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TRADELINE®  
T874G Thermostats  
and Q674F,J Subbases  
for Heat Pump Systems  
Installation Instructions for the Trained Service Technician.  
Application  
The T874G Thermostats and Q674F,J Subbases pro-  
vide 24 to 30 Vac control of 2-stage heating and 1-stage cool-  
ing heat pump systems with automatic changeover. Stage 1  
heat and cool anticipation is fixed voltage type; stage 2 heat  
anticipation is adjustable (except as noted). See Table 1 for  
specific T874G/Q674F,J combinations and specifications.  
TABLE 1—THERMOSTAT/SUBBASE SPECIFICATIONS.  
Thermostat/  
Subbase  
Model  
Thermostat/  
Subbase  
Package  
LED  
Indication  
Switching  
System  
See  
Fig.  
Numbers  
Fan  
Changeover  
Comments  
TRADELINE®  
Y594G1252  
—
T874G1246/  
Q674F1212  
AUX.HT.,  
EM.HT.  
EM.HT.-OFF-  
HEAT-AUTO-  
COOL  
AUTO-  
ON  
AUTO,  
COOL  
5
a
b
T874G1246/  
Q674F1410  
AUX.HT., EM.HT. -OFF- AUTO-  
AUTO,  
COOL  
Separate W1 and Y1  
terminals; TRADELINE  
subbase.  
6
7
a
®
EM.HT.  
HEAT-AUTO-  
COOL  
ON  
Y594G1419  
T874G1642/  
Q674F1444  
AUX.HT.,  
EM.HT.,  
CHECK  
OFF-EM.HT.-  
HEAT-AUTO-  
COOL  
AUTO-  
ON  
AUTO,  
HEAT OR  
COOL  
®;  
SUPER TRADELINE  
includes factory-installed  
jumper across W1 and Y1;  
fixed stage 2 heat anticipation.  
Isolated CHECK LED  
includes jumper for connecting  
X2 terminal to X or R for  
power.  
Y594G1476c  
T874G1741/  
Q674F1477  
Y594G1534d T874G1824/  
Q674F1477  
Y594G1526  
T874G1626/  
Q674F1436  
AUX.HT.,  
EM.HT.  
OFF-EM.HT.-  
HEAT-AUTO-  
COOL  
AUTO-  
ON  
AUTO,  
HEAT  
TRADELINE®  
8
9
(RED)e  
EM.HT.  
EM.HT.  
OFF-EM.HT.-  
HEAT-AUTO-  
COOL  
AUTO-  
ON  
AUTO  
TRADELINE subbase; exact  
®
—
T874D1165  
or  
T874E1016/  
Q674F1543  
replacement for York model  
no. 2TB04700524. Thermostat  
not included; order separately.  
®
Y594G1567  
T874G1865/  
Q674J1209  
EM.HT.-  
AUTO-OFF  
AUTO-  
ON  
AUTO,  
COOL  
TRADELINE ; exact  
10  
10  
11  
replacement for York model  
nos. 2TH11702424 and  
6TH11702424.  
Y594G1575c T874G1873/  
Q674J1225  
EM.HT.-  
AUTO-OFF  
AUTO-  
ON  
AUTO,  
COOL  
TRADELINE ; exact  
®
replacement for York model  
nos. 2TH11702424 and  
6TH11702424.  
Y594G1633  
T874G1972/  
Q674F1584  
AUX.HT.,  
EM.HT.  
OFF-EM.HT.-  
HEAT-AUTO-  
COOL  
AUTO-  
ON  
AUTO,  
HEAT OR  
COOL  
TRADELINE®  
a
b
c
d
e
EM.HT. also shows compressor malfunction.  
When switch is in EM. HT. position, the emergency heat will operate continuously until system switch is moved to another position.  
Thermostat is white and subbase is gray.  
Sold only in Australia; degrees C.  
LED indicator is not labeled but may be connected per user's requirements. See Fig. 9.  
J.H. • Rev. 7-94 •  
• ©Honeywell Inc. 1994 • Form Number 69-0435—10  
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IMPORTANT: Thermostats are calibrated at the factory by  
using subbases mounted at true level. Inaccurate sub-  
base leveling will cause thermostat control deviation.  
Operation  
On a 2-stage heating 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.  
There are about 2° F [1° C] between stages so the  
sec-ond stage makes only when the first stage cannot  
handle the load. This 2° F [1° C] is referred to as the  
interstage differential.  
The LED indicators are light emitting diodes on the  
subbase that light up when something specific happens  
within the system. When an LED lights up, refer to the  
following list for the meaning:  
LOCATION  
Install the thermostat about 5 ft [1.5 m] above the  
floor in an area with good air circulation at average  
temperature.  
Do not install the thermostat where it can be affected  
by:  
•
drafts, or dead spots behind doors and in cor-  
ners.  
•
•
•
•
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.  
EM.HT.: Emergency heat is operating, which means  
the system switch is at EM. HT.  
AUX.HT.: Auxiliary heat is operating, which means  
the weather is so cold that the heat pump can not  
handle the load alone.  
CHECK: System needs to be checked. See Heating/  
Cooling System Instructions for specific meaning.  
LEDs are not field replaceable or addable.  
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 193121A (beige) or 202689A (gray) Adapter  
Assembly. SeeFig. 1. Theassemblyincludesanadapterring,  
twoscrewsandacoverplatetocovermarksonthewall. Install  
the ring and cover plate on the vertical outlet box.  
For a wall installation, hold subbase in position and  
mark holes for anchors. See Fig. 2. Obtain wall anchors  
locally. Set subbase aside. Drill four 3/16 in. [5 mm] holes  
and gently tap anchors into the holes until flush with the wall.  
2. Run wires to the thermostat location. See wiring  
diagrams, Figs. 5-11.  
Recycling Notice  
This control contains mercury in a sealed tube. Do not  
place 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.  
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.  
Fig. 1—Installation of Q674 Subbase on outlet  
box.  
VERTICAL  
OUTLET  
1
Installation  
BOX  
COVER  
PLATE  
ADAPTER  
WHEN INSTALLING THIS PRODUCT…  
2
RING  
2
1
. Read these instructions carefully. Failure to  
follow them could cause a hazardous condition.  
. Check the ratings given in the instructions and on  
2
the product to make sure the product is suitable for your  
application.  
MOUNTING  
SCREWS (2)  
3
. Installer must be a trained, experienced service  
technician.  
4
. After installation is complete, check out product  
operation as provided in these instructions.  
SUBBASE  
MOUNTING  
SCREWS (2)  
CAUTION  
!
1
. Disconnect power supply to prevent electri-  
cal shock or equipment damage.  
HORIZONTAL  
2
. To prevent interference with the thermostat  
linkage, keep wire length to a minimum and  
run wires as close as possible to the subbase.  
. Do not overtighten thermostat captive mount-  
ing screws because damage to subbase threads  
can result.  
OUTLET  
BOX  
1
MOUNTING  
SCREWS (2)  
SUBBASE  
NOT INCLUDED WITH UNIT.  
3
1
2
ACCESSORY PARTS AVAILABLE (193121A).  
M925  
4
5
. Do not short across coil terminals on relay. This  
may burn out the thermostat heat anticipator.  
. Never install more than one wire per termi-  
nal unless factory-supplied jumper with spade  
terminal is used.  
6
9-0435—10  
2
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Fig. 2—Installation of Q674 Subbase on wall.  
Fig. 3—Subbase components and leveling  
procedure.  
TOP MOUNTING HOLES (2)  
WALL  
WIRING  
TERMINAL  
WIRES THROUGH  
WALL OPENING  
THERMOSTAT  
SPIRIT LEVEL  
CABLE OPENING  
WALL  
ANCHORS  
(2)  
MOUNTING  
HOLES  
SUBBASE  
MOUNTING HOLES (2)  
TO SPRING FINGER CONTACTS  
ON THE THERMOSTAT  
UP TO 12)  
POST (2) FOR  
MOUNTING  
THERMOSTAT  
MOUNTING  
SCREWS (2)  
M926  
(
M927  
IMPORTANT: Use 18 gauge, color-coded thermostat  
Fig. 4—Wiring Connections.  
cable for proper wiring.  
FOR STRAIGHT  
INSERTION–  
FOR WRAPAROUND–  
STRIP 7/16 in. [11 mm]  
3
. Pull wires through the cover plate (if used) and  
STRIP 5/16 in. [8 mm]  
sub-base cable opening. See Fig. 3. Take care that wires  
do not fall back into the wall opening.  
4
. Secure the cover plate (if used) and subbase with the  
screws provided. Do not fully tighten the subbase screws.  
. Level the subbase using a spirit level, as shown in  
BARRIER  
5
SUBBASE TERMINAL SCREW  
M928  
Fig. 3, and firmly tighten subbase mounting screws.  
The subbase mounting holes provide for minor out-of-  
level adjustments.  
1. Connect the system wires to the subbase as shown  
in Figs. 5-11. A letter code located near each terminal is  
for identification. The terminal barrier permits straight or  
conventional wraparound wiring connection. See Fig. 4.  
IMPORTANT: An incorrectly leveled subbase will cause  
the temperature control to deviate from set point.  
2
. Firmly tighten each terminal screw.  
WIRING THE SUBBASE  
3. Fit wires as close as possible to the subbase. Push  
All wiring must comply with local electrical codes and  
ordinances. Follow equipment manufacturer wiring instruc-  
tions when available. To wire subbase, proceed as follows:  
excess wire back into the hole.  
4. Plug hole with nonflammable insulation to pre-  
vent drafts from affecting the thermostat.  
3
69-0435—10  
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Fig. 5—Internal schematic and typical wiring diagram for Y594G1252 (T874G1246/Q674F1212); auto  
changeover in cooling.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
L1  
(HOT)  
H1 ANTICIPATOR  
R
2
3
RTD1  
OTD1  
FAN  
SWITCH  
L2  
1
EHR1  
ODT2  
EHR2  
RTD2  
AUTO  
ON  
2
H1  
FALL  
W3  
W2  
4
H2  
RTD3  
ANTICIPATOR  
5
6
H2  
FALL  
AUX. HEAT  
LED (GRN)  
SYSTEM  
SWITCH  
RTD1  
OFF  
X
SYSTEM  
8
9
MONITOR  
COOL  
AUTO  
HEAT  
EM. HEAT  
LED (RED)  
FAN  
RELAY  
L
RISE  
G
C1  
ANTICIPATOR  
RD  
COOL  
CHANGEOVER VALVE  
CHANGEOVER  
EM. HT.  
10  
O
E
EM. HEAT  
RELAY  
CHP  
RISE  
C1  
COMPRESSOR  
CONTACTOR  
LACO  
Y
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD  
PROTECTION AS REQUIRED.  
M1589  
W3 TERMINAL ON SELECT MODELS.  
Fig. 6—Internal schematic and typical wiring diagram for T874G1246/Q674F1410. Separate W1 and Y1  
terminals can be jumpered together to form Y terminal.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
W3  
W1  
W1 RELAY  
W3 RELAY  
B RELAY  
H1  
2
FALL  
H1 ANTICIPATOR  
FAN SWITCH  
B
3
FAN RELAY  
AUTO  
ON  
G
R
4
5
L1  
(HOT)  
AUX. HEAT RELAY  
L2  
H2  
6
W2  
1
ANTICIPATOR  
SYSTEM  
SWITCH  
FALL  
AUX. HEAT  
OFF  
LED (GREEN)  
EM. HT.  
H2  
3
X
HEAT  
8
EM. HT.  
LED (RED)  
AUTO  
COOL  
9
CO  
L
COMPRESSOR  
FAULT  
C1 ANTICIPATOR  
RISE  
E
COOL  
CHANGEOVER  
10  
EM. HT.  
RELAY  
VALVE  
RISE  
O
COMPRESSOR  
CONTACTOR  
C1  
2
1
POWER SUPPLY. PROVIDE DISCONNECT  
Y
MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
2
3
ON SOME MODELS, Y TERMINAL MAY BE LABELED Y1.  
M5987A  
EMERGENCY HEAT RUNS CONTINUOUSLY WHEN SWITCH IN IN EM. HT. POSITION.  
6
9-0435—10  
4
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Fig. 7—Internal schematic and typical wiring diagram for Y594G1419 (T874G1642/Q674F1444),  
Y594G1476 (T874G1741/Q674F1477) and Y594G1534 (T874G1824/Q674F1477 sold only in Australia); auto  
changeover in heating and cooling; fixed anticipation. CHECK LED has isolated terminals. Factory-  
installed W1-Y1 jumper is equivalent to Y terminal.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
1
1
2
FAN  
SWITCH  
W3 RELAY  
L1  
L2  
CHANGEOVER  
(HOT)  
W3  
G
(HEAT)  
FAN RELAY  
AUTO  
ON  
FALL  
FALL  
H1  
ANTICIPATOR  
3
R
4
5
AUX. HEAT  
RELAY  
W2  
H2  
EM. HT.  
RELAY  
H2 ANTICIPATOR  
E
AUX.  
HT. LED  
COMPRESSOR  
FAULT  
H1  
FALL  
(GREEN)  
6
SYSTEM  
SWITCH  
X1  
CHECK  
LED (RED)  
CHANGEOVER  
COOL)  
8
9
OFF  
(
EM. HT.  
HEAT  
X2  
EM. HT.  
RISE  
LED (RED)  
AUTO  
COOL  
1
0
X
C1  
ANTICIPATOR  
COOL CHANGEOVER  
RELAY  
O
B
C1  
RISE  
11  
HEAT CHANGEOVER  
RELAY  
W1 RELAY  
W1  
2
COMPRESSOR  
CONTACTOR  
Y1  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
W1 - Y1 JUMPER IS Y TERMINAL; REMOVE JUMPER WHEN W1 RELAY IS USED.  
2
M1230A  
5
69-0435—10  
href="
Fig. 8—Internal schematic and typical wiring diagram for Y594G1526 (T874G1626/Q674F1436); auto  
changeover in heating.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
HOT) L1 L2  
(
1
R
ODT 1  
EHR 1  
ODT 2  
H1 ANTICIPATOR  
FALL  
2
RTD 1  
RTD 2  
H1  
FAN SWITCH  
3
4
AUTO  
ON  
H2  
ANTICIPATOR  
EHR 2  
RTD 3  
RTD 1  
5
W2  
H2  
FALL  
AUX. HEAT  
LED (GREEN)  
X
SYSTEM  
SWITCH  
EM. HT.  
COMPRESSOR  
FAILURE  
LED (RED)  
RD  
OFF  
EM. HT.  
HEAT  
L
7
FALL  
CHANGEOVER  
G
B
FAN RELAY  
AUTO  
HEAT  
8
9
CHANGEOVER  
VALVE  
COOL  
EM. HT.  
RELAY  
E
Y
10  
C1  
ANTICIPATOR  
EHT1  
LACO  
CHP  
COMPRESSOR  
CONTACTOR  
C1  
RISE  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
M1592A  
Fig. 9—Internal schematic and typical wiring diagram for T874D1165, T874E1016/Q674F1543. Exact  
replacement for York model no. 2TB04700524.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
L1  
HOT)  
L2  
(
HEAT RELAY 1  
1
W1  
1
FAN  
H1  
SWITCH  
HEAT RELAY 2  
FALL  
AUTO  
W2  
R
H1 ANTICIPATOR  
ON  
4
X
LED  
RED)  
2
(
H2  
H2  
B
6
8
EM. HEAT RELAY  
FALL  
ANTICIPATOR  
E
SYSTEM  
SWITCH  
OFF  
FAN RELAY  
C1  
G
RISE  
EM. HT.  
HEAT  
COMPRESSOR  
CONTACTOR 2  
9
Y2  
Y1  
AUTO  
COOL  
1
0
COMPRESSOR  
CONTACTOR 1  
C1 ANTICIPATOR  
C2 ANTICIPATOR  
1
1
C2  
RISE  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
LED IS NOT LABELED. JUMPER W2 TO X FOR AUXILIARY HEAT INDICATION. JUMPER E TO X FOR  
EMERGENCY HEAT INDICATION. CONNECT SYSTEM MONITOR TO X TO IDENTIFY WHEN SYSTEM  
NEEDS TO BE CHECKED.  
M2982A  
6
9-0435—10  
6
href="
Fig. 10—Internal schematic and typical wiring diagram for Y594G1567 (T874G1865/Q674J1209) and  
Y594G1575 (T874G1873/Q674J1225); auto changeover in cooling. Exact replacement for York model  
nos. 2TH11702424 and 6TH11702424.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
FALL  
O
2
FAN  
COOL CHANGEOVER VALVE  
H1  
SWITCH  
H1 ANTICIPATOR  
H2 ANTICIPATOR  
G
R
AUTO  
3
4
FAN RELAY  
L1  
ON  
(HOT)  
L2  
1
FALL  
5
6
W
H2  
AUX. HEAT RELAY  
SYSTEM  
SWITCH  
RISE  
X
CO  
8
9
EM. HEAT RELAY  
EM. HT.  
AUTO  
OFF  
EM. HEAT  
LED (RED)  
B
COMPRESSOR  
CONTACTOR  
C1 ANTICIPATOR  
1
RISE  
Y
0
C1  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
M5723  
Fig. 11—Internal schematic and typical wiring diagram for Y594G1633 (T874G1972/Q674F1584); auto  
changeover in heating and cooling.  
THERMOSTAT  
SUBBASE  
SYSTEM COMPONENTS  
1
O
G
FALL  
H1  
FAN SWITCH  
H1 ANTICIPATOR  
COOL CHANGEOVER  
VALVE  
AUTO  
ON  
2
B RELAY  
FAN RELAY  
B
R
E
4
6
L1  
(HOT)  
SYSTEM  
SWITCH  
L2  
H2  
1
ANTICIPATOR  
OFF  
EM. HT. RELAY  
H2 FALL  
EM. HT.  
L
HEAT  
EM. HT.  
LED (RED)  
AUTO  
COOL  
X
RISE  
8
9
AUX. HEAT  
LED (GREEN)  
C1  
AUX. HEAT RELAY  
W2  
Y
C1 ANTICIPATOR  
10  
COMPRESSOR  
CONTACTOR  
11  
RISE  
CO  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
M5986  
12  
7
69-0435—10  
href="
MOUNTING THE THERMOSTAT  
. Remove the thermostat cover by pulling the bot-  
tom edge of the cover away from the base until it snaps  
The current draw must be measured with the thermo-  
stat removed and the power on.  
Do not short across primary control terminals. This  
may burn out the heat anticipator.  
1
free of the retaining posts.  
1
. Connect an ac ammeter of appropriate range be-  
NOTE: The cover is hinged at the top and must be  
removed by pulling out at the bottom.  
tween the heating terminals of the subbase as follows:  
•
•
Stage 1: between W1 and RH or R.  
Stage 2: between W2 and RH or R.  
2
. Carefully remove and discard the foam packing in-  
sert that protects the mercury switches during shipment.  
. If thermostat is being used with a Q674 Subbase  
2
. Move the system switch to HEAT or AUTO, and  
set the temperature to call for heat.  
. After one minute, read the ammeter and record  
the reading.  
3
3
that has LED indication, and the thermostat set point  
scale does not have preprinted designations (EM.HT.,  
CHECK, etc.), install the desired preprinted insert  
packed with the subbase. Push both thermostat set  
point levers to the far ends of the thermostat. Use index  
finger to gently pull out the set point scale a fraction of  
an inch. Insert the desired preprinted insert into the  
recessed area behind the set point scale. Make sure  
insert is completely seated in recessed area and reposi-  
tion set point levers to the desired positions.  
4. After mounting the thermostat, set the adjustable  
heat anticipator to match the readings measured in step 3.  
TEMPERATURE SETTING  
Move the heating and the cooling levers to the desired  
positions. The minimum differential between heating and  
cooling set points is 4° or 6° F [2° or 3° C], depending  
on model; the setting levers are designed so they  
cannot be set closer together than 4° or 6° F [2° or 3°  
C], depending on the model.  
4
. 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 elec-  
trical contact with the subbase.  
SUBBASE SETTING  
5
. Set any adjustable heat anticipator indicators to  
the respective current setting of each stage. See Setting  
the Heat Anticipator section.  
6
thermostat base. The tabs fit into the subbase notches.  
Mount the thermostat base on the subbase and tighten  
the captive mounting screws. See Fig. 12.  
CAUTION  
The Q647F1410 will run the EM. HT. relay  
constantly when the system is in the EM. HT.  
position. A cycling stat or limit must be pro-  
vided external to the T874 to control the EM.  
HT. relay.  
!
. Note the tabs along the top inside edge of the  
7
. Place the upper edge of the thermostat cover on  
the thermostat base and swing the cover downward until  
it engages with the retaining posts on the base.  
System switching positions control thermostat op-  
eration as follows:  
OFF: Both the heating and cooling systems are off.  
HEAT: Heating system is controlled by the thermo-  
stat. Cooling system is off.  
Fig. 12—Mounting thermostat on subbase.  
COOL: The cooling system is controlled by the  
thermostat. Heating system is off.  
THERMOSTAT  
EM.HT.: Emergency heat relay is energized. The cool-  
ing system is off. When the heat pump is inoperable,  
switch to EM. HT. setting. The Q674F1410 Subbase  
will run EM. HT. relay continuously until the switch  
position is changed. All other subbases will cycle  
the EM. HT. relay according to room temperature  
via the T874 mercury switch.  
MOUNTING SLOTS (2)  
THERMOSTAT  
MOUNTING POST (2)  
COOL  
50  
60 70 80  
AUTO: Thermostat automatically changes between heat  
and cool modes, depending on the indoor temperature.  
50  
60 70 80  
HEAT  
SUBBASE  
Fan switching positions control fan operation as follows:  
ON: Fan operates continuously.  
AUTO: Fan operates with heating or cooling equip-  
THERMOSTAT  
ment as controlled by the thermostat.  
CAPTIVE MOUNTING  
SCREWS (2)  
M936  
To switch positions, use thumb or index finger to  
slide the lever to the desired position. Switch lever must  
stop in detent over the desired function indicator mark  
for proper circuit operation.  
Setting  
SETTING THE HEAT ANTICIPATOR  
On models with adjustable anticipation, set each ad-  
justable anticipator to match the primary control current  
draw. If the primary control nameplate has no rating or if  
further adjustment is necessary, use the following proce-  
dure to determine the current draw for each stage.  
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Checkout  
Calibration  
HEATING  
THERMOSTAT  
T874 Thermostats are accurately calibrated at the  
factory. They do not have provision for field calibration.  
Move the system switch on the Q674 Subbase to  
HEAT. Move the heating set point lever on the T874  
Thermostat about 10° F [6° C] above room tempera-  
ture. Both stages of heating and fan should start. Move  
the set point lever about 10° F [6° C] below room  
temperature. Heating and fan should shut off.  
THERMOMETER  
1. Remove thermostat cover by pulling the bottom  
edge of the cover away from the base until it snaps free  
from the retaining posts.  
NOTE: To prevent compressor short cycling, a minimum  
off-timer may be included to provide a five-minute time  
delay before turning on the compressor after the thermo-  
stat last turned off the compressor, or after the system  
first received power. This delay protects the compressor.  
2. Set the cover on a table near an accurate thermometer.  
3. After allowing 10 or 15 minutes for stabilization,  
compare the readings. If they are the same, replace the  
cover and put the system into operation. If they are  
different, recalibrate the thermostat thermometer, step 4.  
4
. Insert a small screwdriver in the thermometer shaft  
COOLING  
(
Fig. 13) and turn it until the thermometers read the  
same. When the thermometer is calibrated, replace the  
cover and place the system into operation.  
CAUTION  
!
Do not operate cooling if the outdoor tempera-  
ture is below 50° F [10° C]. Refer to manufac-  
turer recommendations.  
NOTE: Hand heat will offset the thermometer reading.  
After making each adjustment, wait 10 or 15 minutes  
for the thermometer to stabilize before comparing.  
Move the system switch on the Q674 Subbase to  
COOL. Move the cooling set point lever on the T874  
Thermostat about 10° F [6° C] below room tempera-  
ture. Cooling and fan should start (see CAUTION).  
Move the cooling set point lever about 10° F [6° C]  
above room temperature. Cooling and fan should stop.  
Fig. 13—Thermometer calibration.  
EMERGENCY HEAT  
Change the system switch to EM. HT. The EM. HT.  
LED will come on. The Q674F1410 Subbase starts the  
electric strip heater(s) when put in the EM. HT. position  
(
see CAUTION in Subbase Setting section). All other  
subbases will be tested by moving the set point lever  
about 10° F [6° C] above room temperature. The electric  
strip heater(s) will come on. Reset the set point lever  
about 10° F [6° C] below room temperature. The electric  
strip heater will de-energize. The EM. HT. LED remains  
on until the 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, the fan operates  
with the heating or cooling equipment.  
M5070  
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Home and Building Control  
Honeywell  
Home and Building Control  
Honeywell Limited—Honeywell Limitée  
35 Dynamic Drive  
1985 Douglas Drive North  
Golden Valley, Minnesota 55422  
Scarborough, Ontario  
M1V 4Z9  
6
9-0435–10  
Printed in U.S.A.