Page 1
T834B; T834C; T834J
Heating-Cooling Thermostats
INSTALLATION INSTRUCTIONS
APPLICATION
The T834B,C,J Heating-Cooling Thermostats provide 24
to 30 Vac control in heating-cooling systems. An spdt
mercury switch makes R to W on a temperature fall for
heating, and R to Y on a temperature rise for cooling.
Integral switches control HEAT-OFF-COOL or COOL-OFF
system operation and AUTO-ON or ON-AUTO fan
operation (fan switch on T834C,J only). In heat pump and
some electric heat systems, fan operation is controlled by
the thermostat during heating. Check the electric heat
manufacturer specifications for fan control requirements. If
fan control from the thermostat is necessary in an electric
heat application, use the T834C Thermostat model (dual
fuel) with optional fan control. Jumper terminals 1 and 2 to
control fan operation from the thermostat during heating.
R
2
1
W
IN ELECTRIC HEAT AND HEAT PUMP APPLICATIONS, JUMPER
1
TERMINALS 1 AND 2 FOR AUTOMATIC FAN CONTROL IN HEATING
AND COOLING.
2
IN GAS-AND OIL-FIRED APPLICATIONS, JUMPER TERMINALS 1
AND Y FOR AUTOMATIC FAN CONTROL IN COOLING.
Fig. 1. Jumpering terminals for fan control.
G
Y
JUMPER
1
2
M8675
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 follow
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 product
operation as provided in these instructions.
CAUTION
Damage to Heating/Cooling System Possible.
Be careful when handling wires during
installation.
Disconnect power at furnace or at main breaker/
fuse before starting installation.
Location
Locate the thermostat about 5 ft (1.5m) above the floor on
an inside wall in an area with good air circulation at
average temperature.
Do not mount the thermostat where it may be affected by:
— drafts or dead spots behind doors or in corners.
— hot or cold air from ducts.
— radiant heat from the sun, fireplaces, or appliances.
®U.S. Registered Trademark
Copyright © 1999 Honeywell Inc. • • All Rights Reserved
X-XX UL
69-0444-10
Page 2
T834B; T834C; T834J HEATING-COOLING THERMOSTATS
Wiring and Mounting
Disconnect power supply before beginning installation to
prevent electrical shock or equipment damage.
All wiring must comply with local codes and ordinances.
The T834 may be mounted directly on a wall or vertical
outlet box. Use Honeywell part no. 193121A Mounting
Plate Assembly (ordered separately) to mount on horizontal outlet box or cover marks left by old thermostat. If
mounting plate assembly is used, review instructions
provided with assembly before wiring and mounting
thermostat.
To wire and mount thermostat:
1. In replacement applications, check the existing
thermostat wires for cracked or frayed insulation.
Replace any wires in poor condition. If the wire is
plastered into the wall, make a hole next to the
wires and loosen the wires so they can be
pushed back into the wall later.
2. In new installations, run wiring (if necessary) to the
thermostat location.
3. Connect the wires to the terminals on the back of
the thermostat. See Fig. 3 through 12 for
internal schematic and typical hookup diagrams.
If control of fan operation from the thermostat is
required in a central electric heat application,
jumper terminals 1 and 2. See Fig. 1.
4. Remove thermostat cover by pulling outward on
bottom edge of the cover until it snaps free of the
thermostat base. See Fig. 2. Carefully remove
and discard the foam plastic shipping insert that
protects the switch and bimetal assembly during
shipping.
5. Set the adjustable heat anticipator indicator to
match the current draw of the primary heating
control (see Heat Anticipator Setting section).
6. Push excess wire back through the hole and plug
any opening with insulation to prevent drafts that
may affect thermostat performance.
7. Loosely fasten the thermostat to the wall or outlet
box with a screw through the top mounting hole.
Adjust the thermostat so that it is approximately
level and start the second screw through the
bottom mounting hole. Do not tighten.
8. Level the thermostat exactly using a spirit level or
plumb line. Tighten the mounting screws.
IMPORTANT
An incorrectly leveled thermostat will cause the
temperature control to deviate from setpoint.
9. Replace the thermostat cover.
MOUNTING HOLE
(THERMOSTAT
TO WALL OR
OUTLET BOX)
.18
.9
.7
.2
.5
3
.25
FAN
SWITCH
1
TEMPERATURE
1 FAN SWITCH AVAILABLE ON T834C ONLY.
SETTING LEVER
BIMETAL ELEMENT
BEHIND SCALE
ADJUSTABLE HEAT
ANTICIPATOR
INDICATOR
SYSTEM
SWITCH
MOUNTING HOLE
Fig. 2. Internal view of T834.
M8676
FAN SWITCH
H1
H1
ANTICIPATOR
1
C1
TEMP. FALL
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
C1
ANTICIPATOR
AUTO
SYSTEM
SWITCH
COOL
OFF
HEAT
ON
HEAT
OFF
COOL
R
G
Y
W
FAN RELAY
COMPRESSOR
CONTACTOR
HEAT RELAY
Fig. 3. Internal schematic and typical hookup diagram for T834C in standard heating-cooling system.
69-0444—10 2
M1119A
L1
(HOT)
L2
1
Page 3
T834B; T834C; T834J HEATING-COOLING THERMOSTATS
FAN SWITCH
H1
H1
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
2
IN ELECTRIC HEAT APPLICATION, JUMPER 1 AND 2 FOR AUTO FAN IN HEATING.
H1
TEMP. FALL
H1
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
2
INSTALL JUMPER BETWEEN W AND Y TERMINALS
WHEN HEAT RELAY IS NOT USED.
C1
TEMP. FALL
C1
ANTICIPATOR
Fig. 4. Internal schematic and typical hookup for T834C dual fuel model
in a gas- or oil-fired, or central electric heat system.
C1
C1
ANTICIPATOR
ON
AUTO
SYSTEM
SWITCH
COOL
OFF
HEAT
FAN SWITCH
ON
AUTO
SYSTEM
SWITCH
COOL
OFF
HEAT
HEAT
OFF
COOL
HEAT
OFF
COOL
R
G
Y
B
O
W
R
G
1
Y
2
W
FAN RELAY
2
CHANGEOVER
RELAY (HEAT)
HEAT RELAY
FAN RELAY
2
COMPRESSOR
CONTACTOR
HEAT RELAY
COMPRESSOR
CONTACTOR
CHANGEOVER
RELAY (COOL)
M1037C
L1
(HOT)
L2
1
M2035A
L1
(HOT)
L2
1
Fig. 5. Internal schematic and typical hookup for T834C in heat pump system with supplementary heat.
HEAT
OFF
COOL
1
G
R
O
3
2
W
4
Y
B
FAN RELAY
2
HEAT RELAY
CHANGEOVER
RELAY (HEAT)
CHANGEOVER
RELAY (COOL)
COMPRESSOR
RELAY
FAN SWITCH
AUTO
ON
H1
C1
TEMPERATURE
FALL
H1
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT
MEANS AND OVERLOAD PROTECTION
AS REQUIRED.
2
JUMPER 1-Y FOR AUTO FAN IN COOLING ONLY.
3
JUMPER 1-2 FOR AUTO FAN WITH WAND Y.
4
JUMPER W-Y FOR SINGLE-STAGE HEAT PUMP.
Fig. 6. Internal schematic and typical hookup for T834C gas or oil-fired systems and single-stage
C1
ANTICIPATOR
SYSTEM
SWITCH
COOL
OFF
HEAT
heat pump or central electric heat.
3
L1
(HOT)
L2
1
M11342A
69-0444—10
Page 4
T834B; T834C; T834J HEATING-COOLING THERMOSTATS
FAN
SWITCH
H1
H1
ANTICIPATOR
1
C1
TEMP. FALL
C1
ANTICIPATOR
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
AUTO
SYSTEM
SWITCH
COOL
OFF
HEAT
ON
HEAT
OFF
COOL
R
G
Y
CHANGEOVER
RELAY (HEAT)
B
O
FAN RELAY
COMPRESSOR
CONTACTOR
CHANGEOVER
RELAY (COOL)
Fig. 7. Internal schematic and typical hookup for T834C in single-stage heat pump system.
FAN SWITCH
AUTO
SYSTEM
SWITCH
COOL
OFF
HEAT
ON
HEAT
OFF
COOL
H1
C1
TEMP. FALL
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
H1
ANTICIPATOR
C1
ANTICIPATOR
R
G
P
O
W
Y
B
HEAT RELAY
CHANGEOVER
RELAY (COOL)
COMPRESSOR
CONTACTOR
DEFROST
RELAY
CHANGEOVER
RELAY (HEAT)
FAN RELAY
M2108A
L1
(HOT)
L2
1
M412
L1
(HOT)
L2
1
Fig. 8. Internal schematic and typical hookup for T834C with terminal for defrost relay in heat pump system.
FAN
H1
C1
TEMP. FALL
C1
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
2
JUMPER RC AND RH IN ONE TRANSFORMER SYSTEMS.
SWITCH
AUTO
SYSTEM
SWITCH
COOL
HEAT
OFF
ON
HEAT
OFF
COOL
RC
G
FAN RELAY
Y
COOL RELAY
2
RH
HEAT RELAY
W
M11746
Fig. 9 . Internal schematic and typical hookup for T834C in two transformer system.
69-0444—10 4
L1
(HOT)
L2
1
L1
(HOT)
L2
1
Page 5
T834B; T834C; T834J HEATING-COOLING THERMOSTATS
M498
L1
(HOT)
L2
1
M6108A
L1
(HOT)
L2
1
NO FAN
H1
TEMP. FALL
H1
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
C1
C1
ANTICIPATOR
Fig. 10. Internal schematic and typical hookup for T834B in standard heating-cooling system
H1
H1
ANTICIPATOR
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
TEMP. FALL
C1
C1
ANTICIPATOR
SWITCH
SYSTEM
SWITCH
COOL
OFF
HEAT
HEAT
OFF
COOL
with no fan switching.
NO FAN
SWITCH
SYSTEM
SWITCH
HEAT
OFF
COOL
COOL
OFF
HEAT
R
Y
COMPRESSOR
CONTACTOR
HEAT RELAY
W
R
ZONE VALVE
W
G
FAN RELAY
COMPRESSOR RELAY
Y
Fig. 11. Internal schematic and typical hookup for T834B in heating-cooling system with zone valve.
FAN SWITCH
C1
TEMP. FALL
1
C1
ANTICIPATOR
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
AUTO
COOL
OFF
ON
SYSTEM
SWITCH
OFF
COOL
R
FAN RELAY
G
P
"P" RELAY
O
"O" RELAY
COOL RELAY
Y
Fig. 12. Internal schematic and typical hookup for T834J cooling only system.
5
M6109A
L1
(HOT)
L2
1
69-0444—10
Page 6
T834B; T834C; T834J HEATING-COOLING THERMOSTATS
SETTINGS AND ADJUSTMENT
System and Fan Switching
T834B
The T834B features a SYSTEM switch for control of the
heating-cooling system.
The SYSTEM switch controls system operation as follows:
HEAT: Heating system only operates.
OFF: Both heating and cooling control systems are
disconnected.
COOL: Cooling system only operates.
The fan operates in response to the plenum fan control in
heating; fan operates with cooling equipment in cooling.
T834C
The T834C features SYSTEM and FAN switches for
control of the heating-cooling and fan systems.
The SYSTEM switch controls system operation as follows:
HEAT: Heating system only operates.
OFF: Both heating and cooling control systems are
disconnected.
COOL: Cooling system only operates.
The FAN switch controls fan operation as follows:
AUTO: for conventional (gas, oil or central electric heat)
systems, the fan operates in response to the plenum
fan control in heating; fan operates in response to
the thermostat in cooling. For heat pump systems,
the fan operates in response to the thermostat in
both heating and cooling.
ON: The fan runs continuously.
T834J
The T834J features SYSTEM and FAN switches for
control of the cooling and fan systems.
The SYSTEM switch controls system operation as follows:
OFF: Cooling control system is disconnected.
COOL: Cooling system operates.
The FAN switch controls fan operation as follows:
AUTO: Fan operates in response to the thermostat in
cooling.
ON: Fan runs continuously.
NOTE: Some electric heat systems require control of fan
operation from the thermostat. These systems
require a thermostat with control of fan operation
in response to a call for heating or cooling.
To switch positions, use thumb and index finger to slide
lever to desired position. Switch lever must stop directly
over desired function indicator mark for proper circuit
operation.
Temperature Setting
Push the temperature setting lever to the desired control
point on the temperature scale. The same lever controls
both heating and cooling. On models with temperature
range stops, temperature setting lever can be moved only
between the two temperature range stops.
HEAT ANTICIPATOR SETTING
IMPORTANT
The T834 Thermostat has an adjustable heat
anticipator and will operate properly ONLY IF
THE ANTICIPATOR IS ADJUSTED TO MATCH
THE CURRENT DRAW OF THE PRIMARY
CONTROL. Use this thermostat only on systems
with current draws that fall within the range of the
heat anticipator. Do not use this device on
Powerpile® (millivolt) Systems.
Conventional Systems
A current rating is usually stamped on the nameplate of
the primary control. Set the adjustable heat anticipator
indicator to match the value given on the nameplate.
If the current rating is not available, proceed as follows to
determine the rating:
1. Turn off power.
2. Wire thermostat, except for connection to
W terminal, but do not mount it on the wall.
3. Connect ammeter between W wire and
W terminal on the thermostat.
4. Prepare the system for operation.
5. Turn on power.
6. Turn system switch to heat.
7. Increase thermostat setpoint as necessary to get
system operating.
8. With the system operating through the ammeter,
wait one minute, then read the ammeter.
9. Turn the system switch to OFF, and turn off
power.
10. Adjust the heat anticipator to match the reading
on the ammeter.
11. Disconnect the ammeter, reconnect the W wire,
and mount the thermostat. Continue with system
checkout.
NOTE: The heat anticipator may require further adjust-
ment for best performance. To lengthen burneron time, move the indicator in the direction of the
longer arrows but not more than one-half scale
marking at a time. To shorten burner-on time,
move indicator in opposite direction.
Heat Pump Systems
(for about 3 cycles per hour)
Using B Terminal
Set adjustable anticipator to 130 percent of combined
current draw of compressor and fan relays.
Using O Terminal
Set adjustable anticipator to maximum scale setting. Limit
combined load current of compressor and fan relays to
0.8 amp, because cooling anticipator provides anticipation
during heat cycle in these hookups.
69-0444—10 6
Page 7
T834B; T834C; T834J HEATING-COOLING THERMOSTATS
Electric Systems (with auto fan in heat)
Set adjustable anticipator to combined current draw of
heating and fan relays.
Other Systems (without auto fan in heat)
Set adjustable anticipator to current draw of heat relay
or valve.
CHECKOUT
CAUTION
Damage To Heat Anticipator Possible.
Shorting across terminals of system controls
may cause damage to the heat anticipator.
Do not check operation by shorting across
terminals of systems controls.
IMPORTANT
To assure accurate temperature control, do not
touch or breathe on bimetal or thermometer.
Heating
With system switch set at HEAT and fan switch, if applicable, at AUTO, move the temperature setting lever about
10°F (6°C) above room temperature.
Conventional (gas, oil or central electric heat) systems:
heating should start and fan should start after a
short delay.
Heat pump systems: both heating and fan should start.
Move temperature setting lever 10°F (6°C) below room
temperature.
Conventional systems: heating should shut off and fan
should shut off after a short delay.
Heat pump systems: heating and fan should shut off.
NOTE: Some electric heat systems require control of fan
operation from the thermostat. These systems
require a thermostat with control of fan operation
in response to a call for heating or cooling.
Cooling
CAUTION
Damage to Compressor Possible.
Operating at too low of an outdoor temperature
may cause compressor damage.
Do not operate cooling if outdoor temperature is
below 50°F (10°C). Refer to manufacturer recommendations.
NOTE: To prevent compressor short cycling, a minimum
off-timer may be included to provide a five-minute
time delay before activating the compressor after
the thermostat last turned off the compressor, or
after the system first received power. This delay
protects the compressor.
With the system switch set at COOL and fan switch, if
applicable, at AUTO, move the temperature setting lever
about 10°F (6°C) below room temperature. Cooling and
fan should start (see NOTE above). Move the temperature
setting lever about 10°F (6°C) above room temperature.
Cooling and fan should shut off.
Fan
T834B
Fan operates with the cooling equipment in cooling; fan
operates in response to the plenum fan control in heating.
T834C
With the system switch set at OFF, and the fan switch at
ON, the fan should run continuously. Move the fan switch
to AUTO. In conventional systems, fan operation is
controlled by the thermostat in cooling and by the plenum
fan control in heating. In heat pump systems, fan operation
is controlled by the thermostat in both heating and cooling.
T834J
With the system switch set at OFF, and the fan switch
at ON, the fan should run continuously. Move the fan
switch to AUTO. The fan operation is controlled by the
thermostat.
7
69-0444—10
Page 8
T834B; T834C; T834J HEATING-COOLING THERMOSTATS
RECALIBRATION
These thermostats are calibrated at the factory and should
not need recalibration. If the thermostat seems out of
adjustment, first check for accurate leveling. To check
calibration, proceed as follows:
1. Move the temperature setting lever to the left
(low) end of the temperature scale. Place system
switch at OFF. Wait at least five minutes.
2. Remove the thermostat cover. Move the setting
lever until the switch just makes contact. The
mercury in the switch will roll to the left end of
the tube.
3. Replace cover and wait five minutes for the cover
and the thermostat to lose the heat it has gained
from your hands. If the thermometer pointer and
the setting lever indicator read approximately the
same, no recalibration is needed.
If recalibration appears necessary, proceed as follows:
1. Place the temperature setting lever at the same
setting as the thermometer. Remove cover.
2. Insert Honeywell part no. 104994A Calibration
Wrench (order separately) onto the hex nut under
the coil. See Fig. 13. Holding the setting lever so
it does not move, turn the wrench clockwise
until the mercury rolls to the right end of the tube.
Remove wrench and replace cover.
To ensure accurate temperature control, do not
touch or breathe on bimetal or thermometer.
3. Move the setting lever to a low setting. Wait at
4. Slowly move the setting lever until it reads the
5. Remove cover. Holding the setting lever so it
6. Recheck calibration. Set thermostat system
least five minutes for temperature to stabilize.
same as the thermometer.
does not move, reinsert wrench and carefully turn
counterclockwise until the mercury rolls to
the left end of the tube but no farther.
switch for desired operation and replace cover.
COIL SHOWN WITHOUT
HEAT ANTICIPATOR
CALIBRATION
WRENCH
M2044A
Fig. 13. Recalibration procedure.
Automation and Control Solutions
Honeywell International Inc. Honeywell Limited—Honeywell Limitée
1985 Douglas Drive North 35 Dynamic Drive
Golden Valley, MN 55422 Scarborough, Ontario M1V 4Z9
69-0444—10 8
69-0444—10 G.H. Rev. 5-99
www.honeywell.com/yourhome
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