Honeywell T874G Thermostat User Manual

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T874G,R Multistage Heat Pump Thermostats  
and Q674F,J,L Subbases  
INSTALLATION INSTRUCTIONS  
APPLICATION  
The T874G,R Thermostats with Q674F,J,L Subbases  
provide 24 to 30 Vac control of a two-stage heating/one-  
stage cooling heat pump system. See Table 1 for  
thermostat/subbase specifications.  
Table 1. Thermostat/Subbase Specifications.  
Switching  
Thermostat/Subbase  
T874G/Q674F  
System  
Fan  
Changeover  
Auto and Manual  
Auto  
OFF-EM.HT.-HEAT-AUTO-COOL  
EM.HT.-AUTO-OFF  
AUTO-ON  
AUTO-ON  
AUTO-ON  
T874G/Q674J  
T874R/Q674L  
EM.HT.-HEAT-OFF-COOL  
Manual  
OPERATION  
On a two-heat thermostat, the two stages of heat make  
sequentially as the temperature drops. Make refers to the  
mercury switch initiating a call for heat or cool.  
RECYCLING NOTICE  
This control contains mercury in a sealed tube. Do  
not place the control in the trash at the end of its  
useful life.  
If this control is replacing a control that contains  
mercury in a sealed tube, do not place your old  
control in the trash.  
There are about 2°F (1°C) between stages so that the  
second stage makes only when the first stage cannot  
handle the load. This is the interstage differential.  
Contact your local waste management authority for  
instructions regarding recycling and the proper  
disposal of this control, or of an old control  
containing mercury in a sealed tube.  
LEDs (light emitting diodes) are included on your subbase.  
Refer to the list below for specific meaning.  
The CHECK LED lights when something needs to be  
checked or done to maintain efficient operation of the  
system. See your heating system instructions for the  
specific meaning.  
The SYSTEM LED lights when the system is calling for  
heating or cooling.  
INSTALLATION  
The AUX. HT. LED lights when the auxiliary heat (second  
stage) is operating. Auxiliary heat operates when the heat  
pump alone cannot handle the load.  
When Installing this Product…  
1. Read these instructions carefully. Failure to follow  
them could damage the product or cause a  
hazardous condition.  
2. Check the ratings given in the instructions and on  
the product to make sure the product is suitable for  
your application.  
The EM. HT. LED lights when the system switch is placed  
in the EM. HT. position. Emergency heat is operating; in  
most systems, the compressor has failed and the heat  
pump is not operating.  
3.  
Installer must be a trained, experienced service  
technician.  
LEDs are not field replaceable or addable.  
4.  
After installation is complete, check out product  
operation as provided in these instructions.  
Copyright © 1995 Honeywell Inc. •  
• All Rights Reserved  
69-0268-11  
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
³
If you must mount the subbase on a vertical outlet  
box, order part no. 193121A Adapter Assembly. See  
Fig. 1. The assembly includes an adapter ring, two  
screws, and a cover plate to cover marks on the  
wall. Install the ring and cover plate on the vertical  
outlet box.  
CAUTION  
1
.
.
Disconnect power supply to prevent electrical  
shock or equipment damage.  
2
Run wires as close as possible to the  
subbase. To prevent interference with the  
thermostat linkage, keep wire length to a  
minimum. Push excess wire back into the hole  
and plug the hole to prevent drafts from  
affecting the thermostat operation.  
For a wall installation, hold the subbase in position and  
mark holes for the anchors. See Fig. 2. Obtain wall  
anchors locally. Take care that the wires do not fall back  
into the wall opening. Set aside the subbase. Drill four  
3
.
.
Do not overtighten the thermostat captive  
mounting screws because damage to the  
subbase threads can result.  
Do not short across coil terminals on relay;  
this can burn out the heat anticipator.  
3
/16 in. (5 mm) holes and gently tap anchors into the  
holes until flush with the wall.  
4
WALL  
Location  
WIRES THROUGH  
WALL OPENING  
Install the thermostat about 5 ft (1.5m) above the floor in  
an area with good circulation at room temperature.  
Do not install the thermostat where it can be affected by:  
drafts, or dead spots behind doors and in corners.  
hot or cold air from ducts.  
radiant heat from sun or appliances.  
concealed pipes and chimneys.  
unheated (uncooled) areas such as an outside wall  
behind the thermostat.  
WALL  
ANCHORS  
(2)  
MOUNTING  
HOLES  
Mounting the Subbase  
MOUNTING  
SCREWS (2)  
M926  
SUBBASE  
The thermostat subbase can be mounted on a vertical  
outlet box, horizontal outlet box, or directly on the wall.  
Fig. 2. Installation of subbase on wall.  
VERTICAL  
OUTLET  
BOX  
1
·
»
Pull wires through the cover plate (if used) and  
subbase cable opening. See Fig. 12.  
Secure the cover plate (if used) and subbase with  
the screws provided. Do not fully tighten the  
subbase screws.  
COVER  
PLATE  
ADAPTER  
2
RING  
2
¿
Level the subbase using a spirit level, as shown in  
Fig. 11, and firmly tighten the subbase mounting  
screws. The subbase mounting holes provide for  
minor out-of-level adjustments.  
MOUNTING  
SCREWS (2)  
IMPORTANT  
An incorrectly leveled subbase will cause the  
temperature control to deviate from setpoint.  
SUBBASE  
MOUNTING  
SCREWS (2)  
Wiring the Subbase  
All wiring must comply with local electrical codes and  
ordinances. Follow the equipment manufacturer wiring  
instructions when available. To wire the subbase, proceed  
as follows:  
HORIZONTAL  
OUTLET  
BOX  
MOUNTING  
SCREWS (2)  
1
³
Connect system wires to the subbase. See Fig. 3  
through 11. A letter code is located near each  
terminal for identification. The terminal barrier  
permits straight or conventional wraparound wiring  
connection (Fig. 13).  
SUBBASE  
1
2
NOT INCLUDED WITH UNIT.  
ACCESSORY PARTS AVAILABLE (193121A).  
M925  
·
»
Firmly tighten each terminal screw.  
Fit wires as close as possible to the subbase. Push  
excess wire back into the hole.  
Fig. 1. Installation of subbase on outlet box.  
¿
Plug the hole with nonflammable insulation to  
prevent drafts from affecting the thermostat.  
69-0268—11  
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
1
O
G
FALL  
H1  
FAN SWITCH  
H1 ANTICIPATOR  
COOL CHANGEOVER  
VALVE  
AUTO  
ON  
2
FAN RELAY  
B
3
B RELAY  
W3  
4
6
AUX HT. RELAY  
L1  
R
(HOT)  
SYSTEM  
SWITCH  
L2  
H2  
E
L
1
ANTICIPATOR  
OFF  
EM. HT. RELAY  
H2 FALL  
EM. HT.  
HEAT  
EM. HT.  
LED (RED)  
AUTO  
COOL  
2
X
RISE  
8
9
AUX. HT.  
LED (GREEN)  
C1  
AUX. HT. RELAY  
W2  
Y
C1 ANTICIPATOR  
RISE  
1
0
COMPRESSOR  
CONTACTOR  
1
1
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
CO  
12  
2
3
TERMINAL LABELED C/X ON SOME MODELS.  
W3 TERMINAL ON SOME MODELS ONLY.  
M5986A  
Fig. 3. Internal schematic and typical hookup for T874G/Q674F in heat pump system. Includes AUX. HT. and EM.  
HT. LEDs.  
3
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
COOL CHANGEOVER  
VALVE  
O
G
FAN  
SWITCH  
1
FAN RELAY  
L2  
H1  
H1  
AUTO  
ON  
ANTICIPATOR  
1
FALL  
L1  
(HOT)  
2
R
3R  
4
6
SEQ 2  
SEQ 1  
W1  
FALL  
AUX. HT.  
LED  
2
H2  
(YELLOW)  
E
H2 ANTICIPATOR  
SYSTEM  
SWITCH  
EM. HT.  
RELAY  
4R  
RISE  
CO  
X
C
EM. HT.  
AUTO  
OFF  
4R  
8
9
CHECK  
LED  
(RED)  
5R  
SYSTEM  
LED  
GREEN)  
10  
(
HPS  
4R  
C1  
ANTICIPATOR  
RISE  
Y
C1  
COMPRESSOR  
4R  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED. CONTACTOR  
M1629  
2
REMOVE JUMPER FOR INDEPENDENT CONTROL OF W1 AND E TERMINALS.  
Fig. 4. Internal schematic and typical hookup for T874G/Q674J in heat pump system. Includes AUX. HT., CHECK  
and SYSTEM LEDs.  
69-0268—11  
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
2
O
G
COOL  
CHANGEOVER VALVE  
FAN  
SWITCH  
H1  
C1  
AUTO  
ON  
FALL  
FAN RELAY  
L1  
(HOT)  
H1/C1  
ANTICIPATOR  
R
L2  
1
3
4
W1  
2
AUX. HT.  
LED  
EM. HT. RELAY  
(YELLOW)  
SYSTEM  
SWITCH  
5
6
E
X
COMPRESSOR  
FAILURE  
EM. HT.  
HEAT  
CHECK  
LED  
(RED)  
H2  
FALL  
H2 ANTICIPATOR  
OFF  
C
COOL  
11  
C815A OUTDOOR  
THERMISTOR  
SYSTEM  
LED (GREEN)  
RESET  
1
2
T
Y
COMPRESSOR  
CONTACTOR  
1
2
POWER SUPPLY. PROVIDE DISCONNECT  
MEANS AND OVERLOAD PROTECTION  
AS REQUIRED.  
M1628A  
FACTORY-INSTALLED JUMPER.  
Fig. 5. Internal schematic and typical hookup for T874R/Q674L in heat pump system with outdoor reset. Includes  
AUX. HT., CHECK and SYSTEM LEDs.  
5
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
2
O
FAN  
SWITCH  
COOL CHANGEOVER  
VALVE  
FALL  
C1  
FAN RELAY  
H1  
AUTO  
ON  
G
R
H1/C1  
ANTICIPATOR  
L1  
(HOT)  
3
4
1
L2  
3R  
W1  
SYSTEM  
SWITCH  
AUX. HT.  
LED  
(YELLOW)  
SEQ 1  
5
6
2
EM. HT.  
SEQ 2  
HEAT  
H2  
E
FALL  
H2  
OFF  
ANTICIPATOR  
EM. HT. RELAY  
4R  
COOL  
4R  
EM. HT.  
LED  
RED)  
(
X
C
SYSTEM  
LED  
C815A  
OUTDOOR  
THERMISTOR  
5R  
11  
HPS  
4R  
(GREEN)  
12  
T
Y
RESET  
COMPRESSOR  
CONTACTOR  
4R  
M1858  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
REMOVE JUMPER FOR INDEPENDENT CONTROL OF W1 AND E TERMINALS.  
Fig. 6. Internal schematic and typical hookup for T874R/Q674L in heat pump system with outdoor reset. Includes  
AUX. HT., EM. HT. and SYSTEM LEDs.  
L1  
HOT)  
L2  
(
H1  
2
3
4
C1  
H2  
H1/C1  
1
ANTICIPATOR  
FALL  
2
6.5 VAC  
TRANSFORMER  
AUTO  
ON  
R
ANTICIPATOR  
EM. HT. RELAY  
6
L
EMERGENCY  
HEAT  
(RED)  
X
AUXILIARY  
HEAT  
H2  
AUXILIARY  
EM. HT.  
HEAT  
OFF  
HEAT RELAY  
FALL  
(GREEN)  
W2  
G
FAN RELAY  
CHANGEOVER  
RELAY  
COOL  
O
E
EM. HT. RELAY  
COMPRESSOR  
RELAY  
1
POWER SUPPLY. PROVIDE  
DISCONNECT MEANS AND  
OVERLOAD PROTECTION  
AS REQUIRED.  
Y
B
B RELAY  
M6565  
Fig. 7. Internal schematic and typical hookup for T874R/Q674L in heat pump system. Includes EM. HT and AUX.  
HT. LEDs.  
69-0268—11  
6
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
W3 RELAY  
W3  
O
COOL CHANGEOVER  
VALVE  
L
COMPRESSOR  
MONITOR  
H1  
ANTICIPATOR  
FAN RELAY  
FAN  
SWITCH  
1
2
G
AUTO  
ON  
C ANTICIPATOR  
L1  
R
(HOT)  
L2  
1
H1  
W2  
C
3
EM. HT.  
LED (RED)  
AUX. HT. RELAY  
EM. HT. RELAY  
FALL  
SYSTEM  
SWITCH  
4
5
6
AUX. HT.  
LED (GRN)  
E
X
EM. HT.  
HEAT  
H2  
ANTICIPATOR  
H2  
OFF  
3
HEAT  
FALL  
X2  
CHANGEOVER  
VALVE  
COOL  
B
11  
W1 RELAY  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD  
PROTECTION AS REQUIRED.  
W1  
COMPRESSOR  
RELAY  
2
3
REMOVE JUMPER WHEN W1 RELAY IS USED.  
FACTORY-INSTALLED JUMPER.  
2
M5067  
Y
Fig. 8. Internal schematic and typical hookup for T874R/Q674L in heat pump system. Includes CHECK, EM. HT.  
and AUX. HT. LEDs.  
7
69-0268—11  
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
HOT) L1 L2  
(
1
H1/C1  
ANTICIPATOR  
R
FALL  
2
ODT 1  
EHR 1  
ODT 2  
H1  
RTD 1  
RTD 2  
C1  
W3  
3
4
FAN SWITCH  
AUTO  
ON  
EHR 2  
RTD 3  
RTD 1  
H2  
ANTICIPATOR  
W2  
5
6
AUX. HT.  
LED  
GREEN)  
(
H2  
2
FALL  
X
EM. HT.  
LED (RED)  
SYSTEM  
MONITOR  
SYSTEM  
SWITCH  
RD  
L
FAN RELAY  
G
O
EM. HT.  
HEAT  
OFF  
EM. HT.  
RELAY  
COOL CHANGEOVER  
VALVE  
E
COOL  
LACO  
CHP  
Y
B
COMPRESSOR  
CONTACTOR  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
AUXILIARY HEAT LED AVAILABLE ON SOME MODELS.  
M5072A  
Fig. 9. Internal schematic and typical hookup for T874R/Q674L in heat pump system. Includes EM. HT. and AUX.  
HT. LEDs and W3 terminal for additional heat stage.  
69-0268—11  
8
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
L1  
R
(HOT)  
L2  
1
L
2
EM. HT.  
H1/C1  
ANTICIPATOR  
LED (RED)  
AUX. HT.  
RELAY  
FAN  
3
3
SWITCH  
W3  
H1  
AUTO  
C1  
2
FALL  
FALL  
ON  
4
X
H2  
AUX. HT.  
LED (GRN)  
AUX. HT.  
RELAY  
ANTICIPATOR  
H2  
6
W2  
G
SYSTEM  
SWITCH  
FAN RELAY  
EM. HT.  
HEAT  
OFF  
COOL CHANGEOVER  
VALVE  
O
E
COOL  
EM. HT. RELAY  
Y
B
COMPRESSOR  
CONTACTOR  
"
B" RELAY  
1
2
3
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
M3683A  
TERMINAL LABELED C/X ON SOME MODELS.  
W3 TERMINAL AVAILABLE ON SOME MODELS ONLY.  
Fig. 10. Internal schematic and typical wiring diagram for T874R/Q674L in heat pump system. Includes EM. HT.  
and AUX. HT. LEDs.  
»
¿
´
Turn over the thermostat base and note the spring  
fingers that engage the subbase contacts. Make  
sure the spring fingers are not bent flat, preventing  
proper electrical contact with the subbase.  
Note the tabs along the top inside edge of the  
thermostat base. The tabs fit into the corresponding  
slots on the top of the subbase. Mount the  
thermostat on the subbase.  
Align the two captive mounting screws in the  
thermostat base with the posts on the subbase. See  
Fig. 14. Tighten both screws. Do not overtighten  
screws or damage to subbase can result.  
Mounting the Thermostat  
³
Remove the thermostat cover by pulling the bottom  
edge of the cover outward and away from the base  
until it snaps free of the retaining posts.  
NOTE: The cover is hinged at the top and must be  
removed by pulling the bottom edge  
outward and away from the base.  
·
Carefully remove and discard the polystyrene  
packing insert that protects the mercury switches  
during shipment.  
9
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
L1  
HOT) L2  
(
1
O
FALL  
CHANGEOVER  
RELAY  
H1  
FAN  
SWITCH  
C1  
G
R
H1/C1  
ANTICIPATOR  
AUTO  
ON  
FAN RELAY  
SEQ 2  
W
2
3R  
AUXILIARY  
HEAT  
LED  
SEQ 1  
(YELLOW)  
SYSTEM  
SWITCH  
E
X
C
T
EM. HT. RELAY  
EM. HT.  
HEAT  
4
R
FALL H2  
CHECK  
LED  
H2  
ANTICIPATOR  
OFF  
(RED)  
4R  
COOL  
SYSTEM  
LED  
(GREEN)  
5R  
HPS  
4R  
Y
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
REMOVE JUMPER FOR INDEPENDENT CONTROL OF W AND E TERMINALS.  
COMPRESSOR  
CONTACTOR  
4R  
M1627A  
Fig. 11. Internal schematic and typical hookup for T874R/Q674L in heat pump system. Includes AUX. HT., CHECK  
and SYSTEM LEDs.  
TOP  
MOUNTING  
HOLES (2)  
WIRING  
TERMINAL  
THERMOSTAT  
CABLE OPENING  
FOR STRAIGHT  
INSERTION–  
STRIP 5/16 in. (8 mm)  
FOR WRAPAROUND–  
STRIP 7/16 in. (11 mm)  
SPIRIT LEVEL  
BARRIER  
SUBBASE TERMINAL SCREW  
M928  
Fig. 13. Wiring connections.  
MOUNTING  
HOLES (2)  
POST (2) FOR  
MOUNTING  
THERMOSTAT  
TO SPRING FINGER  
CONTACTS ON THE  
THERMOSTAT  
(UP TO 12)  
M927  
Fig. 12. Subbase components and leveling procedure.  
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
Cooling  
THERMOSTAT  
MOUNTING SLOTS (2)  
CAUTION  
THERMOSTAT  
MOUNTING POST (2)  
Do not operate cooling if outdoor temperature is  
below 50°F (10°C). Refer to manufacturer  
recommendations.  
Move the system switch on the subbase to COOL. Move  
the setpoint lever (cooling lever on T874G) on the thermo-  
stat about 10°F (6°C) below the room temperature.  
Cooling and fan should start. Move the lever (cooling lever  
on T874G) about 10°F (6°C) above the room temperature.  
Cooling and fan should stop.  
50  
60 70 80  
HEAT  
SUBBASE  
THERMOSTAT  
CAPTIVE MOUNTING  
SCREWS (2)  
M3266  
Emergency Heat  
Move the system switch on the subbase to EM. HT. Move  
the setpoint lever (heating lever on T874G) about 10°F  
Fig. 14. Mounting thermostat on subbase.  
(6°C) above the room temperature. The electric strip  
heater(s) should come on. Move the lever (heating lever  
on T874G) about 10°F (6°C) below the room temperature.  
The electric strip heater should de-energize.  
SETTING  
Temperature Setting  
Fan  
The T874R has one setpoint lever that controls both  
heating and cooling. The T874G has one lever that  
controls heating and another lever that controls cooling.  
Move the setpoint lever(s) to the desired control  
position(s).  
Move the subbase system switch to OFF, and the fan  
switch to ON. The fan should run continuously. When the  
fan switch is in the AUTO position, fan operation is  
controlled by the heating or cooling system.  
Outdoor Reset Thermistor  
Subbase Setting  
Some systems are supplied with a Honeywell C815A1005  
Thermistor for outdoor mounting. The thermistor must be  
used; if not, thermostat performance will deviate radically  
from proper operation.  
System switching positions control thermostat operation as  
follows:  
EM. HT.: Emergency heating system is energized. Cooling  
system is off. Compressor is de-energized.  
HEAT: Heating system is controlled by the thermostat.  
Cooling system is off.  
OFF: Both the heating and cooling systems are off.  
COOL: Cooling system is controlled by the thermostat.  
Heating system is off.  
The proper thermistor operation must be verified to assure  
the correct operation of the thermostat. Check thermistor  
operation as follows:  
³
·
Disconnect the T wire on the subbase.  
Use an ohmmeter to measure resistance between  
the T wire and the transformer secondary common  
or C terminal.  
AUTO: Thermostat automatically changes between heat  
and cool modes depending on indoor temperature.  
»
¿
Take outdoor temperature at thermistor location  
and find the correct thermistor resistance on chart  
in Fig. 15.  
If the resistance measured in step 2 and the  
calculated resistance in step 3 vary by more than  
Fan switching positions control fan operation as follows:  
ON: Fan operates continuously.  
AUTO: Fan operates with equipment as controlled by the  
thermostat.  
1
5 percent, the thermistor requires replacement.  
To switch positions, use your thumb and index finger to  
slide the lever to the desired position. The switch lever  
must be set directly over the desired function indicator  
mark for proper circuit operation.  
Contact the installation dealer for an outdoor  
thermistor replacement.  
CALIBRATION  
CHECKOUT  
Thermostat  
These thermostats are accurately calibrated at the factory.  
They do not have provision for field calibration.  
Heating  
Move the system switch on the subbase to HEAT and the  
fan switch to AUTO. Move the setpoint lever (heating lever  
on T874G) on the thermostat about 10°F (6°C) above the  
room temperature. Heating and fan should start if there is  
no time delay or outdoor temperature limiting system.  
Move the lever (heating lever on T874G) about 10°F (6°C)  
below the room temperature. Heating and fan should shut  
off.  
Thermometer  
The thermometer in your thermostat has been accurately  
calibrated at the factory. The thermometer should only  
need adjustment if it has been dropped or jarred.  
1
1
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T874G,R MULTISTAGE HEAT PUMP THERMOSTATS AND Q674F,J,L SUBBASES  
If the setpoint lever setting and the thermometer reading  
do not agree, follow the procedure below.  
¿
Insert a small screwdriver in the thermometer shaft  
(Fig. 16) and turn it until the thermometers read the  
same. When the thermometer is calibrated, replace  
cover and place into operation.  
³
Remove thermostat cover by pulling the bottom  
edge of the cover outward and away from the base  
until it clears the retaining posts.  
·
»
Set the cover on a table near an accurate  
thermometer.  
After allowing five or ten minutes for stabilization,  
compare the readings. If they are the same, replace  
cover and put system into operation. If they are  
different, recalibrate the thermostat thermometer;  
see step 4.  
NOTE: Radiant heat from your hands will offset the  
thermometer reading. After making each  
adjustment, wait five or ten minutes for the  
thermometer to stabilize before comparing.  
4
4
4
4
3
3
3
3
3
2
2
2
2
2
1
1
1
1
1
600  
400  
200  
000  
800  
600  
400  
200  
000  
800  
600  
400  
200  
000  
800  
600  
400  
200  
000  
C815A THERMISTOR RESISTANCE  
R = 400 ohms ± 10% AT 77°F (25°C)  
800  
600  
400  
200  
0
-20  
0
20  
40  
60  
80  
100  
120  
140  
M5070  
TEMPERATURE OF THERMISTOR (°F)  
M1590A  
Fig. 15. Thermistor resistance chart.  
Fig. 16. Thermometer calibration.  
Home and Building Control  
Honeywell Inc.  
Home and Building Control  
Honeywell Limited-Honeywell Limitée  
35 Dynamic Drive  
1
985 Douglas Drive North  
Golden Valley, MN 55422  
Scarborough, Ontario M1V 4Z9  
69-0268—11 J.S. Rev. 12-95  
www.honeywell.com/yourhome  

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