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TRADELINE  
T834C  
Heating-Cooling Thermostat  
Application  
T834C Thermostats control 24 to 30 Vac single-stage heating-cooling systems. See Table 1 for specific models and  
applications.AnspdtmercuryswitchmakesRtoWonatemperaturefallforheating,andRtoYonatemperatureriseforcooling.  
See Fig. 1.  
TABLE 1—THERMOSTAT MODELS AND APPLICATIONS.  
Heat  
Anticipator  
Range  
Model  
Number  
Switching  
System  
See  
Fig.  
Application  
Fan  
Comments  
T834C1137 For use in standard  
heating-cooling  
HEAT-OFF- ON-AUTO 0.18 to 1.0A TRADELINE; Beige.  
COOL  
3
4
5
systems.  
T834C1541 For use in gas- or  
oil-fired, or central  
SUPER TRADELINE;  
Beige.  
a
electric heat systems.  
T834C2267 For use in gas- or  
oil-fired, single-stage  
SUPER TRADELINE;  
Premier White.  
(Jumper included.)  
heat pump or central  
a
electric heat systems.  
T834C2309 For use in standard  
heating-cooling  
0.3 to 1.2A TRADELINE; Beige.  
3
systems.  
aIn electric heat applications without fan sequencers, jumper terminals 1 and 2 to control the fan from the thermostat during  
heating.  
Contact your local waste management authority for in-  
Fig. 1—Internal view of T834C.  
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 Inc. at 1-800-468-  
502.  
1
Installation  
WHEN INSTALLING THIS PRODUCT...  
. Read these instructions carefully. Failure to follow  
1
them could damage the product or cause a hazardous condi-  
tion.  
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 op-  
eration as provided in these Instructions.  
CAUTION  
Recycling Notice  
M3375  
Disconnect power supply before beginning instal-  
lation to prevent electrical shock or equipment  
damage.  
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.  
J. H. • Rev. 2-93 •  
• ©Honeywell Inc. 1993 • Form Number 69-0434—5  
M3375  
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LOCATION  
Locate the thermostat about 5 ft. [1.5 m] above the floor  
on an inside wall in an area with good air circulation at  
average temperature.  
Fig. 2—Jumpering thermostat terminals to control  
fan operation.  
Do not mount the thermostat where it can 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.  
unheated(uncooled)areasbehindthethermostat, such  
as outside walls.  
This thermostat is a precision instrument and was care-  
fully adjusted at the factory. Handle it carefully.  
MOUNTING AND WIRING  
Disconnectpowersupplybeforebeginninginstallationto  
prevent electrical shock or equipment damage.  
All wiring must comply with local codes and ordinances.  
The T834C can be mounted directly to a wall or vertical  
outlet box. Use Honeywell part no. 193121A (beige) or  
2
02689A (gray) Mounting Plate Assembly (order sepa-  
rately) to mount on horizontal outlet box or cover marks left  
byoldthermostat.Ifmountingplateassemblyisused,review  
instructionsprovidedwithassemblybeforewiringandmount-  
ing thermostat. To wire and mount thermostat:  
1. In replacement applications, check the existing ther-  
mostat wires for cracked or frayed insulation. Replace any  
wires in poor condition. If the wire is plastered into the wall,  
makeaholenexttothewiresandloosenthewiressothatthey  
can be pushed back into the wall later.  
5
. Remove thermostat cover by pulling outward on bot-  
tom edge until it snaps free of the thermostat base. Carefully  
remove and discard the foam plastic shipping insert. This  
insert protects the switch and bimetal assembly during ship-  
ping.  
2
. In new installations, run wiring (if necessary) to the  
thermostat location.  
. Set the adjustable heat anticipator indicator to match  
3
the current draw of the primary heating control or as recom-  
mended by the equipment manufacturer (see Heat Anticipa-  
tor Setting).  
6. Push excess wire back through the hole and plug any  
opening with insulation to prevent drafts that may affect  
thermostat performance.  
4. Connect the wires to the terminals on the back of the  
7. Fasten the thermostat to the wall or outlet box with a  
thermostat. See Figs. 3-5 for internal schematic and typical  
hookup diagrams. If using electric heat-compatible thermo-  
stat in central electric heat applications, jumper terminals 1  
and 2 to control fan operation from the thermostat during  
heating. See Fig. 2.  
screw through the top mounting hole. Adjust the thermostat  
so that it is approximately level and fasten the second screw  
through the bottom mounting hole. Do not tighten.  
8. Exactly level the thermostat using a spirit level or  
plumb line. Tighten the mounting screws.  
Fig. 3—Internal schematic and typical hookup for T834C1137 and T834C2308 in a standard heating-cooling  
system.  
L1  
(HOT)  
R
FAN SWITCH  
FAN RELAY  
L2  
ON  
1
H1  
G
Y
C1  
AUTO  
C1  
COMPRESSOR  
CONTACTOR  
TEMP. FALL  
ANTICIPATOR  
SYSTEM  
SWITCH  
H1  
ANTICIPATOR  
COOL  
HEAT  
OFF  
OFF  
HEAT  
COOL  
HEAT RELAY  
W
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
M1119A  
2
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Fig. 4—Internal schematic and typical hookup for T834C1541 in gas- or oil-fired, or central electric heat system.  
1
L1  
R
(HOT)  
L2  
FAN  
SWITCH  
FAN RELAY  
ON  
H1  
TEMP. FALL  
G
1
C1  
AUTO  
COMPRESSOR  
CONTACTOR  
2
C1  
H1  
ANTICIPATOR  
ANTICIPATOR  
Y
2
SYSTEM  
SWITCH  
COOL  
OFF  
HEAT  
OFF  
HEAT  
COOL  
HEAT RELAY  
W
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
IN ELECTRIC HEAT OR SINGLE-STAGE HEAT PUMP APPLICATION, JUMPER 1 AND 2 FOR AUTO FAN IN HEATING AND COOLING.  
M2690  
Fig. 5—Internal schematic and typical hookup for T834C2267 in gas- or oil-fired, single-stage heat pump or  
central electric heat system.  
1
FAN RELAY  
FAN  
G
SWITCH  
AUTO  
1
ON  
L1  
R
(HOT)  
L2  
CHANGEOVER  
RELAY (COOL)  
H1  
TEMP. FALL  
C1  
O
2
2
C1  
H1  
ANTICIPATOR  
ANTICIPATOR  
SYSTEM  
SWITCH  
HEAT RELAY  
W
COOL  
OFF  
HEAT  
OFF  
COMPRESSOR  
RELAY  
4
3
HEAT  
COOL  
Y
CHANGEOVER  
RELAY (HEAT)  
B
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.  
JUMPER 1-2 FOR AUTO FAN IN HEATING AND COOLING (ELECTRIC HEAT AND SINGLE STAGE HEAT PUMP SYSTEMS).  
JUMPER 1-Y FOR AUTO FAN IN COOLING ONLY.  
2
3
4
JUMPER W-Y FOR SINGLE-STAGE HEAT PUMP APPLICATIONS.  
M2323B  
3
69-0434—5  
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9
. Adjust temperature setting lever so mercury bulb is in  
horizontal position. See Fig. 1.  
0. Carefully replace thermostat cover.  
8. With the system operating through the ammeter, wait  
one minute, then read the ammeter.  
1
9. Turn the system switch to OFF, and turn off power.  
10. Adjust the heat anticipator to match the reading on the  
IMPORTANT:Anincorrectlyleveledthermostatwillcause  
ammeter.  
the temperature control to deviate from setpoint.  
11. Disconnect the ammeter, reconnect the W wire, and  
mount the thermostat. Continue with system checkout.  
NOTE: The heat anticipator may require further adjustment  
for best performance. To lengthen burner-on time, move  
the indicator in the direction of the longer arrows—not  
more than a half scale marking at a time. To shorten  
burner-on time, move indicator in opposite direction.  
Setting and Adjustment  
TEMPERATURE SETTING  
Push the temperature setting lever to the desired control  
point on the temperature scale. The same lever controls both  
heating and cooling.  
HEAT ANTICIPATOR SETTINGS (Fig. 4 only)  
Heat Pump Systems (for about 3 cycles per hour)  
Using ‘B’ Terminal  
Set adjustable anticipator to 140 percent of combined  
current draw of compressor and fan relays.  
SYSTEM AND FAN SWITCHING  
The T834C features SYSTEM and FAN switches for  
control of the heating-cooling and fan systems.  
The SYSTEM switch controls system operation as fol-  
lows:  
Using ‘O’ Terminal  
Setadjustableanticipatortomaximumscalesetting.Limit  
combined load current of compressor and fan relays to 0.8  
amp, because cooling anticipator provides anticipation dur-  
ing heat cycle in this hookup.  
HEAT: Heating system only operates.  
OFF: Both heating and cooling control systems are dis-  
connected.  
COOL: Cooling system only operates.  
Electric Systems (with auto fan in heating and cooling)  
Set adjustable anticipator to combined current draw of  
heating and fan relays.  
The FAN switch controls fan operation as follows:  
AUTO: For gas- or oil-fired systems, the fan operates in  
response to the thermostat in cooling; fan operates in  
response to the plenum fan control in heating. For  
single-stage heat pump and electric heat systems, the  
fan operates in response to the thermostat in both  
heating and cooling.  
Gas- and Oil- Fired Systems  
(
without auto fan in heating)  
Set adjustable anticipator to current draw of heat relay or  
valve.  
ON: The fan runs continuously.  
To switch positions, use thumb and index finger to slide  
levertodesiredposition. Switchlevermuststopdirectlyover  
desired function indicator mark for proper circuit operation.  
HEAT ANTICIPATOR SETTING  
Checkout  
IMPORTANT: The T834C Thermostat has an adjustable  
heat anticipator and equipment will cycle properly  
ONLY IF THE ANTICIPATOR IS ADJUSTED TO  
MATCH THE CURRENT DRAW OF THE ENTIRE  
SYSTEM or as recommended by the equipment  
manufacturer. 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  
CAUTION  
Do not check operation by shorting across termi-  
nals of system controls. This will damage the heat  
anticipator.  
(millivolt) Systems.  
IMPORTANT:Toassureaccuratetemperaturecontrol,do  
not touch or breathe on bimetal of thermometer.  
Acurrentratingisusuallystampedinthenameplateofthe  
primary control. Set the adjustable heat anticipator indicator  
tomatchthevaluegivenonthenameplate,exceptonthermo-  
stats used in systems as shown in Figs. 2-4. See Heat  
Anticipator Settings (Figs. 2-4).  
If current rating is not available, proceed as follows to  
determine the rating:  
HEATING  
WithsystemswitchsetatHEATandfanswitchatAUTO,  
move the temperature setting lever about 10° F  
[
6° C] above room temperature.  
Gas- or oil-fired systems—heating should start; fan  
should start after a short delay.  
1
2
3
. Turn off power.  
. Wire thermostat, but do not mount it on the wall.  
. Connect ammeter between W wire and W terminal on  
Single-stage heat pump or central electric heat sys-  
tems—both heating and fan should start immediately.  
Move temperature setting lever 10° F [6° C] below room  
temperature.  
Gas- or oil-fired systems—heating should shut off and  
fan should shut off after a short delay.  
the thermostat.  
4
5
6
7
. Prepare the system for operation.  
. Turn on power.  
. Turn system switch to heat.  
. Increasethermostatsetpointasnecessarytogetsystem  
Single-stage heat pump or central electric heat sys-  
tems—heating and fan should shut off immediately.  
operating.  
4
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COOLING  
If recalibration appears necessary, proceed as  
follows:  
1
. Place the temperature setting lever at the same setting  
CAUTION  
as the thermometer. Remove cover.  
Do not operate cooling if outdoor temperature is  
below 50° F [10° C]. Refer to manufacturer’s  
recommendations.  
2. Insert104994ACalibrationWrench(orderseparately)  
ontothehexnutunderthecoil. SeeFig. 6. Holdingthesetting  
leversoitdoesnotmove,turnthewrenchclockwise  
until  
the mercury drops 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 least  
five minutes for temperature to stabilize.  
4. Slowly move the setting lever until it reads the same as  
the thermometer.  
NOTE:Topreventcompressorshortcycling,somemanufac-  
turers’ equipment includes a minimum off-timer to pro-  
vide a five-minute time delay before activating the com-  
pressor when the thermostat last turned the compressor  
off, or from when the system first received power. This  
delay protects the compressor.  
WiththesystemswitchsetatCOOLandthefanswitch set  
at AUTO, move the temperature setting lever about  
5. Remove cover. Holding the setting lever so it does not  
move, reinsert wrench and carefully turn  
1
0°F[6°C]belowroomtemperature.Coolingandfanshould  
counterclockwise  
untilthemercurydropstotheleft  
start (see NOTE above). Move the temperature setting lever  
about 10°F [6°C] above room temperature. Cooling and fan  
should shut off.  
of the tube, but no farther.  
6. Recheck calibration. Set the thermostat system switch  
for desired operation and replace cover.  
7. Adjust temperature setting lever so mercury bulb is in  
FAN  
position. See Fig. 1  
8. Carefully replace thermostat cover.  
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 gas- or oil-fired systems, fan operation is con-  
trolled by the thermostat in cooling and by the plenum fan  
control in heating. In single-stage heat pump and central  
electric heat systems, fan operation is controlled by the  
thermostat in both heating and cooling.  
Fig. 6—Recalibration procedure.  
RECALIBRATION  
These thermostats are calibrated at the factory and should  
not need recalibration. If the thermostat seems out of adjust-  
ment, first check for accurate leveling. To check calibration,  
proceed as follows.  
COIL SHOWN WITHOUT  
HEAT ANTICIPATOR  
1. Move the temperature setting lever to the left end (low  
end) of the temperature scale. System switch must be placed  
at OFF. Wait at least five minutes.  
2. Remove the thermostat cover. Move the setting lever  
untiltheswitchjustmakescontact.Themercuryintheswitch  
will drop to the left end of the tube.  
CALIBRATION  
3
. Replace cover and wait five minutes for the cover  
WRENCH  
M2044  
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.  
5
69-0434—5  
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Automation and Control Solutions  
Honeywell Internationals Inc.  
Honeywell Limited—Honeywell Limitée  
35 Dynamic Drive  
1
985 Douglas Drive North  
Golden Valley, Minnesota 55422  
Scarborough, Ontario M1V 4Z9