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PROTECTION A WSU
Fig. 14-Typical hookup for T874R1251/0674L1272.
ClFig. ---Ty kl DIoSp WIr T WI4G14 44 AND OVLOA13.
AI6 AM PROnTECnOW AS EQUIRED.
Fig. 15-Tyicdi hookup for T974G14021O674L1363.
Fig. 10-Typical hookup for T874D1645/0674E1288.
DO NOT USE standard screws that provide
metal-to-metal contact with the stop brackets.
Short circuit and potential equipment damage
System switching positions control thermostat oper-
ation as follows:
OFF-heating and cooling systems are off. If the fan
switch is at the AUTO position, the cooling fan is
HEAT-heating system is controlled by the thermo-
stat Cooling system is off.
AUTO-thermostat automatically switches between
heat and cool modes, depending upon the indoor
COOL-thermostat controls the cooling system.
Heating system is off.
EM.HT.-emergency heat relay is energized on call
for heat. Cooling system is off. Compressor is
Fan switching positions control fan operation as
ON-fan operates continuously.
AUTO-fan operates as controlled by the thermostat
in heat pump systems, or conventional cooling
mode; fan operates as controlled by plenum
switch in conventional heating mode.
To switch positions, use thumb and index finger to
slide lever to desired position. Switch lever must stop in
detent directly over desired function indicator mark for
proper circuit operation.
Move the system switch on the Q674 Subbase to
HEAT or AUTO. Move the heating lever on the T874
about 10* F [5.6 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
[5.6* C] below room temperature. The heating equip-
ment should shut off.
Do not operate cooling if outdoor temperature is
below 50* F [10* C]. Refer to manufacturer's
Move the system switch on the Q674 Subbase to
COOL or AUTO. Move the cooling lever on the T874
Thermostat about 10* F [5.6* C] below room tempera-
ture. The cooling equipment and fan should start. Move
the cooling lever about 10* F [5.6 C] above room
temperature. The cooling equipment and fan should
Move the system switch to EM.HT. The EM.HT. LED
should come on. Move the lever about 10* F (5.6* C]
above room temperature. The electric strip heater(s)
should come on. Move the lever about 10* F [5.6* C]
below room temperature. The electric strip heater
should de-energize. The EM.HT. LED will remain on
until system switch is moved to another position.
Move the subbase system switch to OFF or AUTO,
and the fan switch to ON. The fan should run con-
tinuously. When the fan switch is in the AUTO position,
fan operation is controlled by the heating or cooling
Fig. &-U" MUW WWW"d.
Fig. 7-Typlal hookup for T$74D/0I74B.
/ JU8ER RE-IRM FOR SINGLE TRANSFOMER.
/A TERMINAL OTDR IO. IA.I4A
Fig. 8-Typical hookup for T874D/Q6740.
Fig. 9-Typicald hookup for TI7401296/Q67401032.
SETTING THE HEAT ANTICIPATOR
Set each adjustable heat anticipator to match its
primary control current draw. If the primary control
nameplate 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 from the
subbase and the power on.
1. Connect an ac 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
4. After mounting the thermostat, set the adjustable
heat anticipator(s) to match the respective readings)
measured in step 3 (Fig. 18).
MOVE INDIATOR TO
MATCH CURRENT RATING
0504 OF PRIMARY CONTROL
Fig. 18-Adjustable heat anticipator scales.
INSERTION- FOR WRAPAROUNDO
STRIP 5./16.n1 i -TRIP 7/16m [11 m
Fig. 16-Barrier configuration.
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 and must be
removed by pulling up at the bottom.
2. Carefully remove and discard the polystyrene
packing insert which protects the mercury switches
3. If thermostat is being used with a 0674 Subbase
which has LED indication, and the thermostat set point
scale does not have designations preprinted (EM. HT.,
AUX. HT., etc.), install the desired preprinted insert
packed with the subbase. Push thermostat set point
lever(s) 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. Reposition
set point lever(s).
4. Turn the thermostat base over and note the spring
fingers which engage the subbase contacts. Make sure
the spring fingers are NOT bent flat, preventing proper
Fig. 17-Mounting thermostat on subbase.
Move the heating and cooling levers to the desired
positions. The minimum differential between heating
and cooling set points is 3* F [1.7 C], which means the
thermostat is made so the levers cannot be set closer
together than 3* F [1.7* C].
NOTE: Heating and cooling is controlled by a single set
point lever on the T874R.
If adjustable lever stops are desired (Fig. 19), order
4074ECK Envelope Assembly, containing 2 adjustable
lever stop brackets, 1 brass insert, 1 mounting screw
and 2 locking screws with insulated heads. When in-
stalled, the stop brackets will limit the movement of the
T874 HEAT and COOL levers.
The adjustable lever stop brackets should be in-
stalled only if there is a need to restrict the heating and
cooling temperature control points. To install-
1. Turn to the back of the T874 thermostat Locate
the hole for brass insert in the plastic base below the
2. Push brass insert into the hole with your finger.
3. Turn to front of the T874 thermostat
4. Place the 2 stop brackets in position with their
tabs in the slot between the HEAT and COOL levers
5. Insert the mounting screw into the 2 slots in the
stop brackets and attach to the brass insert Tighten the
screw to pull the brass insert into back of thermostat
6. Loosen the mounting screw enough to free the
stop brackets for adjustment
7. Move the HEAT and COOL levers to the maximum
temperature that Is desired.
8. Slide the stop brackets until one rests against the
HEAT lever and the other against the COOL lever.
Firmly tighten the mounting screw.
9. If the HEAT and COOL levers are to be locked in
place at a specific temperature, use the 2 insulated
head screws supplied instead of the 2 adjustable lever
/POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PRO-
TECTION AS REQUIRED.
electrical contact with the subbase.
5. Set the heat anticipator indicators (that are adjust-
able) to the respective current settings of each stage.
See Setting the Heat Anticipator.
6. Note the tabs along the top inside edge of the
thermostat base. The tabs fit into the subbase notches.
Mount the thermostat base on the subbase and tighten
the captive mounting screws. See Fig. 17.
7. Place the upper edge of thermostat cover on
thermostat base and swing cover downward until it
engages with cover clip on base.
i. n you must mount the subbase on a vertical outlet
box, order Part No. 193121A Adapter Assembly (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.
For a wall installation, hold subbase in position and
mark holes for anchors (Fig. 2). Wall anchors must be
obtained from local hardware store. Take care that the
wires do not fall back into the wall opening. Set
subbase aside. Drill four 3/16 in. [4.8 mm] holes and
gently tap anchors into the holes until flush with the
Fig. 2-Installation of subbase on wall.
2. Pull wires through the cover plate (if used) and
.ubbase cable opening (Fig. 3).
3. Secure the cover plate (if used) and subbase with
Ine screws provided. Do not fully tighten the subbase
4. Level the subbase using a spirit level, as shown in
Fig. 3, and firmly tighten subbase mounting screws. The
subbase mounting holes provide for minor out-of-level
A subbase incorrectly leveled will cause the
temperature control to deviate from set point.
5. Connect the system wires to the subbase as
shown in Figs. 7-15. A letter code is near each terminal
for identification. The terminal barrier permits straight or
conventional wraparound wiring connections (Fig. 16).
Either method is acceptable. Run wires as close to the
subbase as possible, keeping wire length to a minimum.
Push excess wire back into the hole. Plug hole to
6. Your 0Q674 subbase may require one or more
jumpers that may or may not be factory supplied. Use
the table and illustrations below for proper installation.
Never install more than one wire per terminal unless
factory supplied jumper with spade terminal is used.
IF YOUR SUBBASE USE
HAS: APPLICATION FIG.
RC, RH terminals single transformer 4
adjacent terminals special system 5
nonadjacent terminals or LED indication 6
OUTDOOR RESET THERMISTOR THERM
(T874R1251/Q674L1272 only) RSTA
This system is supplied with a Honeywell C815A1039 4
Thermistor in the outdoor section. The thermistor must im
be used; if not, thermostat performance will deviate oo
radically from proper operation.
The proper thermistor operation must be verified to 2
insure the correct operation of the thermostat. Check 400
thermistor operation as follows: 200
1. Disconnect the "T" wire on the subbase.
2. Use an ohmmeter to measure resistance between $o10
the "T" wire and the "X" subbase terminal.
3. Take outdoor temperature at thermistor location
and find the correct thermistor resistance on chart in o00
Fig. 20. 4"
4. If the resistance measured in step 2 and the
calculated resistance in step 3 vary by more than 15
percent, the thermistor requires replacement. Contact
installing dealer for replacement packaged outdoor
T874 Thermostats are accurately calibrated at the
factory. THEY DO NOT HAVE PROVISION FOR FIELD
1. Remove thermostat cover by pulling up from the
bottom of cover until it clears the cover clip.
2. Set the cover on a table near an accurate
3. After allowing 10 or 15 minutes for stabilization,
compare the readings. If they are the same, replace
cover and put system into operation. If they are differ-
ent, recalibrate the thermostat thermometer, step 4.
4. Insert a small screwdriver in the thermometer shaft
(Fig. 21) and turn it until the thermometers read the -
same. When the thermometer is calibrated, replace
cover and place system into operation.
NOTE: Hand heat will offset the thermometer reading.
After making each adjustment, wait 10 or 15 minutes -
for the thermometer to stabilize before comparing.
Fig. 21-Thermometer calibration.
HonewelIn. International Sales Offices In al principal cities of the world. Manufacturing in
1885 Douglas Drive N Australia. Canada. Finland. France, Germany, Japan, Mexico. Netherlands,
Golden Valley, MN 55422-4388 Spain. Talwan, United Kingdom. USA PRINTED IN U.SA. IMQAIeKE M
I I I I
TEMPERATURE OF THERMISTOR F inF
Fig. 20-Thermistor resistance chart.
Fig. 4-Jumper RC and RH for single transformed
system. Strip wire 3/4 In. [19 mm].
A O ADJACENT TERMINALS SHOWN JUMPERED ARE FOR EXAMPLE ONLY.
COMPARE WIRING DIAGRAM *AN SUB8ASE TO IDEPITIFY TERMINALS TO
BEJUMPERED. I.e t
Fig. 5-Strip wire 3/4 in. [19 mm].
INSTALLATION INSTRUCTIONS FO'IT
The T874D,G,R Multistage Thermostats provide 24 to
30 Vac control for heating and/or cooling systems as
T874D T874G T874R
Heating Stages 2 2 2
Cooling Stages 2 1 1
Changeover Stages 1 -
HONEYWELL T874D,G,R MULTISTAGE
(for York International)
HE TRAINED SERVICE TECHNICIAN
0674 SWITCH POSITIONS
MODEL SYSTEM FAN
B HEAT-OFF-COOL AUTO-ON
D None None
E OFF-HEAT-AUTO- AUTO-ON
F OFF-COOL-AUTO- AUTO-ON
J EM.HT.-AUTO-OFF AUTO-ON
The 0674B,D,E,F,J,L Subbases provide wiring ter- L EM.TI.-HEAi-i-F- UIU-UIO
minals, and system and fan switching as follows. ______COOL
On a 2-heat thermostat, the two stages of heat the system switch is placed in the EM.HT. position by
"make" sequentially as the temperature drops. "Make" the homeowner.
refers to the mercury switch initiating a call for heat or If your subbase model includes a green AUXILIARY
cool. HEAT LED, it will light up when the auxiliary heat
There is about 20 F [1.1 between stages so that (second stage) is operating. The heating load is great
the second stage makes only when the first stage can't enough that the heat pump cannot handle the load
handle the load. This is the interstate differential, alone.
If your subbase model includes a red EM.HT. LED
(light emitting diode), it will light up when the emer- If your subbase model includes a red SERVICE LED,
agency heat is operating. The homeowner should switch it will light up when the system needs service. See
to EM.HT. when the compressor has malfunctioned and heating system instructions for specific meaning.
the heat pump isn't operating. The LED will light when LEDs are not field replaceable or addable.
WHEN INSTALING THIS PRODUCT... -concealed pipes and chimneys.
1. Read these instructions carefully. Failure to follow -unheated uncooledd) areas behind the thermostat,
them could damage the product or cause a hazardous such as an outside wall.
2. Check the ratings given in the instructions and on
the product to make sure the product is suitable for
3. Installer must be a trained, experienced service
4. After installation is complete, check out product
operation as provided in these instructions.
1. Disconnect power supply to prevent electrical
shock or equipment damage.
2. Run wires as close to the subbase as possible.
To prevent interference with the thermostat
linkage, keep wire length to a minimum. Push
excess wire back into the hole, and plug hole
to prevent drafts from affecting thermostat
3. Do not overtighten thermostat captive mount-
ing screws as damage to subbase threads
4. Do not short across coil terminals on relay.
This may bum out the heat anticipator.
Install the thermostat about 5 ft [1.5 m] above the floor
in an area of good circulation at average temperature.
Do not install the thermostat where it may be affected
-drafts, or dead spots behind doors and in comers.
-hot or cold air from ducts.
-radiant heat from sun or appliances.
MOUNTING AND WIRING THE SUBBASE
The thermostat subbase can be mounted on a
vertical outlet box, horizontal outlet box, or directly on
V E j i C Box L0
Fonr Number 60-1155-4
*Honeywell Inc. 1987
F 1\ NOT INCLUDED WITH UNIT
ACCESSORY PARTS AVAILABLE (193121A).
Fig. 1-ln-talalon of 0674 Subbaese on oulle box.