Honeywell T874Q674 Thermostat User Manual

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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/  
Subbasea  
Model  
Number  
of Stages  
Changeover  
Stage  
Type of Switching  
System  
Heating  
Cooling  
Heating  
Cooling  
Fan  
See Fig.  
T874N/Q674C  
T874N/Q674F  
2
2
1
1
1
—
1
OFF-AUTO  
AUTO-ON  
AUTO-ON  
5
6
—
OFF-EM. HT.-  
HEAT-AUTO-COOL  
T874R/Q674L  
2
1
—
2b  
EM. HT.-HEAT-  
OFF-COOL  
AUTO-ON  
7
a
Q674 Subbase provides the wiring terminals, system switch and fan switch for system operation.  
Provides manual changeover with the subbase system switch in COOL position.  
b
Operation  
Installation  
On a two-heat thermostat, the two stages of heat make  
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.  
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  
checkedordonetomaintainefficientoperationofthesystem.  
See your heating system instructions for the specific mean-  
ing.  
TheEM.HT.LEDlightswhenthesystemswitchisplaced  
in the EM. HT. position. Emergency heat is operating; in  
most systems, the compressor has failed and the heat pump  
is not operating.  
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. Topreventinterferencewiththethermostatlink-  
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.  
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.  
3
. Donotovertightenthermostatcaptivemounting  
screwsbecausedamagetosubbasethreads may  
result.  
Recycling Notice  
4
. Do not short across coil terminals on the relay.  
This may burn out the thermostat heat  
anticipator.  
This control contains mercury in a sealed tube. Do not  
place control in the trash at the end of its useful life.  
Ifthiscontrolisreplacingacontrolthatcontainsmercuryin  
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.  
IMPORTANT: Thermostats are calibrated at the factory  
using subbases mounted at true level. An inaccurately  
leveled subbase will cause thermostat control devia-  
tion.  
If you have questions, call Honeywell at 1-800-468-1502.  
S. M. • Rev. 5-93 •  
M• ©Honeywell Inc. 1993 • Form Number 60-1147—4  
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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:  
Fig. 1—Installation of Q674 Subbase on outlet box.  
VERTICAL  
OUTLET  
BOX  
1
—
—
—
—
—
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.  
COVER  
PLATE  
ADAPTER  
2
RING  
2
MOUNTING  
SCREWS (2)  
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,  
SUBBASE  
order 193121A Adapter Assembly (Fig. 1). The as-sembly  
includesanadapterring,twoscrewsandacoverplatetocover  
marks on the wall. Install the ring and cover plate on the  
vertical outlet box.  
MOUNTING  
SCREWS (2)  
HORIZONTAL  
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.  
OUTLET  
BOX  
1
MOUNTING  
SCREWS (2)  
SUBBASE  
NOT INCLUDED WITH UNIT.  
1
2
ACCESSORY PARTS AVAILABLE (193121A).  
M925  
2
. Pullwiresthroughthecoverplate(ifused)andsubbase  
cable opening (Fig. 3).  
. 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 Fig.  
, and firmly tighten the subbase mounting screws. The  
3
Fig. 2—Installation of Q674 Subbase on wall.  
4
3
WALL  
subbase mounting holes provide for minor out-of-level ad-  
justments.  
WIRES THROUGH  
WALL OPENING  
IMPORTANT: An incorrectly leveled subbase will cause  
the temperature control to deviate from set point.  
WIRING THE SUBBASE  
IMPORTANT:Use18-gaugecolor-codedthermostatcable  
WALL  
ANCHORS  
for proper wiring.  
(2)  
MOUNTING  
HOLES  
Disconnectpowersupplybeforebeginninginstallationto  
prevent electrical shock or equipment damage.  
SUBBASE  
All wiring must comply with local electrical codes and  
ordinances. Follow equipment manufacturer wiring instruc-  
tions when available. To wire subbase, proceed as follows:  
MOUNTING  
SCREWS (2)  
M926  
1
. Connect the system wires to the subbase as shown in  
Fig. 3—Subbase components and leveling  
procedure.  
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).  
TOP MOUNTING HOLES (2)  
WIRING  
TERMINAL  
2
. Firmly tighten each terminal screw.  
THERMOSTAT  
3. Fit wires as close as possible to the subbase. Push  
SPIRIT LEVEL  
CABLE OPENING  
excess wire back into the hole.  
. Plug hole with nonflammable insulation to prevent  
4
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:Thecoverishingedatthetopandmustbere-moved  
by pulling outward at the bottom.  
MOUNTING HOLES (2)  
TO SPRING FINGER CONTACTS  
ON THE THERMOSTAT  
UP TO 12)  
POST (2) FOR  
MOUNTING  
THERMOSTAT  
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M927  
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2
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2
. Carefullyremoveanddiscardthepolystyrenepacking  
insert that protects the mercury switches during shipment.  
. IfLEDindication(EM.HT., CHECK, etc.)istobeused  
with the Q674 Subbase, install the preprinted insert under the  
thermostat set point scale (Fig. 8). To install, push both  
thermostatsetpointleverstothefarendsofthethermostat.Use  
index finger to gently pull out the plastic set point scale about  
Fig. 4—Wiring connections.  
3
FOR STRAIGHT  
INSERTION–  
STRIP 5/16 in. [8 mm]  
FOR WRAPAROUND–  
STRIP 7/16 in. [11 mm]  
1
/4 in. [6 mm]. Drop insert into recessed area behind set point  
scale so that selected LEDs show. Make sure insert is com-  
pletelyseatedinrecessedarea.Letsetpointscalepopback,and  
set levers to desired positions.  
BARRIER  
SUBBASE TERMINAL SCREW  
M928  
Fig. 5—Internal schematic and typical wiring diagram for T874N and Q674C.  
L1  
L2 (HOT)  
1
DEFROST RELAY  
CONTACT  
W1  
REVERSING  
RELAY  
OUTDOOR  
THERMOSTAT  
EM. HT. RELAY  
CONTACT  
HEAT  
RELAY 2  
H1  
ANTICIPATOR  
W3  
G
FALL  
FALL  
FAN  
SWITCH  
EM. HT. RELAY  
CONTACT  
HEAT  
RELAY 3  
H1  
H2  
AUTO  
ON  
FAN RELAY  
R
H2 ANTICIPATOR  
W2  
HEAT  
RELAY 1  
SYSTEM  
SWITCH  
X
OFF  
CHECK  
LED  
(GRN)  
C1  
ANTICIPATOR  
AUTO  
OPTIONAL  
COMPRESSOR  
FAILURE  
L
DEVICE  
C1  
CO  
RISE  
Y
COMPRESSOR  
CONTACTOR  
M1860  
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS  
REQUIRED.  
3
60-1147-4  
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Fig. 6—Internal schematic and typical wiring diagram for T874N and Q674F.  
W1  
OUTDOOR  
THERMOSTAT  
DEFROST  
RELAY  
REVERSING  
VALVE  
H1  
ANTICIPATOR  
EM.HT. RELAY  
CONTACT  
HEAT  
RELAY 2  
EM.HT. RELAY  
CONTACT  
HEAT  
RELAY 3  
H1  
FALL  
W3  
FAN SWITCH  
AUTO  
FAN RELAY  
H2  
G
R
ANTICIPATOR  
ON  
1
L1  
HOT  
L2  
H2  
FALL  
W2  
E
HEAT  
RELAY 1  
SYSTEM  
SWITCH  
EM. HEAT  
LED (RED)  
OFF  
EM. HEAT  
RELAY  
X
L
EM. HT.  
CHECK  
LED  
(GREEN)  
OPTIONAL  
COMPRESSOR  
FAILURE DEVICE  
HEAT  
AUTO  
RISE  
C1  
HIGH  
PRESSURE  
SWITCH  
COMPRESSOR  
CONTACTOR  
ANTICIPATOR  
COOL  
C1  
1
C0  
Y
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
M3686  
6
0-1147-4  
4
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Fig. 7—Internal schematic and typical wiring diagram for T874R and Q674L.  
L1  
HOT  
R
EM.HT. RELAY  
CONTACT  
L2  
1
EM.HT. RELAY  
CONTACT  
HEAT  
CONTACTOR 3  
W3  
H1/C1  
ANTICIPATOR  
OUTDOOR  
THERMOSTAT  
HEAT  
CONTACTOR 2  
DEFROST  
RELAY  
HEAT  
RELAY 1  
HIGH LIMIT  
SWITCH  
W2  
H1  
C1  
DEFROST  
RELAY  
REVERSING  
VALVE  
FALL  
B
L
FAN SWITCH  
OPTIONAL COMP  
FAILURE DEVICE  
AUTO  
ON  
AUX. HEAT  
LED (GREEN)  
H2  
H2  
X2  
ANTICIPATOR  
FALL  
X1  
E
SYSTEM  
SWITCH  
EM. HEAT  
LED (RED)  
EM. HEAT  
RELAY  
EM. HT.  
FAN RELAY  
HEAT  
OFF  
G
LOW  
AMBIENT  
CUTOFF  
COMPRESSOR HIGH  
CONTACTOR  
PRESSURE  
SWITCH  
COOL RELAY  
COOL  
Y
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS  
AND OVERLOAD PROTECTION AS REQUIRED.  
O
M3685  
4
. Turn over thermostat base and note the spring fingers  
Fig. 8—LED space location and adjustable lever  
stops.  
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  
TIGHTENING SCREW  
LED SPACE  
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.  
ADJUSTABLE STOPS  
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.  
M7557  
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.  
5
60-1147-4  
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TEMPERATURE SETTING  
Fig. 9—Mounting thermostat on subbase.  
Fig. 11—Location of external components (T874N  
shown).  
THERMOSTAT  
MOUNTING SLOTS (2)  
HEATING  
SET POINT  
LEVER  
OPTIONAL LED  
ENUNCIATION  
COOLING  
SET POINT  
LEVER  
THERMOSTAT  
MOUNTING POST (2)  
HEAT  
XXX  
XXX  
COOL  
XXXX XXXX XXXX XXXX  
50  
60 70 80  
50 60 70 80  
COOL  
50  
60 70 80  
50 60 70 80  
50  
60 70 80  
HEAT  
SUBBASE  
THERMOSTAT  
FAN  
AUTO  
ON  
OFF COOL AUTO HEAT AUX RELAY  
CAPTIVE MOUNTING  
SCREWS (2)  
M936  
THERMOMETER  
WHEN PROVIDED)  
FAN  
SWITCH  
SYSTEM  
SWITCH  
(
M3525  
Settings  
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.  
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.  
1
0) to the desired comfort positions. The minimum differen-  
tialbetweenheatingandcoolingsetpointis3°F[2°C]onthe  
T874N.  
SUBBASE SETTING  
A description of the subbase switching positions that  
control the system operation follows (Fig. 11).  
NOTE:Thecurrentdrawoftheheatingstagemustbemeasured  
with the thermostat removed and the power on.  
SYSTEMSWITCH(somesubbasesdonothaveallofthe  
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:Thermostatautomaticallychangesbetweenheat-  
ing and cooling system operation, depending on the  
indoor temperature.  
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.  
HEAT:Heatingsystemisautomaticallycontrolledbythe  
thermostat. Cooling system is off.  
COOL:Coolingsystemisautomaticallycontrolledbythe  
thermostat. Heating system is off.  
Fig. 10—Stage two adjustable heat anticipator.  
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.  
1
.2.8  
MOVE INDICATOR  
TO MATCH CURRENT  
RATING OF PRIMARY CONTROL  
M3684  
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If the set point lever and the thermometer reading do  
not agree:  
. Remove the thermostat cover by pulling up from the  
bottom of cover until it clears the mounting slots.  
. Set the thermostat cover on a table near an accurate  
thermometer.  
Checkout  
1
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.  
2
(
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.  
. If the readings are different, insert a small screw-  
5
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.  
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.  
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.  
Fig. 12—Thermometer calibration.  
FAN  
Move the subbase system switch to OFF, and the fan  
switchtoON.Thefanshouldruncontinuously.Movethefan  
switch to AUTO. In this position, fan operation is controlled  
by the heating or cooling system control circuit.  
Calibration  
THERMOSTAT  
T874Thermostatsareaccuratelycalibratedatthefactory.  
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.  
M5070  
7
60-1147-4  
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Automation and Control Solutions  
Honeywell International Inc.  
Honeywell Limited-Honeywell Limitée  
35 Dynamic Drive  
1
985 Douglas Drive North  
Golden Valley, MN 55422  
Scarborough, Ontario M1V 4Z9  
6
0-11 4 7– 4 S.M. Rev. 5-93  
www.honeywell.com/yourhome  

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