Honeywell Q674L Thermostat User Manual

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T874R Thermostats and Q674L Subbases  
Installation Instructions for the Trained Service Technician.  
INSTALLATION INSTRUCTIONS  
APPLICATION  
The T874R Thermostat and Q674L Subbase provide 24 to 30 Vac control of 2-stage heating and 1-stage cool-ing heat  
pump systems with manual changeover. Q674L Subbase provides EM.HT.-HEAT-OFF-COOL system switching and  
AUTO-ON fan switching. See Table 1 for specific T874R/Q674L combinations.  
Table 1. Thermostat/Subbase Specifications.  
Thermostat/  
Thermostat/  
Subbase  
Package  
Subbase  
Model  
Numbers  
LED  
Indication  
See  
Fig.  
Changeover  
Comments  
Y594R1243  
T874R1152/  
Q674L1207  
AUX.HT.,  
EM. HT.  
Manual Cool  
TRADELINE®; adjustable stage 2  
heat anticipation. Fixed anticipation  
in stage 1. Auto fan in EM.HT.  
6
Y594R1300  
Y594R1425  
T874R1475/  
Q674L1520  
AUX.HT.,  
EM. HT.a  
Manual Heat  
or Cool  
TRADELINE®; fixed heat  
anticipation. Auto fan in EM.HT.  
7
8
T874R1616/  
Q674L1587  
AUX.HT.,  
EM. HT.,  
CHECK  
Manual Heat  
or Cool  
SUPER TRADELINE®; fixed heat  
anticipation. Factory installed jumper  
across W1 and Y1. Auto fan in  
EM.HT.  
Y594R1615  
T874R1822/  
Q674L1710  
AUX.HT.,  
EM. HT.,  
CHECK  
Manual Heat  
or Cool  
TRADELINE®; fixed heat  
anticipation. Auto fan in EM.HT.  
10  
Y594R1664  
Y594R1672  
T874R1871/  
Q674L1736  
EM. HT.  
Manual Cool  
Manual Cool  
TRADELINE®; exact replacement  
for York model no. 2TH11702224.  
TRADELINE®; exact replacement  
for York model nos. 2TH11702324  
and 6TH11702224.  
9
T874R1889/  
Q674L1736  
EM. HT.  
11  
b
T874R1905/  
Q674L1777  
EM. HT.  
EM. HT.  
Manual Cool  
®
11  
Y594R1698  
TRADELINE ; exact replacement  
for York model nos. 2TH11702324  
and 6TH11702224. Includes  
C815A1054 Outdoor Thermistor.  
b
T874R1913/  
Q674L1777  
Manual Cool  
Manual Cool  
®
9
5
Y594R1706  
TRADELINE ; exact replacement  
for York model no. 2TH11702224.  
Y594R1763  
Y594R1797  
T874R1954/  
Q674L1827  
AUX.HT.,  
EM. HT.a  
Requires C815A Outdoor Thermister  
for outdoor reset. Fixed stage 1 heat  
anticipation. No heat anticipation in  
stage 2 heat. Auto fan in EM.HT.  
Replaces Y594R1136.  
T874R1988/  
Q674L1868  
AUX.HT.,  
EM.HT.  
Manual Heat  
or Cool  
TRADELINE®  
12  
a
b
EM.HT. LED also shows compressor malfunction.  
Premier White® color.  
®
U.S. Registered Trademark  
Copyright © 1997 Honeywell Inc. •  
All Rights Reserved  
69-0392-9  
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T874R THERMOSTATS AND Q674L SUBBASES  
OPERATION  
On a 2-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.  
CAUTION  
1. Disconnect power supply to prevent electrical  
shock or equipment damage.  
2. To prevent interference with the thermostat  
linkage, keep wire length to a minimum and  
run wires as close as possible to the subbase.  
3. Push excess wire back into the hole and plug  
hole to prevent drafts from affecting thermo-  
stat operation.  
4. Do not overtighten thermostat captive  
mounting screws because damage to  
subbase threads can result.  
5. Do not short across coil terminals on heating  
relay or gas valve. This can burn out the  
thermostat heat anticipator.  
There is about 1° F (0.6° C) between stages so the sec-  
ond stage makes only when the first stage can not handle  
the load. The 1° F (0.6° C) is referred to as the interstage  
differential.  
The light emitting diodes (LED) on the subbase light when  
something specific happens within the system. When an  
LED lights, refer to this list for the meaning:  
EM. HT.: Emergency heat is operating. The compres-  
sor has failed, and the heat pump is not operating.  
LED lights when system switch is placed in the  
EM.HT. position by the homeowner.  
AUX.HT.: Auxiliary heat is operating, which means the  
weather is so cold that the heat pump cannot handle  
the load.  
6. Never install more than one wire per terminal  
unless factory-supplied jumper with spade  
terminals is used.  
IMPORTANT  
Thermostats are calibrated at the factory using  
subbase mounted at true level. Inaccurate  
subbase leveling causes the actual temperature  
to deviate from the setpoint temperature.  
CHECK: System needs to be checked. See heating  
sys-tem instructions for specific meaning.  
NOTE: LEDs are not field replaceable or addable.  
Location  
Install the thermostat about 5 ft (1.5m) above the floor in  
an area with good air circulation at average temperature.  
Do not install the thermostat where it can be affected by:  
RECYCLING NOTICE  
This control contains mercury in a sealed tube. Do not  
place control in the trash at the end of its useful life.  
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.  
If this control is replacing a control that contains  
mer-cury in a sealed tube, do not place your old  
control in the trash.  
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.  
Mounting The Subbase  
The thermostat subbase can be mounted on a vertical  
outlet box, horizontal outlet box or directly on the wall.  
1.  
If you must mount the subbase on a vertical outlet  
box, order Honeywell 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.  
INSTALLATION  
For a wall installation, hold subbase in position and  
mark holes for anchors. See Fig. 2. Obtain wall  
anchors locally. Be careful that the wires do not fall  
back into the wall opening. Set aside subbase. Drill  
two 3/16 in. (5 mm) holes and gently tap anchors  
into the holes until flush with the wall.  
When Installing this Product…  
1.  
Read these instructions carefully. Failure to follow  
them could damage the product or cause a hazard-  
ous condition.  
2.  
Check the ratings given in the instructions and on  
the product to make sure the product is suitable for  
your application.  
3
.
.
Installer must be a trained, experienced service  
technician.  
After installation is complete, check out product  
operation as provided in these instructions.  
4
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T874R THERMOSTATS AND Q674L SUBBASES  
VERTICAL  
OUTLET  
4
.
Secure the cover plate (if used) and subbase with  
the screws provided. Do not fully tighten the  
subbase screws.  
BOX  
1
COVER  
PLATE  
ADAPTER  
2
5. Level the subbase by using a spirit level. Firmly  
tighten subbase mounting screws. See Fig. 3. The  
subbase mounting holes provide for minor out-of-  
level adjustments.  
RING  
2
IMPORTANT  
MOUNTING  
SCREWS (2)  
An incorrectly leveled subbase causes the  
temperature control to deviate from setpoint.  
Wiring the Subbase  
SUBBASE  
All wiring must comply with local electrical codes and  
ordinances. Follow equipment manufacturer wiring  
instructions when available. To wire subbase, proceed as  
follows:  
MOUNTING  
SCREWS (2)  
1.  
Connect the system wires to the subbase. See Fig.  
-12. A letter code for identification is located near  
5
HORIZONTAL  
OUTLET  
BOX  
MOUNTING  
SCREWS (2)  
each terminal. The terminal barrier permits straight  
or conventional wraparound wiring connection. See  
Fig. 4.  
1
SUBBASE  
2.  
Firmly tighten each terminal screw.  
1
2
NOT INCLUDED WITH UNIT.  
ACCESSORY PARTS AVAILABLE (193121A).  
3. Fit wires as close as possible to the subbase. Push  
excess wire back into the hole.  
M925  
4.  
Plug the hole with nonflammable insulation to  
prevent drafts from affecting the thermostat.  
Fig. 1. Installation of subbase on outlet box.  
TOP  
WIRING  
THERMOSTAT  
MOUNTING  
HOLES (2)  
TERMINAL  
CABLE OPENING  
SPIRIT LEVEL  
WALL  
WIRES THROUGH  
WALL OPENING  
WALL  
MOUNTING  
HOLES (2)  
POST (2) FOR  
MOUNTING  
THERMOSTAT  
TO SPRING FINGER  
CONTACTS ON THE  
THERMOSTAT  
ANCHORS  
2)  
MOUNTING  
HOLES  
(
(UP TO 12)  
M927  
Fig. 3. Subbase components and leveling procedure.  
MOUNTING  
SCREWS (2)  
M926  
SUBBASE  
FOR STRAIGHT  
INSERTION–  
STRIP 5/16 IN. (8 MM)  
FOR WRAPAROUND–  
STRIP 7/16 IN. (11 MM)  
Fig. 2. Installation of subbase on wall.  
2
3
.
.
Run wires to the thermostat location.  
Pull wires through the cover plate (if used) and sub-  
base cable opening. See Fig. 3.  
BARRIER  
SUBBASE TERMINAL SCREW  
IMPORTANT  
Use 18 gauge, color-coded thermostat cable for  
proper wiring.  
M928  
Fig. 4. Wiring connections.  
3
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T874R THERMOSTATS AND Q674L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
FAN RELAY  
1
G
W
2
AUX. HEATER  
RELAY  
AUX. HT.  
LED (GREEN)  
2
AUTO  
ON  
U
B
H1  
C1  
COMPRESSOR  
MONITOR  
FALL  
3
4
5
6
FAN  
SWITCH  
EM. HT.  
LED (RED)  
F
1
L1  
(
R
HOT)  
L2  
H2  
FALL  
SYSTEM  
SWITCH  
EM. HT.  
HEAT  
T
OUTDOOR  
THERMISTOR  
X2  
OFF  
OUTDOOR  
THERMOSTAT  
11  
COOL  
O
Y
COOL  
CHANGEOVER  
VALVE  
COMPRESSOR  
RELAY  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
M2970  
FIELD REMOVABLE JUMPER.  
Fig. 5. Internal schematic and typical wiring diagram for Y594R1763 (T874R1954/Q674L1827). Replaces  
GE AY28X078, AY28X139; Trane Baystat 139, Baystat 239 and Baystat 240;  
and Honeywell Y594R1136 Thermostats.  
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. 6. Internal schematic and typical wiring diagram for Y594R1243 (T874R1152/Q674L1207).  
69-0392—9  
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T874R THERMOSTATS AND Q674L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
L1  
HOT)  
L2  
(
ODT 1  
EHR 1  
1
2
RTD 2  
RTD 3  
H1/C1  
ANTICIAPTOR  
H1  
C1  
RTD 1  
FALL  
3
4
ODT 2  
EHR 2  
FAN  
SWITCH  
AUTO  
ON  
R
L
5
H2  
H2  
EM. HT.  
LED (RED)  
COMPRESSOR  
MONITOR  
ANTICIPATOR  
FALL  
6
X
AUX. HT.  
LED  
RTD 1  
(GREEN)  
W2  
8
SYSTEM  
SWITCH  
RD  
FAN RELAY  
EM. HT.  
HEAT  
G
10  
2
COOL  
CHANGEOVER VALVE  
OFF  
1
2
POWER SUPPLY. PROVIDE  
DISCONNECT MEANS AND  
OVERLOAD PROTECTION  
AS REQUIRED.  
O
E
EM. HT. RELAY  
COOL  
LACO  
CHP  
CONNECT CHANGEOVER  
RELAY TO B FOR HEAT  
CHANGEOVER, TO O FOR  
COOL CHANGEOVER.  
Y
B
COMPRESSOR  
CONTACTOR  
2
HEAT  
CHANGEOVER VALVE  
M1030A  
Fig. 7. Internal schematic and typical wiring diagram for Y594R1300 (T874R1475/Q674L1520); fixed anticipation.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
W3  
O
W3 RELAY  
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 wiring diagram for Y594R1425 (T874R1616/Q674L1587). SUPER  
®
TRADELINE ; universal model for heat, cool, or first stage heating changeover systems.  
CHECK LED has isolated terminals for use in all systems.  
5
69-0392—9  
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T874R THERMOSTATS AND Q674L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
L1 L2  
HOT)  
(
2
FAN SWITCH  
FALL  
C1  
H1/C1  
ANTICIPATOR  
1
FAN RELAY  
H1  
AUTO  
ON  
G
R
3
4
5
AUX. HT. RELAY  
W
FALL  
H
B
H2  
"
H" RELAY  
6
H2  
EM. HT.  
ANTICIPATOR  
SYSTEM  
SWITCH  
LED (RED)  
X
T
EM. HT.  
EM. HT. RELAY  
HEAT  
OFF  
C815A1039  
THERMISTOR  
O
COOL  
CHANGEOVER VALVE (COOL)  
Y
11  
RESET HEATER  
COMPRESSOR  
CONTACTOR  
12  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
M3173A  
Fig. 9. Internal schematic and typical wiring diagram for Y594R1664 (T874R1871/Q674L1736) and Y594R1706  
T874R1913/Q674L1777). Exact replacement for York model no. 2TH11702224.  
(
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
W3 RELAY  
W3  
O
L
COOL  
CHANGEOVER VALVE  
H1  
ANTICIPATOR  
1
CHECK  
LED (RED)  
COMPRESSOR  
MONITOR  
FAN  
SWITCH  
C ANTICIPATOR  
2
FAN RELAY  
G
R
AUTO  
ON  
1
L1  
(HOT)  
L2  
H1  
C
FALL  
W2  
E
3
4
SYSTEM  
SWITCH  
EM. HT.  
LED  
(RED)  
AUX. HT. RELAY  
AUX. HT.  
LED  
(GREEN)  
EM .HT.  
HEAT  
OFF  
EM. HT. RELAY  
5
X
B
H2  
ANTICIPATOR  
H2  
6
COOL  
HEAT  
FALL  
CHANGEOVER VALVE  
Y
1
1
COMPRESSOR  
RELAY  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
M5068  
Fig. 10. Internal schematic and typical wiring diagram for Y594R1615 (T874R1822/Q674L1710). TRADELINE;  
intended for use in applications where W2 and E terminals are not jumpered.  
69-0392—9  
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T874R THERMOSTATS AND Q674L SUBBASES  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
L1 L2  
HOT)  
(
2
3
FAN SWITCH  
FALL  
C1  
H1/C1  
ANTICIPATOR  
1
FAN RELAY  
H1  
AUTO  
ON  
G
R
4
5
AUX. HT. RELAY  
W
FALL  
H
B
H2  
"
H" RELAY  
6
H2  
EM. HT.  
ANTICIPATOR  
SYSTEM  
SWITCH  
LED (RED)  
X
T
EM. HT.  
HEAT  
EM. HT. RELAY  
C815A1039  
THERMISTOR  
OFF  
O
COOL  
CHANGEOVER VALVE (COOL)  
Y
11  
RESET HEATER  
COMPRESSOR  
CONTACTOR  
12  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
M3173A  
Fig. 11. Internal schematic and typical wiring diagram for Y594R1672 (T874R1889/Q674L1736) and Y594R1698  
T874R1905/Q674L1777). Exact replacement for York model nos. 2TH11702324 and 6TH11702224.  
(
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. 12. Internal schematic and typical wiring diagram for Y594R1797 (T874R1988/Q674L1868).  
7
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T874R THERMOSTATS AND Q674L SUBBASES  
1
.
Connect an ac ammeter of appropriate range  
between the heating terminals of the subbase:  
Stage 2: between W2 and R.  
Move the system switch to HEAT.  
After one minute, read the ammeter and record the  
reading:  
Stage 2: _______________amperes.  
After mounting the thermostat, set the adjustable  
heat anticipator to match the respective reading  
measured in step 3.  
Mounting the Thermostat  
1.  
Remove the thermostat cover by pulling the bottom  
edge of the cover away from the base until it snaps  
free from the cover clip.  
2
3
.
.
NOTE: The cover is hinged at the top and can be  
removed by pulling out at the bottom.  
4.  
2
.
.
Carefully remove and discard polystyrene packing  
insert that protects the mercury switches during  
shipment.  
If equipment cycles too fast, set the anticipator to a higher  
current rating, not more than one-half division at a time,  
and recheck cycle rate. Most conventional 2-stage heating  
equipment is designed to operate at 3 cycles per hour per  
stage. See Fig. 14.  
3
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 two tabs on the top inside edge of the  
thermostat base. The tabs fit into corresponding  
slots on the top of the subbase. Mount the thermo-  
stat on the subbase.  
Align the two captive mounting screws in the  
thermostat base with the posts on the subbase. See  
Fig. 13. Tighten both screws. Do not overtighten  
screws or damage to subbase posts can result.  
Hang the upper edge of the thermostat cover on top  
of the thermostat base and swing cover downward  
until it engages with the cover clip.  
4.  
5.  
6.  
Most heat pump systems should cycle 2-1/2 to 3 times  
per hour.  
THERMOSTAT  
MOUNTING SLOTS (2)  
THERMOSTAT  
1
.2.8  
MOUNTING POST (2)  
MOVE INDICATOR TO  
MATCH CURRENT RATING  
OF PRIMARY CONTROL  
M3684  
Fig. 14. Adjustable heat anticipator scale.  
0
0
7
8
0
6
HE  
AT  
50  
SUBBASE  
Temperature Setting  
Move the setpoint lever to the desired comfort position.  
One lever controls both heating and cooling.  
THERMOSTAT  
Subbase Setting  
CAPTIVE MOUNTING  
SCREWS (2)  
M3266  
System switching positions control thermostat operation as  
follows:  
Fig. 13. Mounting thermostat on subbase.  
OFF: Heating and cooling systems are off. If the fan  
switch is at the AUTO position, the cooling fan is  
also off.  
HEAT: Heating system is controlled by the thermostat.  
Cooling system is off.  
SETTINGS  
COOL: Cooling system is controlled by the thermostat.  
Heating system is off.  
EM.HT.: Emergency heat relay is energized on call for  
heat. Cooling system is off. Compressor is de-  
energized.  
CAUTION  
On systems using a gas valve, never apply a  
jumper across the valve coil terminals, even  
temporarily. This can burn out the thermostat heat  
anticipator(s).  
Fan switching positions control fan operation as follows:  
ON: Fan operates continuously.  
AUTO: Fan operates as controlled by the thermostat.  
Heat Anticipator Setting  
(2nd Stage Y594R1243)  
Set the heat anticipator scale to match the primary control  
current draw. When using a T874 Thermostat with two  
stages of heating, set the heat anticipator to match the  
respective primary control current draw. If the primary  
control nameplate has no rating or if further adjustment is  
necessary, use the following procedure to determine the  
current draw. Measure the current draw with the thermo-  
stat removed and the power on.  
To switch positions, use thumb and index finger to slide  
lever to desired position. Stop switch lever in detent  
directly over the desired function indicator mark for proper  
circuit operation.  
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T874R THERMOSTATS AND Q674L SUBBASES  
CHECKOUT  
CALIBRATION  
Heating  
Thermostat  
Move the system switch on the Q674 Subbase to HEAT.  
Move the setpoint lever on the T874 Thermostat about  
T874 Thermostats are accurately calibrated at the factory.  
There is no provision for field calibration.  
10° F (6° C) above room temperature. Both stages of  
heating and the fan should start. Move the setpoint lever  
about 10° F (6° C) below room temperature. Heating and  
fan should shut off.  
Thermometer  
The thermometer in the thermostat has been accurately  
calibrated at the factory. The thermometer should need  
adjustment only if it was dropped or shifted due to  
mishandling.  
NOTE: To prevent compressor short cycling, some  
manufacturer equipment includes a minimum-off  
timer to provide a five-minute time delay before  
turning on the compressor after the thermostat  
last turned off the compressor, or after the  
system first received power. This delay protects  
the compressor.  
If the setpoint lever and the thermometer reading do not  
agree:  
1
.
Remove the thermostat cover by pulling out from the  
bottom of cover until it clears the mounting slots.  
Set the thermostat cover on a table near an  
accurate thermometer.  
2.  
Cooling  
3. Allow 10 or 15 minutes for cover thermometer to  
sense area temperature; compare the readings. Be  
careful not to touch thermometer or breathe on it.  
4. If the readings are the same, replace cover and put  
the system into operation.  
5. If the readings are different, insert a small screw-  
driver into the thermometer and turn it until the  
thermometers have the same reading. See Fig. 15.  
6. Replace thermostat cover and put the system into  
operation.  
CAUTION  
Do not operate cooling if the outdoor temperature  
is below 50° F (10° C). Refer to manufacturer  
recommendations.  
Move the system switch on the Q674 Subbase to COOL.  
Move the setpoint lever on the T874 Thermostat about  
1
0° F (6° C) below room temperature. Cooling and fan  
should start (see NOTE above). Move the setpoint lever  
about 10° F (6° C) above room temperature. Cooling and  
fan should stop.  
NOTE: Radiant heat from hands offsets the thermometer  
reading. After making each adjustment, wait 10  
or 15 minutes for the thermometer to stabilize  
before comparing.  
Emergency Heat  
Move the system switch to EM.HT. The EM.HT. LED  
should come on. Move the setpoint lever about 10° F  
(
6° C) above room temperature. The electric strip heater(s)  
should come on. Move the setpoint lever about 10° F  
6° C) below room temperature. The electric strip heater  
(
should de-energize. The EM.HT. LED remains on until  
system switch is moved to another position.  
Fan  
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 con-  
trolled by the heating or cooling system.  
M5070  
Fig. 15. Thermometer calibration  
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Automation and Control Solutions  
Honeywell International Inc. Honeywell Limited—Honeywell Limitée  
1
985 Douglas Drive North  
35 Dynamic Drive  
Golden Valley, MN 55422  
Scarborough, Ontario M1V 4Z9  
69-0392—9 G.H. Rev. 10-97  
www.honeywell.com/yourhome  

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