Honeywell Tradeline T874A-F User manual

160-1227—1S. M. • Rev. 6-93 • • ©Honeywell Inc. 1993 • Form Number 60-1227—1
T874A-F Multistage Thermostats
with Restricted Set Point
Q674A-E,G Subbases
Installation Instructions for the Trained Service Technician.
Application
TheT874A-FThermostatsprovide24to30Vaccontrol
for heating and/or cooling systems. See Tables 1 and 2.
TABLE 1—HEATING AND/OR COOLING STAGES.
T874 A B C D E F
Heating Stages 1122— 2
Cooling Stages 1212 2 —
The Q674A-E,G Subbases provide wiring terminals,
system and fan switching, and mounting bases for T874
Multistage Thermostats.
TABLE 2—SWITCHING POSITIONS.
Q674 Switch Positions
Model System Fan
AHeat-Auto-Cool Auto-On
BHeat-Off-Cool Auto-On
COff-Auto Auto-On
DNone None
EOff-Heat-Auto-Cool Auto-On
GOff-Auto None
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.
There are about 2°F [1°C] between stages so that the
second stage makes only when the first stage can not
handle the load. This is the interstage differential.
The LED indicators are light emitting diodes on the
subbase that light when something specific happens with-
in the system.
Up to four of the LEDs listed below may be included on
your subbase. When an LED lights, refer to the following
list for the meaning:
FILTER: Clogged filter needs replacement.
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.
AUX. HT.: Auxiliary heat is operating, which means the
weather is so cold that the heat pump can not handle
the load alone.
LOCKOUT:Systemisshutdownandneedsmaintenance.
CHECK: System needs to be checked. See heating sys-
tem instructions for specific meaning.
SERVICE: See heating system instructions for specific
meaning.
LEDs are not field replaceable.
M3375
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. Installation
WHEN INSTALLING THIS PRODUCT…
1. Read these instructions carefully. Failure to fol-
low 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.
3. Installer must be a trained, experienced service
technician.
4. After installation is complete, check out the product
operation as provided in these instructions.
M3375

2
!
CAUTION
1. Disconnect the power supply to prevent elec-
trical shock and 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 thermo-
stat operation.
3. Do not tighten the thermostat captive mount-
ing screws to the point of damaging the sub-
base threads.
4. Do not short across coil terminals on the relay.
This may burn out the heat anticipator.
IMPORTANT: Thermostats are calibrated at the factory by
using subbases mounted at true level. Inaccurate sub-
base leveling will cause thermostat control deviation.
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 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 THE SUBBASE
The thermostat subbase can be mounted on a vertical
outlet box, horizontal outlet box or directly on the wall.
1. To mount 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. The horizontal outlet box requires
placing the subbase on the box and tightening two mount-
ing screws.
For a wall installation, hold the subbase in position and
mark the holes for the anchors. See Fig. 2. Obtain wall
anchors locally. Be careful that the wires do not fall back
into the wall opening. Set subbase aside. Drill two 3/16 in.
[5 mm] holes and gently tap anchors into the holes until
flush with the wall.
2. Pull electrical wires through the cover plate (if used)
and subbase cable opening. See Fig. 3. See Wire the Sub-
base section before pulling any wires.
IMPORTANT: Use 18 gauge, color-coded thermostat
cable for proper wiring.
3. Secure the cover plate (if used) and subbase with the
screws provided. Do not fully tighten the subbase screws.
4. Level the subbase using a spirit level, see Fig. 3, and
firmly tighten the subbase mounting screws. The subbase
mounting holes allow for minor out-of-level adjustments.
IMPORTANT:An incorrectlyleveled subbasewill cause
the temperature control to deviate from set point.
Fig. 1—Installation of subbase on outlet box.
M925
VERTICAL 
OUTLET
BOX
ADAPTER
RING
SUBBASE
COVER 
PLATE

MOUNTING
SCREWS (2)
MOUNTING
SCREWS (2)
1
SUBBASE
MOUNTING
SCREWS (2)
HORIZONTAL
OUTLET
BOX 1
2
2

NOT INCLUDED WITH UNIT.

ACCESSORY PARTS AVAILABLE (193121A).
1
2

Fig. 2—Installation of subbase on wall.
WIRES THROUGH
WALL OPENING
WALL
WALL
ANCHORS
(2)
SUBBASE MOUNTING
SCREWS (2)
M926
MOUNTING
HOLES
Fig. 3—Subbase components and leveling
procedure.
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

360-1227—1
WIRE THE SUBBASE
Disconnect power supply before beginning installation
to prevent electrical shock or equipment damage. All wiring
must comply with local electrical codes and ordinances.
Follow equipment manufacturer’s wiring instructions when
available. To wire the subbase, proceed as follows:
1. Connect the system wires to the subbase. See Figs. 5
through 11. A letter code is located near each terminal for
identification. The terminal barrier permits straight or con-
ventional wraparound wiring connections. See Fig. 4.
2. Firmly tighten each terminal screw.
3. Fit wires as close as possible to the subbase. Push
excess wire back into the hole.
4. Plug the hole with nonflammable insulation to pre-
vent drafts from affecting the thermostat.
Fig. 4—Wiring connections.
M932A
1
2
3
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
JUMPER RC, RH FOR SINGLE TRANSFORMER.
OPTIONAL CHECK-LITE ON SOME MODELS.
COMPRESSOR
CONTACTOR 1
H2 ANTICIPATOR
C1
C1
ANTICIPATOR
C2
H1 ANTICIPATOR
H1
HEAT RELAY 1
HEAT RELAY 2
COMPRESSOR
CONTACTOR 2
FAN RELAY
FALL L1
(HOT)
1
L2
RH
W1
W2
G
Y2
Y1
L1
(HOT)
1
L2
RC
FALL
H2
RISE
C2 ANTICIPATOR
RISE
HEAT
COOL
SYSTEM
SWITCH
AUTO
AUTO
ON
FAN
SWITCH
2
CHECK
3
X1
Fig. 5—T874D/Q674A in standard heating/cooling system.
FOR STRAIGHT
INSERTION–
STRIP 5/16 in. [8 mm] FOR WRAPAROUND–
STRIP 7/16 in. [11 mm]
SUBBASE TERMINAL SCREW
M928
BARRIER

4
Fig. 6—T874D/Q674B in standard heating/cooling system.
M5122
1
2
3
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
JUMPER TERMINALS RC-RH FOR SINGLE SYSTEM TRANSFORMER ONLY.
B,O TERMINALS ON SOME MODELS.
COMPRESSOR
CONTACTOR 1
C1
C1
ANTICIPATOR
C2
COMPRESSOR
CONTACTOR 2
COOL DAMPER
FAN RELAY
O
G
Y2
Y1
L1
(HOT)
1
L2
RC
RISE
C2 ANTICIPATOR
RISE
AUTO
SYSTEM
SWITCH
OFF
H2 ANTICIPATOR
H1 ANTICIPATOR
H1
HEAT DAMPER
HEAT RELAY 1
HEAT RELAY 2
FALL L1
(HOT)
1
L2
RH
W1
W2
B
FALL
H2
AUTO
ON
FAN
SWITCH
3
2
2
Fig. 7—T874D/Q674C in standard heating/cooling system.
M933A
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
JUMPER RC AND RH FOR SINGLE TRANSFORMER SYSTEMS.
OPTIONAL LIGHT ON SOME MODELS.
COMPRESSOR
CONTACTOR 1
H2 ANTICIPATOR
C1
C1
ANTICIPATOR
C2
H1 ANTICIPATOR
H1
HEAT DAMPER OR
CHANGEOVER RELAY
HEAT RELAY 1
HEAT RELAY 2
COMPRESSOR
CONTACTOR 2
COOL DAMPER OR
CHANGEOVER RELAY
FAN RELAY
FALL
L1 (HOT)
1
L2
RH
W1
W2
B
O
G
Y2
Y1 L1
(HOT)
1
L2
RC
FALL
H2
RISE
C2 ANTICIPATOR
RISE
HEAT
COOL
SYSTEM
SWITCH
OFF
AUTO
ON
FAN
SWITCH
2X1
3
3

560-1227—1
Fig. 8—T874D/Q674D in standard heating/cooling system.
M3667
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

JUMPER RC, RH FOR SINGLE TRANSFORMER.

B TERMINAL OPTIONAL.
COMPRESSOR
CONTACTOR 1
H2 ANTICIPATOR
C1
C1 ANTICIPATOR
C2
H1 ANTICIPATOR
H1 HEAT RELAY 1
HEAT RELAY 2
COMPRESSOR
CONTACTOR 2
FALL
L1
(HOT)
L2
RH
W2
Y2
Y1
L1
(HOT)
L2
RC
FALL H2
RISE
C2 ANTICIPATOR
RISE
NO
FAN
SWITCH
NO
SYSTEM
SWITCH
W1
B1
1
3
2
3
2
Fig. 9—T874D/Q674E in standard heating/cooling system.
M934
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
JUMPER RC, RH FOR SINGLE TRANSFORMER.
COMPRESSOR
CONTACTOR 1
H2 ANTICIPATOR
C1
C1
ANTICIPATOR
C2
H1 ANTICIPATOR
H1
HEAT RELAY 1
HEAT RELAY 2
COMPRESSOR
CONTACTOR 2
FAN RELAY
FALL L1
(HOT)
1
L2
RH
W1
W2
B
G
Y2
Y1
L1
(HOT)
1
L2
RC
FALL
H2
RISE
C2 ANTICIPATOR
RISE
HEAT
COOL
SYSTEM
SWITCH
AUTO
AUTO
ON
FAN
SWITCH
2
OFF
O

6
Fig. 10—T874D/Q674G in standard heating/cooling system.
M3726
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

JUMPER RC, RH FOR SINGLE TRANSFORMER.
C1
C1 
ANTICIPATOR
H2 
ANTICIPATOR
H1
HEAT RELAY 2
COMPRESSOR
CONTACTOR 1
FALL L1
(HOT)
L2
B
W2
Y1
RC
RISE
W1 1
1
2
2
SYSTEM SWITCH
OFF
AUTO
RH
O
Y2
L1
(HOT)
L2
1
HEAT RELAY 1
H2
FALL
RISE
C2
COMPRESSOR
CONTACTOR 2
H1 ANTICIPATOR NO FAN
SWITCH
C2 
ANTICIPATOR
Fig. 11—Typical Q674 terminal designations. The thermostat used determines the number of connections.
STAGE 1
HEATING
RELAY
HEATING DAMPER
MOTOR (OR
CHANGEOVER
VALVE)
STAGE 2
HEATING
RELAY
STAGE 3
HEATING
RELAY
CLOGGED
FILTER
SWITCH
SYSTEM
MONITOR
OUTDOOR
THERMISTOR
EMERGENCY
HEAT
RELAY
LED
STAGE 1
COOLING
RELAY
STAGE 2
COOLING
RELAY
COOLING
FAN RELAY
COIL
COOLING DAMPER
MOTOR (OR
CHANGEOVER
VALVE)
RC OW3 L
X
Y1 Y2
W1
X1
RH W2
ETGB
Q674
SUBBASE
1 ADD JUMPER (RH-RC) FOR HOOKUP USING COMMON TRANSFORMER.

2 PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
POWER
SUPPLY
2

1
POWER
SUPPLY 2
M954

760-1227—1
Fig. 12—Restricted set point.
MOUNTING THE THERMOSTAT
1. Remove the thermostat cover by pulling the bottom
edge of the cover upward until it snaps free of the cover clip.
NOTE: The cover is hinged at the top. Remove it by pull-
ing up at the bottom.
2. Carefullyremove and discard thepolystyrenepacking
insert,whichprotectsthemercury switchesduringshipment.
3. Turn the thermostat base over 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.
4. Set the heat anticipator indicators to the respective
current setting for each stage. See Setting the Heat Antici-
pator section.
5. Notethe tabs along the top insideedgeof the thermo-
stat base. The tabs fit into the subbase notches. Mount the
thermostat base on the subbase and tighten the captive
mounting screws. See Fig. 1.
6. Place the upper edge of thermostat cover on the
thermostatbaseandswingcoverdownward untilit engages
with the cover clip on the base.
Setting
SETTING THE HEAT ANTICIPATOR
Set each heat anticipator to match its primary control
currentdraw. If the primarycontrolnameplate has no rating
or if further adjustment is necessary, use the following
procedure to determine the current draw of each stage. The
current draw of each heating stage must be measured with
the thermostat removed and the power on.
1. Connectanac ammeter of appropriate range between
the heating terminals of the subbase:
Stage 1: between W1 and RH or R.
Stage 2: between W2 and RH or R.
2. Move the system switch to HEAT or AUTO.
3. After one minute, read the ammeter and record the
reading.
4. Aftermounting thethermostat,set theadjustableheat
anticipator(s) to match the respective reading(s) measured
in step 3.
TEMPERATURE SETTING
Move the heating and cooling levers to the desired
positions. The minimum differential between the heating
and cooling set points is 3°F [2°C], which means the
setting levers cannot be set closer together than 3°F [2°C].
The T874 is equipped with a restricted set point feature
for fuel efficiency.
Factory-installed stops are set so the set point levers
cannot be set above 68°F [20°C] or 72°F [22°C] on
heating(depending onthe model)orbelow78°F[26°C] on
cooling (Fig. 12).
Do not attempt to change the location of these stops,
because they are nonadjustable.
SUBBASE SETTING
System switching positions control thermostat opera-
tion as follows:
OFF:Boththeheatingandcoolingsystemsareoff.Ifthe
fanswitchis in the AUTO position, the cooling fan is
also off (Q674B,C,E or G only).
HEAT: Heating system is controlled by the thermostat.
Cooling system is off (Q674A,B or E only).
COOL: Thermostat controls the cooling system. Heat-
ing system is off (Q674A, B or E only).
AUTO:Thethermostatautomaticallyswitchesbetween
heat and cool modes, depending on the indoor tem-
perature (Q674A,C,E or G only).
Fan switching positions control fan operation as fol-
lows (Q674A,B,C or E):
ON: Fan operates continuously.
AUTO: Fan operates with cooling equipment as con-
trolled by the thermostat or with the heating equip-
ment as controlled by the plenum switch.
To switch positions, use thumb and index finger to slide
lever to the desired position. The switch lever must stop
over the desired function indicator mark for proper circuit
operation.
Checkout
HEATING
Move the system switch on the Q674 Subbase to HEAT
or AUTO. Move the heating lever on the T874 about 10°F
[6°C] above room temperature. Both stages of heating
should start and the fan should run after a short delay.
Move the heating lever about 10°F [6°C] below room
temperature. The heating equipment should shut off, and
the fan should run for a short time and then shut off.
COOLING
Move the system switch on the Q674 Subbase to COOL
or AUTO. Move the cooling lever on the T874 Thermostat
about 10°F [6°C] below room temperature. The cooling
equipment and fan should start. Move the cooling lever
about 10°F [6°C] above room temperature. The cooling
equipment and fan should stop.
FAN
Move the subbase system switch to OFF or AUTO, and
the fan switch to ON. The fan should run continuously.
When the fan switch is in the AUTO position, the fan
operation is controlled by the heating or cooling system.

8
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Honeywell Inc. Honeywell Limited—Honeywell Limitée
1985 Douglas Drive North 740 Ellesmere Road
Golden Valley, MN 55422 Scarborough, Ontario
M1P 2V9
Printed in U.S.A. www.honeywell.com/yourhome
QUALITY IS KEY
Calibration
THERMOSTAT
T874 Thermostats are accurately calibrated at the fac-
tory. They do not have provision for field calibration.
THERMOMETER
1. Remove thermostat cover by pulling up from the
bottom of cover until it clears the locking springs.
2. Set the cover on a table near an accurate thermometer.
3. After allowing five or ten minutes for stabilization,
compare the readings. If they are the same, replace the
cover and put the system into operation. If they are differ-
ent, recalibrate the thermostat thermometer; see step 4.
4. Insert a small screwdriver in the thermometer shaft
(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.
NOTE: Hand heat will offset the thermometer reading.
After making each adjustment, wait five or ten minutes
for the thermometer to stabilize before comparing.
Fig. 13—Thermometer calibration.
M5070