use the HEAT button to enable or disable heat mode as de-  
sired. 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.  
Page 2  
 
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Cooling Demand  
Heating Demand  
ROOM  
ROOM  
72  
79  
FAN  
FAN  
AUTO  
SYSTEM  
AUTO  
SYSTEM  
COOL  
88  
HEAT  
Figure 6  
Figure 7  
NOTE − The cooling equipment is activated for at least 4  
minutes if no buttons are pressed during the demand inter-  
val. Cooling equipment operation is locked out for 5 min-  
utes 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.  
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 inter-  
val.  
Adjusting Temperature Setpoint  
The temperature setpoint represents the desired tempera-  
ture of the space around the thermostat. The default tem-  
perature setpoint is 70°F. To adjust the setpoint, press the  
UP or DOWN arrow keys to the right of the display screen.  
Cooling Control  
The COOL button is located behind the small door on the  
right-hand side of the thermostat. See figure 3.  
The existing setpoint will be displayed just below the actual  
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.  
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 en-  
abled 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.  
Setpoint Display and Adjustment  
ROOM  
Cooling Demand  
69  
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.  
FAN  
AUTO  
SYSTEM  
64  
SETPOINT  
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.  
HEAT  
Figure 8  
After the desired setpoint is reached, the HOME screen will  
reappear after about 8 seconds.  
Page 3  
 
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Fan Control  
Filter Reminder  
The 51M32 thermostat includes a filter reminder feature.  
The filter reminder can be set for 1, 3, 6, or 12−month inter-  
vals. The SETTINGS button, located behind the door on  
the right−hand side of the thermostat is used to set the filter  
ton from the HOME screen to display the 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 continu-  
ously regardless of whether the heating or cooling equip-  
ment is running. Also, ON will be displayed in the FAN box  
Filter Reminder Settings  
Filter  
Fan ON with Icon  
0
ROOM  
73  
FAN  
ON  
SYSTEM  
HEAT  
Figure 11  
The default setting for the filter reminder is 0, which dis-  
ables the function. Use the UP arrow while in the Filter Re-  
minder Settings screen to select the desired interval be-  
tween 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 ar-  
row key has been pressed for the final time.  
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.  
After the programmed interval has elapsed, the FILTER re-  
minder will be displayed as shown in figure 12. After the fil-  
ter 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.  
Fan AUTO with Icon  
ROOM  
73  
Display of Filter Reminder  
FAN  
AUTO  
SYSTEM  
HEAT  
FILTER  
ROOM  
72  
FAN  
AUTO  
SYSTEM  
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.  
HEAT  
Figure 12  
Page 4  
 
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Service Indicator  
Technical Specifications  
Thermostat Type  
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 ser-  
vice from a qualified service technician. The SERVICE indi-  
Electronic nonprogrammable thermostat for 1H/1C, gas or  
electric heat, non−heat pump, non−power robbing applica-  
tions.  
Power Supply Range  
18VAC − 30VAC (24VAC nominal), 60Hz  
Service Indicator Flashing  
Temperature Display  
Display Scale: Fahrenheit or Celsius user selectable (via  
DIP switches)  
SERVICE  
ROOM  
73  
Display range: 35°F (2°C) to 99°F (37°C)  
Display resolution: 1°F (1°C)  
FAN  
Display Accuracy: +/−1°F  
AUTO  
Temperature Measurement Range  
Measurement Scale: Fahrenheit  
SYSTEM  
Measurement Range: 35°F to 99°F  
Measurement Resolution: 0.5°F  
Measurement Accuracy: +/−1°F  
HEAT  
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.  
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 behav-  
ing abnormally (e.g. after an electrical storm or power out-  
age). The RESET button can be used to recover from this  
situation.  
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).  
The RESET button is an unlabeled, recessed button lo-  
cated behind the door on the right−hand side of the thermo-  
stat, 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.  
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  
Default Thermostat Settings  
Minimum Compressor OFF time: 5 minutes  
Minimum Compressor ON time: 4 minutes  
Minimum Furnace ON time: 3 minutes  
Default thermostat settings are in table 1.  
Table 1  
Minimum furnace cycle time (elapsed time between any  
furnace activation and the next furnace activation): 6 min-  
utes.  
Default Thermostat Settings  
Mode  
Heat  
Minimum elapsed time between any compressor activation  
and the next compressor activation: 6 minutes.  
Setpoint  
Fan  
70°F (or 21°C)  
Auto  
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.  
Filter Reminder  
OFF (reminder setting = 0)  
Equipment Protection reset back to zero  
Timers  
Page 5  
 
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Equipment Protection Override  
Power Loss/Recovery  
Thermostat memory is retained for a minimum of 24 hours  
during a power loss (includes retention of programmed  
temperature setpoint, heat/cool and fan mode settings, fil-  
ter reminder status, and equipment protection timers). Af-  
ter 24 hours of power loss, programmed settings will be lost  
and replaced with default settings.  
Both the minimum compressor OFF timer and the mini-  
mum equipment cycle timer can be over−ridden by press-  
ing and holding either the HEAT or COOL button down for 4  
seconds.  
Over−Temperature Protection  
Thermal mechanical switch opens W1 at 93°F+/−6°F.  
Filter Reminder  
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.  
Settings of 0 (Off), 1, 3, 6 or 12 months are available. When  
programmed time has elapsed, a FILTER indicator is dis-  
played.  
Service Reminder  
LCD Backlight  
Activated for 8 seconds when any key is pressed.  
The SERVICE indicator is displayed only under the follow-  
ing conditions:  
NOTE − During an electrical storm or similar disturbance,  
the backlight may activate for a few seconds. This is normal  
and will no longer occur after the electrical disturbance has  
passed.  
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;  
Thermostat Operating Conditions  
35°F to 105°F, 5% to 90% RH  
OR  
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.  
Thermostat Storage Conditions  
−40°F to 185°F, 5% to 95% RH  
Thermostat Output Table  
The following table depicts the 51M32 thermostat output states for various input conditions. See table 2.  
Table 2  
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
X
X
X
X
cool demand  
X
X
X
no demand  
Electric Heat, Auto Fan  
heat demand  
X
X
cool demand  
no demand  
Electric Heat, Continuous Fan  
heat demand  
X
X
X
cool demand  
no demand  
NOTE −  
X = output is activated with 24VAC.  
Page 6  
 
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OPERATION  
MANUAL  
®
2003 Lennox Industries Inc.  
Dallas, Texas, USA  
Merit® Series Thermostat  
CONTROLS (51M33)  
504,931M  
09/04  
Litho U.S.A.  
RETAIN THESE INSTRUCTIONS  
FOR FUTURE REFERENCE  
Table of Contents  
®
Merit  
Adjusting Temperature Setpoint . . . . . . . . . . . . . . . . . . 3  
Default Thermostat Settings . . . . . . . . . . . . . . . . . . . . . 6  
MeritR Series Thermostat  
®
The Lennox Merit Series Thermostat 51M33 is a nonpro-  
grammable electronic thermostat that is easy-to-use and  
has a large, easy-to-read display and excellent tempera-  
ture 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 51M33 is suitable for heat pump, single−stage  
heat/single cool applications that are matched with a gas or  
electric furnace.  
Display − Initial Power−Up  
FILTER  
SERVICE  
ROOM  
General  
88  
These instructions are intended as a general guide and do  
not supersede local codes in any way. Consult authorities  
having jurisdiction before installation.  
FAN  
ON  
AUTO  
Check equipment for shipping damage. If you find any  
damage, immediately contact the last carrier.  
SYSTEM  
COOL  
OFF  
88  
SETPOINT  
Introduction  
EMG.  
HEAT  
This document describes the operation of Lennox thermostat  
51M33. Refer to the installation manual for instructions re-  
garding installation and wiring of the thermostat.  
Figure 1  
All display segments are momentarily activated. This oc-  
curs as a normal part of thermostat initialization. Within a  
(figure shows temperature in Fahrenheit units).  
Initial Thermostat Power-up  
When power is initially applied to the thermostat, the dis-  
Page 1  
 
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Enabling and Disabling Heat Mode  
Display − Home Screen  
ROOM  
70  
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 mode, normal heat mode is enabled  
when the HEAT button is pressed. This is indicated by  
FAN  
AUTO  
SYSTEM  
Normal Heat Mode Enabled  
ROOM  
HEAT  
69  
FAN  
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 indi-  
cated in the SYSTEM box at lower right).  
AUTO  
SYSTEM  
64  
SETPOINT  
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.  
HEAT  
Figure 4  
Heating Control  
If the thermostat is in normal heat mode when the HEAT  
button is pressed, then emergency heat mode is enabled.  
This is indicated by EMG. HEAT in the SYSTEM box as  
The HEAT button is located behind the small door on the  
right−hand side of the thermostat. See figure 3.  
Additional Thermostat Buttons  
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  
Emergency Heat Mode Enabled  
ROOM  
Figure 3  
69  
Normal Heat Mode  
FAN  
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.  
AUTO  
SYSTEM  
64  
SETPOINT  
Emergency Heat Mode  
EMG.  
HEAT  
In emergency heat mode, only the backup heat source is  
used to provide heat. The heat pump is disabled. The back-  
up heat source will be activated only when there is a heat  
demand.  
Figure 5  
Page 2  
 
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Enabling and Disabling Cool Mode  
Heat Mode Disabled  
Use the COOL button to enable or disable cool mode as  
necessary. If the thermostat is in off mode, cool mode is en-  
abled when the COOL button is pressed. This is indicated  
by COOL in the SYSTEM box.  
ROOM  
69  
FAN  
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.  
AUTO  
SYSTEM  
OFF  
64  
Cooling Demand  
SETPOINT  
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.  
Figure 6  
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 8.  
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.  
Heating Demand  
The thermostat must be in either normal or emergency  
heat mode in order to properly control the heating equip-  
ment. When in either heat mode, if the actual temperature is  
lower than the temperature setpoint, a heating demand is de-  
tected 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 7.  
Cooling Demand  
Heating Demand  
ROOM  
79  
FAN  
ROOM  
72  
AUTO  
FAN  
SYSTEM  
COOL  
AUTO  
SYSTEM  
88  
Figure 8  
HEAT  
NOTE − The cooling equipment is activated for at least 4  
minutes if no buttons are pressed during the demand inter-  
val. Cooling equipment operation is locked out for 5 min-  
utes 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.  
Figure 7  
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 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.  
Heat pump operation is locked out for 5 minutes after a de-  
mand has been satisfied. If another heat pump demand oc-  
curs during this 5−minute interval, the flame icon will flash;  
however, the heat pump will not run until the 5−minute delay  
has elapsed.  
Adjusting Temperature Setpoint  
The temperature setpoint represents the desired tempera-  
ture of the space around the thermostat. The default tem-  
perature 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  
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.  
Cooling Control  
The COOL button is located behind the small door on the  
right-hand side of the thermostat. See figure 3.  
Page 3  
 
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Fan AUTO with Icon  
Setpoint Display and Adjustment  
ROOM  
ROOM  
73  
69  
FAN  
FAN  
AUTO  
SYSTEM  
HEAT  
AUTO  
SYSTEM  
64  
SETPOINT  
HEAT  
Figure 11  
Figure 9  
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.  
After the desired setpoint is reached, the HOME screen will  
reappear after about 8 seconds.  
Filter Reminder  
The 51M33 thermostat includes a filter reminder feature.  
The filter reminder can be set for 1, 3, 6, or 12−month inter-  
vals. The SETTINGS button, located behind the door on  
the right−hand side of the thermostat is used to set the filter  
ton from the HOME screen to display the Filter Reminder  
Fan Control  
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.  
Filter Reminder Settings  
If continuous fan mode is enabled, the fan will run continu-  
ously regardless of whether the heating or cooling equip-  
ment is running. Also, ON will be displayed in the FAN box  
Filter  
0
Fan ON with Icon  
ROOM  
73  
FAN  
ON  
Figure 12  
The default setting for the filter reminder is 0, which dis-  
ables the function. Use the UP arrow while in the Filter Re-  
minder Settings screen to select the desired interval be-  
tween 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 ar-  
row key has been pressed for the final time.  
SYSTEM  
HEAT  
Figure 10  
After the programmed interval has elapsed, the FILTER re-  
minder will be displayed as shown in figure 13. After the fil-  
ter 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.  
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 11.  
Page 4  
 
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DOWN arrow keys to the right of the display screen. The  
balance point setting will increase by 1°F each time the UP  
key is pressed. The balance point setting will decrease by  
1°F each time the DOWN key is pressed.  
Display of Filter Reminder  
FILTER  
ROOM  
72  
After the desired balance point is reached, the HOME  
screen will reappear after about eight seconds.  
FAN  
AUTO  
SYSTEM  
NOTE − The balance point feature allows the temperature  
to rise or fall 3°F above or below the setpoint. This prevents  
excessive cycling of the equipment when the outdoor tem-  
perature is near the balance point. For example, if the bal-  
ance point is 40°F and the actual outdoor temperature is  
35°F, the outdoor temperature must rise to 43°F before  
equipment adjustment occurs. Conversely, if the balance  
point is 40°F and the actual outdoor temperature is 45°F,  
the outdoor temperature must drop to 37°F before equip-  
ment adjustment occurs.  
HEAT  
Figure 13  
Balance Point  
Service Indicator  
NOTE − The balance point is only available with the out-  
door sensor.  
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 ser-  
vice from a qualified service technician. The SERVICE indi-  
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.  
Service Indicator Flashing  
Use the SETTINGS button to access the balance point set-  
ting. If the outdoor sensor is attached to the thermostat,  
press the SETTINGS button twice to access the Balance  
SERVICE  
ROOM  
73  
FAN  
AUTO  
Balance Point Setting  
SYSTEM  
6P  
HEAT  
Figure 15  
Thermostat RESET  
Under some abnormal conditions, it may be desirable to re-  
set the thermostat to its default condition. The RESET but-  
ton can be used to return the unit to normal operation after  
an occurrence such as an electrical storm or power outage.  
SETPOINT  
55  
Figure 14  
The RESET button is an unlabeled, recessed button lo-  
cated behind the door on the right−hand side of the thermo-  
stat, 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.  
The balance point can be set at any temperature between  
1°F and 55°F (−17°C to 13°C). 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 55°F.  
To adjust the balance point up or down, press the UP or  
Page 5  
 
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Table 2  
Default Thermostat Settings  
Default Thermostat settings are in table 1.  
Table 1  
51M33 Terminal Designations  
Connections Description  
O
B
Reversing valve, cool active  
Reversing valve, heat active  
24VAC  
Default Thermostat Settings  
Mode  
Heat  
R
Setpoint  
Fan  
70°F (or 21°C)  
Auto  
G
Y1  
Fan control  
First stage cooling/heating, compres-  
sor generated  
Filter Reminder  
OFF (reminder setting = 0)  
Equipment Protection reset back to zero  
Timers  
W1  
L
Auxiliary heating, furnace generated  
Service Indicator  
C
24VAC common  
Technical Specifications  
E
Emergency heat  
Thermostat Type  
Electronic nonprogrammable thermostat for 1H/1C, heat  
pump with electric or gas backup heat source, non−power  
robbing applications.  
T
Outdoor temperature sensor  
connection 1  
T
Outdoor temperature sensor  
connection 2  
Power Supply Range  
18VAC − 30VAC (24VAC nominal), 60Hz  
Equipment Protection Timers  
Temperature Display  
Display Scale: Fahrenheit or Celsius user selectable (via  
DIP switches)  
Minimum Compressor OFF time: 5 minutes  
Minimum Compressor ON time: 4 minutes  
Minimum Furnace ON time: 3 minutes  
Display range: 35°F (2°C) to 99°F (37°C)  
Display resolution: 1°F (1°C)  
Minimum backup furnace cycle time (elapsed time be-  
tween any furnace activation and the next furnace activa-  
tion): 6 minutes.  
Display Accuracy: +/−1°F  
Temperature Measurement Range  
Measurement Scale: Fahrenheit  
Minimum elapsed time between any compressor activation  
and the next compressor activation: 6 minutes.  
Measurement Range: 35°F to 99°F  
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.  
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.  
Equipment Protection Override  
Both the minimum compressor OFF timer and the mini-  
mum equipment cycle timer can be over−ridden by press-  
ing and holding either the HEAT or COOL button down for 4  
seconds.  
Temperature Setpoint Range  
Setting range: 50°F (10°C) to 90°F (32°C)  
Setting resolution: 1°F (1°C)  
Over−Temperature Protection  
Fan Control  
AUTO or ON modes.  
Thermal mechanical switch opens W1 at 93°F+/−6°F.  
Filter Reminder  
Backup Heat Source Selection  
Electric or gas furnace, selectable via DIP switch #5 (Aux or  
Dual, respectively). See also Thermostat Output section.  
Settings of 0 (Off), 1, 3, 6 or 12 months are available. When  
programmed time has elapsed, a FILTER indicator is dis-  
played.  
I/O Relays  
All thermostat relays are latching type to minimize power  
consumption. See table 2.  
Balance Point  
0°F (OFF) to 55°F, user selectable.  
Page 6  
 
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Service Reminder  
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.  
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;  
LCD Backlight  
Activated for 8 seconds when any key is pressed.  
OR  
NOTE − During an electrical storm or similar disturbance,  
the backlight may activate for a few seconds. This is normal  
and will no longer occur after the electrical disturbance has  
passed.  
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.  
Thermostat Operating Conditions  
35°F to 105°F, 5% to 90% RH  
Power Loss/Recovery  
Thermostat memory is retained for a minimum of 24 hours  
during a power loss (includes retention of programmed  
temperature setpoint, heat/cool and fan mode settings, fil-  
ter reminder status, and equipment protection timers). Af-  
ter 24 hours of power loss, programmed settings will be lost  
and replaced with default settings.  
Thermostat Storage Conditions  
−40°F to 185°F, 5% to 95% RH  
Thermostat Output Table  
Table 3 (see page 8) provides details of the 51M33 ther-  
mostat output states for various input conditions.  
Page 7  
 
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Table 3  
Thermostat Output States  
Condition  
W1  
Y1  
G
O
E
Electric Heat Backup − No Outdoor Sensor  
small heat demand  
X
X
X
X
X
X
large heat demand  
emergency heat demand  
cool demand  
X
X
X
X
no demand  
dc  
Gas Heat Backup (Dual Fuel) − No Outdoor Sensor  
small heat demand  
large heat demand  
emergency heat demand  
cool demand  
X
X
X
X
X
X
X
X
X
no demand  
dc  
Electric Heat Backup − Outdoor Sensor Attached  
small heat demand (BBP)  
X
X
X
X
X
X
X
X
X
X
large heat demand (BBP)  
small heat demand (ABP)  
large heat demand (ABP)  
emergency heat demand  
cool demand  
X
X
X
no demand  
dc  
Gas Heat Backup (Dual Fuel) − Outdoor Sensor Attached  
small heat demand (BBP)  
large heat demand (BBP)  
small heat demand (ABP)  
large heat demand (ABP)  
emergency heat demand  
cool demand  
X
X
X
X
X
X
X
X
no demand  
dc  
NOTE −  
X = output is activated with 24VAC  
dc: does not care (output can be in either state, i.e., either active or inactive)  
BBP: outdoor temperature is below balance point  
ABP: outdoor temperature is above balance point  
small heat demand: temperature is between (setpoint − 1.5°F) and (setpoint − 0.5°F), and 30-minute upstage  
timer has not expired (see Normal Heat Mode graph)  
large heat demand: temperature is below (setpoint − 1.5°F), or 30-minute upstage timer has expired (see Nor-  
mal Heat Mode graph)  
the state of the B terminal is opposite the state of the O terminal.  
data above are tabulated for AUTO fan setting. If fan setting is ON, the fan is activated in all cases.  
Page 8  
 

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