Honeywell TROL-A-TEMP T874A User manual

X-XX UL
INSTALLATION INSTRUCTIONS
®U.S. Registered Trademark
Copyright © 1996 Honeywell Inc. • All Rights Reserved
T874A,D,R Thermostats and
Q674B,D,F,Q Subbases
APPLICATION
These thermostat/subbase combinations provide low voltage (24 Vac) control in multistage systems as follows:
Thermostat/
Number of
Stages Switching Positions Wiring
Subbase Heat Cool System Fan Fig.
T874A/Q674Q 1 1 HEAT-OFF-COOL LO-MED-HIGH-ON 4
T874D/Q674F 2 2 AUX HT-HEAT PUMP-2 STG. HEAT-OFF-COOL AUTO-ON 5
T874R/Q674B 2 1 HEAT-OFF-COOL AUTO-ON 6,7
T874D/Q674D 2 2 None None 8
T874D/Q674B 2 2 HEAT-OFF-COOL AUTO-ON 9
OPERATION
On a two-stage 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.
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 called 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 this list
for the meaning:
AUX. HEAT: Auxiliary heat is operating, which means
the weather is so cold that the heat pump alone
cannot handle the load.
HEAT PUMP: System needs to be checked. See
heating system instructions for specific meaning.
LEDs are not field replaceable.
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.
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.
INSTALLATION
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.
4. After installation is complete, check out product
operation as provided in these instructions.
69-0107-2

69-0107—2 2
T874A,D,R THERMOSTATS AND Q674B,D,F,Q SUBBASES
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.
3. Do not overtighten the thermostat captive
mounting screws because damage to the
subbase threads can result.
4. Do not short across coil terminals on the relay.
This can burn out the heat indicator.
IMPORTANT
An incorrectly leveled thermostat can cause the
temperature control to deviate from setpoint. It is
not a calibration problem.
Location
Install the thermostat about 5 ft (1.5m) above the floor in a
well-circulated area of average 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.
Mount Subbase
The subbase can be mounted on a vertical or horizontal
outlet box (see Fig. 1) or directly on the wall (see Fig. 2).
To mount the subbase on a vertical outlet box, order
193121A Adapter Assembly, which includes an adapter
ring, two screws and a cover plate to cover marks on
the wall.
IMPORTANT
An incorrectly leveled subbase can cause the
temperature control to deviate from setpoint.
To mount the subbase on the wall:
쐃Hold the subbase in position and mark the holes for
the anchors. Wall anchors must be obtained locally.
Make sure that the wires do not fall back into the
wall opening.
쐇Set aside the subbase.
쐋Drill four 3/16 in. (4.6 mm) holes and gently tap the
anchors into the holes until flush with the wall.
쐏Pull electrical wires through the cover plate, if used,
and through the subbase wire opening. See Fig. 2.
Secure the cover plate and subbase with the two
screws provided, but do not fully tighten the screws.
쐄The subbase mounting slots allow minor out-of-level
adjustments. Level the subbase using a spirit level,
as shown in Fig. 3, and tighten the subbase
mounting screws.
M6009
VERTICAL
OUTLET
BOX
ADAPTER
RING
COVER
PLATE
MOUNTING
SCREWS (2)
1
SUBBASE
SUBBASE
MOUNTING SCREWS (2)
HORIZONTAL
OUTLET
BOX
1
2
2
1 NOT INCLUDED WITH UNIT.
2 ACCESSORY PART AVAILABLE (193121A).
THERMOSTAT
CAPTIVE
MOUNTING SCREWS (2)
50 60 70 80
50 60 70 80
HEAT COOL
THERMOSTAT
COVER
50607080
Fig. 1. Installation of Q674 Subbase on outlet box.
WIRES THROUGH
WALL OPENING
WALL
WALL
ANCHORS
(2)
SUBBASE
MOUNTING
SCREWS (2)
M926
MOUNTING
HOLES
Fig. 2. Installation of Q674 Subbase on wall.

69-0107—2
3
T874A,D,R THERMOSTATS AND Q674B,D,F,Q SUBBASES
Fig. 3. Level the subbase.
SPIRIT LEVEL
MOUNTING
HOLES (2)
M927
TOP
MOUNTING
HOLES (2)
WIRING
TERMINAL
THERMOSTAT
CABLE OPENING
TO SPRING FINGER
CONTACTS ON THE
THERMOSTAT
(UP TO 12)
POST (2) FOR
MOUNTING
THERMOSTAT
Wire Subbase
IMPORTANT
Use 18-gauge, color-coded thermostat wire for
wiring the Q674 Subbase.
Disconnect power supply to prevent electrical shock or
equipment damage. All wiring must comply with local
electrical codes and ordinances. Follow equipment
manufacturer wiring instructions when available.
쐃Connect the system wires to the subbase as
shown in Fig. 4 through 9. A letter code is located
near each terminal for identification. The terminal
barrier allows straight or conventional wraparound
wiring connections. Either method is acceptable.
See Fig. 10.
쐇Run wires as close as possible to the subbase,
keeping wire length to a minimum.
쐋Push excess wire back into the hole.
쐏Plug the hole to prevent drafts.
H1
FALL
L1
(HOT)
L2
1
C1 RISE
M8005
2
1
2
H1
ANTICIPATOR
C1
ANTICIPATOR
5
4
2
1W1
B
R
G1
G2
O
Y1 HI
MED
LO
K2
K1
K2 K2
K1
COMPRESSOR CONTACTOR
O RELAY
K2 RELAY
K1 RELAY
B RELAY
HEAT RELAY 1
SYSTEM
SWITCHHEAT
OFF
COOL
FAN
SWITCH
LO
MED
HIGH
ON
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
SINGLE SETPOINT LEVER AND BIMETAL.
3
L2 L1
THERMOSTAT SUBBASE SYSTEM COMPONENT
3-SPEED FAN SCHEMATIC
Fig. 4. Internal schematic and typical hookup of T874A Thermostat with
Q674Q Subbase with automatic changeover.

69-0107—2 4
T874A,D,R THERMOSTATS AND Q674B,D,F,Q SUBBASES
Fig. 5. Internal schematic and typical hookup of T874D Thermostat with Q674F Subbase with manual changeover.
Fig. 6. Internal schematic and typical hookup of T874R Thermostat with
Q674B Subbase in heat pump system with changeover in cooling.
H1 FALL
H2 FALL
C1 RISE
C2 RISE
L1
(HOT)
L2 1
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
THERMOSTAT SUBBASE SYSTEM COMPONENTS
H1 ANTICIPATOR
H2 ANTICIPATOR
C1 ANTICIPATOR
C2 ANTICIPATOR
SYSTEM
SWITCH
FAN
SWITCH
AUTO
ON
OFF
2 STG. HEAT
HEAT PUMP
AUX. HT.
COOL
FAN RELAY
AUX. HT. RELAY
COOL CHANGEOVER
VALVE
COMPRESSOR
CONTACTOR 1
COMPRESSOR
RELAY
COMPRESSOR
CONTACTOR 2
M4730
HEAT PUMP
LED (GREEN)
AUX. HT
LED (RED)
1
2
4
6
8
10
11 Y2
Y1
C
W2
W1
B
R
G
O
L1
(HOT)
L2 1
COOL
HEAT
FALL
O
G
R
W1
Y
H1/C1
ANTICIPATOR
H2
SYSTEM
SWITCH
FAN RELAY
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
M2906
OFF
COOL CHANGEOVER
VALVE
H1
FALL
C1
FAN
SWITCH
AUTO
ON
THERMOSTAT SUBBASE SYSTEM COMPONENTS
1
2
3
4
5
6
AUX. HT.
RELAY
COMPRESSOR
CONTACTOR

69-0107—2
5
T874A,D,R THERMOSTATS AND Q674B,D,F,Q SUBBASES
Fig. 7. Internal schematic and typical hookup of T874R Thermostat with
Q674B Subbase in heat pump system with changeover in heating.
Fig. 8. Internal schematic and typical hookup of T874D Thermostat with
Q674D Subbase with automatic changeover.
M5998
H2
FALL
H1
FALL
C1
L1
(HOT)
L2 1
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
THERMOSTAT SUBBASE SYSTEM COMPONENTS
H1/C1 ANTICIPATOR
FAN SWITCH
AUTO
ON
SYSTEM
SWITCH
HEAT
OFF
COOL COMPRESSOR
CONTACTOR
AUX. HT. RELAY
HEAT CHANGEOVER
VALVE
FAN RELAY
6
5
4
3
2
1X
G
R
B
W2
Y
H1
FALL
W1
W2
HEAT RELAY 1
H1 ANTICIPATOR
C1 ANTICIPATOR 1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
RC-RH REMOVABLE JUMPER WHEN SPECIFIED.
M2986
THERMOSTAT SUBBASE SYSTEM COMPONENTS
COMPRESSOR
CONTACTOR 2
COMPRESSOR
CONTACTOR 1
1
5
6
8
9
10
11
H2
FALL
C2 ANTICIPATOR
RISE
RISE
C1
C2
Y1
Y2
HEAT RELAY 2
L1
(HOT)
L2
1
H2
ANTICIPATOR
L1
(HOT)
L2
1
RC
RH
2
4
NO
FAN
SWITCH
NO
SYSTEM
SWITCH
2

69-0107—2 6
T874A,D,R THERMOSTATS AND Q674B,D,F,Q SUBBASES
Fig. 9. Internal schematic and typical hookup of T874D Thermostat with Q674B Subbase in heat pump system
with changeover in heating and cooling.
H1
FALL
L1
(HOT)
L2
1
RH
W1
W2
O
G
Y2
Y1
RC
HEAT RELAY 2
HEAT RELAY 1
HEAT
OFF
COOL
SYSTEM
SWITCH
H1 ANTICIPATOR
C1 ANTICIPATOR
AUTO
ON
FAN
SWITCH
2
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
JUMPER RH, RC FOR SINGLE TRANSFORMER.
2
M933C
B
HEAT CHANGEOVER
VALVE
L1
(HOT)
L2
1
COOL CHANGEOVER
VALVE
FAN RELAY
COMPRESSOR
CONTACTOR 2
COMPRESSOR
CONTACTOR 1
1
4
6
8
9
10
11
H2
FALL
C2 ANTICIPATOR
RISE
RISE
C1
C2
X1
3OPTIONAL LED ON SOME MODELS.
THERMOSTAT SUBBASE SYSTEM COMPONENTS
3
H2 ANTICIPATOR
Fig. 10. Wiring connections.
Mounting the Thermostat
쐃Remove the thermostat cover by pulling the bottom
edge of the cover upward until it snaps free from the
cover clip.
NOTE: The cover is hinged at the top and can be
removed by pulling up at the bottom.
쐇Carefully remove and discard the polystyrene
packing insert that protects the mercury switches
during shipment.
NOTE: If the thermostat is being used with a Q674
Subbase with LEDs and the thermostat
setpoint scale is not labeled (such as EM.
HT., CHECK), install the desired LED label
insert (packed with the subbase):
-Push both thermostat setpoint levers to
the far ends of the thermostat.
-Gently pull the setpoint scale out about
1/4 in. (6 mm).
-Insert the desired LED label.
-Reposition the setpoint levers.
FOR STRAIGHT
INSERTION–
STRIP 5/16 IN. (8 MM)
FOR WRAPAROUND–
STRIP 7/16 IN. (11 MM)
SUBBASE TERMINAL SCREW
M928
BARRIER
쐋Turn over the thermostat base and note the spring
fingers that engage the subbase contacts. Make
sure the spring fingers are
not bent flat, which
prevents proper electrical contact with the subbase.
쐏Set the heat anticipator indicators at the respective
current setting for each stage. See Setting the Heat
Anticipator section.
쐄Mount the thermostat base on the subbase noting
the tabs along the top inside edge of the thermostat
base. The tabs fit into the subbase notches.
쐂Tighten the captive mounting screws. See Fig. 1.
쐆Place the upper edge of the thermostat cover on the
thermostat base and swing the cover downward until
it engages with the cover clip on the base.
SETTINGS
Setting the Heat Anticipator
Set the heat anticipator to match the current draw of the
primary control. If the primary control nameplate is not
labeled with a rating, or if further adjustment is necessary,
use the following procedure to determine the current draw
for each stage. Measure the current draw of each heating
stage with the thermostat removed from the subbase and
the power on:
쐃Connect an ac ammeter of appropriate range
between the heating terminals of the subbase:
Stage 1: between W1 and R.
Stage 2: between W2 and R.
쐇Move the system switch to HEAT or AUTO.
쐋After one minute, read the ammeter and record the
reading.

69-0107—2
7
T874A,D,R THERMOSTATS AND Q674B,D,F,Q SUBBASES
쐏After mounting the thermostat, set the adjustable
heat anticipator(s) to match the respective
reading(s) recorded in step 쐋. See Fig. 11.
1.2
.4
.6
.3
.2 .15
.12
.10
.8
1.2
.4
.6
.3
.2 .15
.12
.8
.5
MOVE INDICATOR TO
MATCH CURRENT RATING
OF PRIMARY CONTROL
STAGE ONE
ANTICIPATOR
HEATING
CONTROL
STAGE TWO
ANTICIPATOR
HEATING CONTROL
M5069
Fig. 11. Adjustable heat anticipator scales.
Temperature Setting
쐃Move the heating and cooling levers to the desired
positions. The minimum differential between the
heating and the cooling setpoints is 3°F (2°C), which
means the setting levers are designed so they
cannot be set closer together than 3°F (2°C).
NOTE: If adjustable lever stops are desired, order
4074ECK Bag Assembly, which contains a
brass insert, mounting screw, and two
adjustable stops.
쐇Gently push the brass insert into the backside of the
T874 in the hole below the LED space.
쐋Place the two stops on the face of the T874 in the
space below the LED.
쐏Insert the mounting screw through the two stops,
and into the threaded hole of the brass insert. The
mounting screw pulls the brass insert up through the
back of the plastic base.
쐄Loosen the screw so the stops can slide into the
desired position against the levers.
쐂Tighten the screw. See Fig. 12.
Fig. 12. Installing adjustable lever stops.
Subbase Setting
System switch settings control thermostat operation as
follows:
OFF: Heating and cooling systems are off. If the fan
switch is in the AUTO position, the cooling fan is
also off.
HEAT: Heating system is controlled by the thermostat.
Cooling system is off.
COOL: Thermostat controls the cooling system.
Heating system is off.
AUX. HEAT: Auxiliary heat is on. Cooling system is off.
HEAT PUMP: Both first and second stage heat are on.
Cooling system is off.
2 STG. HEAT: Second stage heat is on. Cooling
system is off.
M7346
HEAT
LEVER
HOLES FOR INSULATED
LOCKING LEVER SCREWS
COOL
LEVER HOLE WITH
BRASS INSERT
BRACKET
TABS
ADJUSTABLE
LEVER STOP
BRACKETS BRACKET
SLOTS
MOUNTING
SCREW

69-0107—2 8
T874A,D,R THERMOSTATS AND Q674B,D,F,Q SUBBASES
Home and Building Control
Honeywell Limited-Honeywell Limitée
155 Gordon Baker Road
North York, Ontario
M2H 2C9
Helping You Control Your World®
69-0107—2 J.S. Rev. 10-96 Printed in U.S.A
Home and Building Control
Honeywell Inc.
Honeywell Plaza
P.O. Box 524
Minneapolis, MN 55408-0524
Fan switch settings control fan operation as follows:
ON: Fan operates continuously.
AUTO: Fan operates with cooling equipment as
controlled by the thermostat or with the heating
equipment as controlled by the plenum switch.
LO: Fan operates at a low speed when heating or
cooling equipment cycles on.
MED: Fan operates at a medium speed when heating
or cooling equipment cycles on.
HIGH: Fan operates at a high speed when heating or
cooling equipment cycles on.
To switch settings, slide the lever to the desired position.
For proper circuit operation, set the switch lever in the
indent directly over the desired switch setting.
CHECKOUT
Heating
쐃Move the system switch on the Q674 Subbase to
HEAT or AUTO, and the fan switch to AUTO (if
applicable).
쐇Move the heating lever on the T874 about 10°F
(6°C) above the room temperature. Both stages of
heating and fan should start if there is no time delay
or outdoor temperature limiting system.
쐋Move the heating lever about 10°F (6°C) below the
room temperature. The heating equipment and fan
should shut off.
Cooling
CAUTION
Do not operate the cooling equipment if the
outdoor temperature is below 50°F (10°C).
Damage to the compressor can result.
쐃Move the system switch on the Q674 Subbase to
COOL or AUTO.
쐇Move the cooling lever on the T874 Thermostat
about 10°F (6°C) below the room temperature. The
cooling equipment and fan should start.
쐋Move the cooling lever about 10°F (6°C) above the
room temperature. The cooling equipment and fan
should stop.
Fan
쐃Move the subbase system switch to OFF or AUTO.
쐇Move 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.
CALIBRATION
Thermostat
T874 Thermostats are accurately calibrated at the factory.
They do not have provision for field calibration .
THERMOMETER
쐃Remove the thermostat cover by pulling up from the
bottom of the cover until it clears the cover clip.
쐇Set the cover on a table near an accurate thermometer.
쐋After allowing five or ten minutes for stabilization,
compare the readings. If the readings are the same,
replace the cover and put the system into operation.
If the readings vary, recalibrate the thermostat
thermometer; see step 쐏.
쐏Insert a small screwdriver in the thermometer shaft
and turn it until the thermometers read the same.
See Fig. 13. When the thermometer is calibrated,
replace the cover and place the system into
operation.
NOTE: Hand heat offsets the thermometer
reading. After making each adjustment,
wait five or ten minutes for the thermometer
to stabilize before comparing the readings.
Fig. 13. Thermometer calibration.
M5070
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