Honeywell T874/Q674 User manual
- Category
- Thermostats
- Type
- User manual
This manual is also suitable for
Honeywell Thermostat T874/Q674 offers precise temperature control for heat pump systems. With its two-stage heating and one-stage cooling operation, it ensures efficient and comfortable temperature management. Advanced features include LED indicators for system status, automatic changeover between heating and cooling modes, and adjustable fan settings for optimal airflow. The thermostat's intuitive interface allows for easy programming and operation, making it a reliable choice for maintaining a comfortable indoor environment.
Honeywell Thermostat T874/Q674 offers precise temperature control for heat pump systems. With its two-stage heating and one-stage cooling operation, it ensures efficient and comfortable temperature management. Advanced features include LED indicators for system status, automatic changeover between heating and cooling modes, and adjustable fan settings for optimal airflow. The thermostat's intuitive interface allows for easy programming and operation, making it a reliable choice for maintaining a comfortable indoor environment.
S. M. • Rev. 5-93 • • ©Honeywell Inc. 1993 • Form Number 60-1147—4
T874/Q674
Thermostat/Subbase Combinations
Installation Instructions for the Trained Service Technician.
Application
The T874/Q674 Thermostat/Subbase combinations provide 24 to 30 Vac control for heat pump systems. See Table 1.
TABLE 1—T874/Q674 THERMOSTAT/SUBBASE COMBINATIONS.
Thermostat/ Number Changeover
Subbase
a
of Stages Stage Type of Switching
Model Heating Cooling Heating Cooling System Fan See Fig.
T874N/Q674C 2 1 1 — OFF-AUTO AUTO-ON 5
T874N/Q674F 2 1 — 1 OFF-EM. HT.- AUTO-ON 6
HEAT-AUTO-COOL
T874R/Q674L 2 1 — 2
b
EM. HT.-HEAT- AUTO-ON 7
OFF-COOL
a
Q674 Subbase provides the wiring terminals, system switch and fan switch for system operation.
b
Provides manual changeover with the subbase system switch in COOL position.
Installation
WHEN INSTALLING THIS PRODUCT…
1. Read these instructions carefully. Failure to follow
them could 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 applica-
tion.
3. Installer must be a trained, experienced service tech-
nician.
4. After installation is complete, check out product opera-
tion as provided in these instructions.
CAUTION
1. Disconnect power supply to prevent electrical
shock and equipment damage.
2. To prevent interference with the thermostat link-
age, keep wire length to a minimum and run
wires as close as possible to the subbase. Push
excess wire back into the hole and plug hole to
prevent drafts from affecting thermostat opera-
tion.
3. Do not overtighten thermostat captive mounting
screws because damage to subbase threads may
result.
4. Do not short across coil terminals on the relay.
This may burn out the thermostat heat
anticipator.
IMPORTANT: Thermostats are calibrated at the factory
using subbases mounted at true level. An inaccurately
leveled subbase will cause thermostat control devia-
tion.
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.
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.
One or two 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 mean-
ing.
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.
The AUX. HT. LED lights when the auxiliary heat stage
is operating. The weather is cold enough that the first stage
cannot handle the load alone.
LEDs are not field replaceable or addable.
M3375
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 in-
structions regarding recycling and the proper disposal of this
control, or of an old control containing mercury in a sealed
tube.
If you have questions, call Honeywell at 1-800-468-1502.
60-1147-4
2
Fig. 1—Installation of Q674 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
1 NOT INCLUDED WITH UNIT.
2 ACCESSORY PARTS AVAILABLE (193121A).
Fig. 2—Installation of Q674 Subbase on wall.
WIRES THROUGH
WALL OPENING
WALL
WALL
ANCHORS
(2)
SUBBASE
MOUNTING
HOLES
MOUNTING
SCREWS (2)
M926
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
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 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.
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 Adapter Assembly (Fig. 1). The as-sembly
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.
For a wall installation, hold subbase in position and mark
holes for anchors (Fig. 2). Obtain wall anchors locally. Take
care that the wires do not fall back into the wall opening. Set
aside subbase. Drill four 3/16 in. [4.8 mm] holes and gently
tap anchors into the holes until flush with the wall.
2. Pull wires through the cover plate (if used) and subbase
cable opening (Fig. 3).
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, as shown in Fig.
3, and firmly tighten the subbase mounting screws. The
subbase mounting holes provide for minor out-of-level ad-
justments.
IMPORTANT: An incorrectly leveled subbase will cause
the temperature control to deviate from set point.
WIRING THE SUBBASE
IMPORTANT: Use 18-gauge color-coded thermostat cable
for proper wiring.
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 wiring instruc-
tions when available. To wire subbase, proceed as follows:
1. Connect the system wires to the subbase as shown in
Figs. 5-7. A letter code located near each terminal is for
identification. The terminal barrier permits straight or con-
ventional wraparound wiring connection (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 hole with nonflammable insulation to prevent
drafts from affecting the thermostat.
MOUNTING THE THERMOSTAT
1. Remove the thermostat cover by pulling the bottom
edge of the cover outward and away from the base until it
snaps free of the mounting slots.
NOTE: The cover is hinged at the top and must be re-moved
by pulling outward at the bottom.
60-1147-43
Fig. 4—Wiring connections.
2. Carefully remove and discard the polystyrene packing
insert that protects the mercury switches during shipment.
3. If LED indication (EM.HT., CHECK, etc.) is to be used
with the Q674 Subbase, install the preprinted insert under the
thermostat set point scale (Fig. 8). To install, push both
thermostat set point levers to the far ends of the thermostat. Use
index finger to gently pull out the plastic set point scale about
1/4 in. [6 mm]. Drop insert into recessed area behind set point
scale so that selected LEDs show. Make sure insert is com-
pletely seated in recessed area. Let set point scale pop back, and
set levers to desired positions.
FOR STRAIGHT
INSERTION–
STRIP 5/16 in. [8 mm]
FOR WRAPAROUND–
STRIP 7/16 in. [11 mm]
SUBBASE TERMINAL SCREW
M928
BARRIER
Fig. 5—Internal schematic and typical wiring diagram for T874N and Q674C.
M1860
G
R
W2
X
L1
(HOT)
L2
AUTO
SYSTEM
SWITCH
AUTO
ON
FAN
SWITCH
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS
REQUIRED.
1
CHECK
LED
(GRN)
L
Y
OFF
H1
ANTICIPATOR
RISE
W3
W1
FAN RELAY
DEFROST RELAY
CONTACT
C1
C1
ANTICIPATOR
FALL
H2
HEAT
RELAY 1
COMPRESSOR
CONTACTOR
EM. HT. RELAY
CONTACT
EM. HT. RELAY
CONTACT
OUTDOOR
THERMOSTAT
HEAT
RELAY 2
HEAT
RELAY 3
REVERSING
RELAY
OPTIONAL
COMPRESSOR
FAILURE
DEVICE
CO
H2 ANTICIPATOR
FALL
H1
60-1147-4
4
Fig. 6—Internal schematic and typical wiring diagram for T874N and Q674F.
L1
HOT
L2
1
W1
W2
EM. HEAT
LED (RED)
CHECK
LED
(GREEN)
FAN RELAY
G
EM. HEAT
RELAY
COMPRESSOR
CONTACTOR
Y
E
SYSTEM
SWITCH
EM. HT.
HEAT
OFF
COOL
H1
ANTICIPATOR
H1
H2
H2
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
M3686
FALL
R
RISE
L
C1
HEAT
RELAY 3
EM.HT. RELAY
CONTACT
OUTDOOR
THERMOSTAT
AUTO
ON
FAN SWITCH
X
W3
OPTIONAL
COMPRESSOR
FAILURE DEVICE
DEFROST
RELAY
REVERSING
VALVE
EM.HT. RELAY
CONTACT
HIGH
PRESSURE
SWITCH
HEAT
RELAY 1
HEAT
RELAY 2
AUTO
FALL
C0
C1
ANTICIPATOR
60-1147-45
Fig. 7—Internal schematic and typical wiring diagram for T874R and Q674L.
L1
HOT
L2
1
X2
W2
EM. HEAT
LED (RED)
AUX. HEAT
LED (GREEN)
HIGH LIMIT
SWITCH
FAN RELAY
G
EM. HEAT
RELAY
COMPRESSOR
CONTACTOR
Y
E
SYSTEM
SWITCH
EM. HT.
HEAT
OFF
COOL
H1/C1
ANTICIPATOR
H1
H2
H2
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
M3685
FALL
R
FALL
L
C1
HEAT
RELAY 1
HEAT
CONTACTOR 3
EM.HT. RELAY
CONTACT
OUTDOOR
THERMOSTAT
HEAT
CONTACTOR 2
AUTO
ON
FAN SWITCH
O
X1
B
W3
OPTIONAL COMP
FAILURE DEVICE
DEFROST
RELAY
DEFROST
RELAY
REVERSING
VALVE
EM.HT. RELAY
CONTACT
COOL RELAY
HIGH
PRESSURE
SWITCH
LOW
AMBIENT
CUTOFF
4. Turn over thermostat base and note the spring fingers
that engage the subbase contacts. Make sure the spring
fingers are not bent flat. Flat fingers prevent proper electrical
contact with the subbase.
5. Set the second stage heat anticipation indicator to
match the current rating of the controlled equipment. See
Heat Anticipator Setting section. The first stage heat antici-
pator and the cooling anticipator are nonadjustable.
6. Note the two tabs on the top inside edge of the
thermostat base. The tabs fit into corresponding slots on top
of the subbase. Mount the thermostat on the subbase.
7. Align the two captive mounting screws in the thermo-
stat base with the posts on the subbase (Fig. 9). Tighten both
screws. Do not overtighten screws because damage to
subbase posts can result.
Fig. 8—LED space location and adjustable lever
stops.
TIGHTENING SCREW
ADJUSTABLE STOPS
LED SPACE
M7557
60-1147-4
6
Fig. 9—Mounting thermostat on subbase.
THERMOSTAT
MOUNTING POST (2)
M936
50 60 70 80
50 60 70 80
HEAT
COOL
THERMOSTAT
MOUNTING SLOTS (2)
SUBBASE
THERMOSTAT
CAPTIVE MOUNTING
SCREWS (2)
Settings
HEAT ANTICIPATOR SETTING
Set the adjustable heat anticipator to match the current
draw of the second stage heating primary control (Fig. 10). If
the primary control nameplate has no rating or if further
adjustment is necessary, use the following procedure to
determine the current draw of the second stage.
NOTE: The current draw of the heating stage must be measured
with the thermostat removed and the power on.
1. Connect an ac ammeter of appropriate range between
the W2 and R terminals on the subbase.
2. Move the system switch to HEAT or AUTO.
3. After one minute, read the ammeter and record the
reading.
4. After mounting the thermostat, set the adjustable heat
anticipator to match the reading measured in step 3.
Fig. 10—Stage two adjustable heat anticipator.
1.2
.4
.6
.3
.2
.15
.12
.10
.8
MOVE INDICATOR
TO MATCH CURRENT
RATING OF PRIMARY CONTROL
M3684
TEMPERATURE SETTING
Fig. 11—Location of external components (T874N
shown).
HEAT
COOL
M3525
50 60 70 80
50 60 70 80
50 60 70 80
OFF
AUTO
FAN
HEATON
AUTO
COOL
AUX RELAY
HEATING
SET POINT
LEVER
COOLING
SET POINT
LEVER
THERMOMETER
(WHEN PROVIDED)
FAN
SWITCH
SYSTEM
SWITCH
OPTIONAL LED
ENUNCIATION
XXX
XXXXXXXXXXXX
XXX
XXXX
The T874N has separate heating and cooling set point
levers; the T874R has one set point lever for heating and
cooling. Move the heating and cooling set point levers (Fig.
10) to the desired comfort positions. The minimum differen-
tial between heating and cooling set point is 3° F [2° C] on the
T874N.
SUBBASE SETTING
A description of the subbase switching positions that
control the system operation follows (Fig. 11).
SYSTEM SWITCH (some subbases do not have all of the
following functions):
OFF: Both the heating and cooling systems are off. If the
fan switch is in AUTO position, the cooling fan is also
off.
AUTO: Thermostat automatically changes between heat-
ing and cooling system operation, depending on the
indoor temperature.
HEAT: Heating system is automatically controlled by the
thermostat. Cooling system is off.
COOL: Cooling system is automatically controlled by the
thermostat. Heating system is off.
EM. HT.: Emergency heat relay is automatically con-
trolled by the thermostat. Cooling system is off.
FAN SWITCH
ON: Fan operates continuously.
AUTO: Fan operates automatically with heating and
cooling equipment as controlled by the thermostat.
To move the subbase switches to the desired control
positions, use thumb and index finger to slide lever. Lever
must stop over desired function indicator position for proper
circuit operation.
60-1147-47
Checkout
HEATING
Move the system switch on the Q674 to HEAT or AUTO
(if used) and the fan switch to AUTO. Move the heating set
point lever on the T874 about 10° F [6° C] above room
temperature. Heating equipment should start and the fan
should run. Move the heat lever about 10° F [6° C] below
room temperature. The heating equipment and fan should
shut off.
NOTE: In heat pump applications, time delays are involved
before the compressor is activated to prevent short cy-
cling. The delays are provided by a timer, which prevents
the compressor from starting for several minutes after the
thermostat last turned the compressor off, or after the
system first received power.
COOLING
Move the system switch on the Q674 to COOL or AUTO
(if used) and the fan switch to AUTO. Move the cooling set
point lever on the T874 about 10° F [6° C] below room
temperature. The cooling equipment should start (see NOTE
above). Move the cool lever about 10° F [6° C] above room
temperature. The cooling equipment and fan should shut off.
FAN
Move the subbase system switch to OFF, and the fan
switch to ON. The fan should run continuously. Move the fan
switch to AUTO. In this position, fan operation is controlled
by the heating or cooling system control circuit.
Calibration
THERMOSTAT
T874 Thermostats are accurately calibrated at the factory.
They do not have provision for field calibration.
THERMOMETER
The thermometer in your thermostat has been accurately
calibrated at the factory. The thermometer should need
adjustment only if it has been dropped or shifted due to
mishandling.
If the set point lever and the thermometer reading do
not agree:
1. Remove the thermostat cover by pulling up from the
bottom of cover until it clears the mounting slots.
2. Set the thermostat cover on a table near an accurate
thermometer.
3. Allow 10 or 15 minutes for cover thermometer to
sense area temperature; compare the readings. Be careful
not to touch the thermometer or breathe on it.
4. If the readings are the same, replace the cover and put
the system into operation.
5. If the readings are different, insert a small screw-
driver in the thermometer slot (Fig. 12) and turn it until the
thermometers have the same reading.
6. Replace thermostat cover and put the system into
operation.
NOTE: Radiant heat from your hands will offset the ther-
mometer reading. After making each adjustment, wait 10
or 15 minutes for the thermometer to stabilize before
comparing.
Fig. 12—Thermometer calibration.
M5070
60-1147-4
8
Honeywell Limited-Honeywell Limitée
35 Dynamic Drive
Scarborough, Ontario M1V 4Z9
60-1147 –4 S.M. Rev. 5-93
Automation and Control Solutions
Honeywell International Inc.
1985 Douglas Drive North
Golden Valley, MN 55422
www.honeywell.com/yourhome
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Honeywell T874/Q674 User manual
- Category
- Thermostats
- Type
- User manual
- This manual is also suitable for
Honeywell Thermostat T874/Q674 offers precise temperature control for heat pump systems. With its two-stage heating and one-stage cooling operation, it ensures efficient and comfortable temperature management. Advanced features include LED indicators for system status, automatic changeover between heating and cooling modes, and adjustable fan settings for optimal airflow. The thermostat's intuitive interface allows for easy programming and operation, making it a reliable choice for maintaining a comfortable indoor environment.
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