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T8034C Heating and  
Cooling Thermostat  
INSTALLATION INSTRUCTIONS  
APPLICATION  
The T8034C Thermostat (see Fig. 1) controls 24 to 30 Vac single-stage heating-cooling systems. See Table 1 for  
application information. An spdt mercury switch makes R to W on a temperature fall for heating, and R to Y on a  
temperature rise for cooling.  
Table 1. T8034C Specifications.  
Switching  
Heat  
See Fig.  
No.  
Model No.  
Application  
Anticipation  
System  
Fan  
Comments  
T8034C1085  
For use in gas- or  
oil-fired heating  
systems.  
0.18A to 1.0A,  
adjustable.  
Heat-Off-  
Cool  
On-Auto  
TRADELINE®  
3
MOUNTING HOLE  
BIMETAL ELEMENT  
BEHIND HEAT  
ANTICIPATOR  
(THERMOSTAT  
MERCURY NOTICE  
TO WALL OR  
OUTLET BOX)  
SYSTEM  
SWITCH  
MOUNTING  
HOLE  
If this control is replacing a control that contains  
mercury in a sealed tube, do not place your old  
control in the trash. Dispose of properly.  
SCALE  
Contact your local waste management authority  
for instructions regarding recycling and the  
proper disposal of an old control.  
.
18  
.9  
.7  
.
2
.
5
.
25  
.
3
.35  
INSTALLATION  
When Installing This Product . . .  
1
.
Read these instructions carefully. Failure to follow  
them could damage the product or cause a hazard-  
ous condition.  
Check the ratings given in the instructions and on  
the product to make sure the product is suitable for  
your application.  
Installer must be a trained, experienced service  
technician.  
After installation is complete, check out the product  
operation as provided in these instructions.  
FAN  
SWITCH  
TEMPERATURE  
SETTING LEVER  
M5601  
ADJUSTABLE HEAT  
ANTICIPATOR INDICATOR  
2.  
Fig. 1. T8034C internal view.  
3
.
.
4
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U.S. Registered Trademark  
Copyright © 2001 Honeywell •  
• All Rights Reserved  
69-1596  
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T8034C HEATING AND COOLING THERMOSTAT  
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.  
In new installations, run wiring (if necessary) to the  
thermostat location.  
Connect the wires to the terminals on the back of  
the thermostat. See Fig. 3 for internal schematic  
and typical hookup diagram.  
Remove thermostat cover by pulling outward on  
right edge of cover until it snaps free of the thermo-  
stat base. Carefully remove and discard the foam  
plastic shipping insert that protects the switch and  
bimetal assembly during shipping.  
Set the adjustable heat anticipator indicator to  
match the current draw of the primary heating con-  
trol (see Heat Anticipator Setting section).  
Push excess wire back through the hole and plug  
any opening with insulation to prevent drafts that  
can affect thermostat performance.  
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.  
2
.
.
3
Do not mount the thermostat where it can be affected by:  
—
—
—
—
drafts or dead spots behind doors or in corner.  
hot or cold air from ducts.  
radiant heat from the sun, fireplaces or appliances.  
unheated (uncooled) areas such as outside walls  
behind the thermostats.  
4.  
This thermostat is a precision instrument and was  
carefully adjusted at the factory. Handle it carefully.  
5
.
.
Wiring and Mounting  
6
CAUTION  
7. Loosely fasten the thermostat (with wallplate, if  
applicable) to the wall or outlet box with a screw  
through the left mounting hole. Adjust the thermo-  
stat so it is approximately level and fasten the sec-  
ond screw through the right mounting hole. Do not  
tighten.  
Electrical Shock Hazard.  
Can cause personal electrical shock and  
equipment damage.  
Disconnect power supply before beginning  
installation.  
8.  
For optimum performance, level the thermostat  
using a spirit level or plumb line. Tighten the  
mounting screws.  
IMPORTANT  
All wiring must comply with local codes and  
ordinances.  
9.  
Adjust temperature setting lever so mercury bulb is  
in horizontal position as shown in Fig. 2.  
1
0. Carefully replace the thermostat cover.  
The T8034C can be mounted directly on a wall or  
horizontal outlet box:  
Use the 200581 (beige) or 202895A (gray) Horizontal  
Wallplate to cover mounting marks from an old  
thermostat.  
Use the 19312A (beige) or 202689A (gray) Mounting  
Plate Assembly to mount on vertical outlet box or to  
cover wall marks where larger plate is needed.  
IMPORTANT  
—
An incorrectly leveled thermostat causes the  
temperature control to deviate from setpoint.  
—
The SUPER TRADELINE® T8034C includes the 200581  
Horizontal Wallplate. For other T8043C models, order the  
horizontal wallplate or mounting plate assembly.  
UP  
If the horizontal wallplate is used, align the thermostat  
and wallplate. See Fig. 2. Press firmly together until  
wallplate snaps in place, then wire and mount the  
thermostat.  
Cool  
Off  
Heat  
If the mounting plate assembly is used, review the  
instructions provided with the assembly before wiring and  
mounting the thermostat.  
9
0
8
0
70  
60  
To wire and mount the thermostat:  
Auto  
1.  
In replacement applications, check the existing  
thermostat wires for cracked or frayed insulation.  
Replace any wires in poor condition. If the wire is  
FAN  
On  
M20287  
Fig. 2. Mounting T8034C Thermostat on wallplate.  
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T8034C HEATING AND COOLING THERMOSTAT  
L1  
(HOT)  
RC  
FAN SWITCH  
FAN RELAY  
L2  
H1  
C1  
ON  
G
Y
1
TEMP. FALL  
H1  
AUTO  
ANTICIPATOR  
COOL RELAY  
C1  
2
ANTICIPATOR  
SYSTEM  
SWITCH  
COOL  
RH  
HEAT  
OFF  
OFF  
1
HEAT  
COOL  
HEAT RELAY  
L1  
(
HOT)  
1
2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND  
OVERLOAD PROTECTION AS REQUIRED.  
W
L2  
M2043C  
IN SINGLE TRANSFORMER SYSTEMS, JUMP RC AND RH.  
Fig. 3. Internal schematic and typical hookup for T8034C1085 in dual-transformer heating-cooling systems.  
Look for the current rating stamped on the nameplate of  
SETTINGS AND ADJUSTMENTS  
the primary control. Set the adjustable heat anticipator  
indicator to match the value shown on the nameplate.  
Temperature Setting  
If the current rating is not available, proceed as follows to  
Push the temperature setting lever to the desired control  
point on the temperature scale. The same lever controls  
the temperature setting for either heating or cooling.  
determine the rating:  
1. Turn off the power.  
2
.
Wire the thermostat, but do not mount it on the  
wall.  
Connect the ammeter between the W wire and the  
W terminal on the thermostat (in series with the pri-  
mary control).  
3.  
System and Fan Switching  
The T8034C has System and Fan switches to control the  
heating-cooling systems and fan.  
4. Prepare the system for operation.  
Turn on the power.  
6. Turn the System switch to Heat.  
5.  
The System switch controls system operation:  
Heat: Operates only heating system.  
Off: Both heating and cooling systems are discon-  
nected.  
7
8
9
.
.
.
Increase the thermostat setpoint, as necessary, to  
begin operating the system.  
With the system operating through the ammeter,  
wait one minute, then read the ammeter.  
Turn the System switch to Off and turn off the  
power.  
Cool: Operates only cooling system.  
The Fan switch controls fan operation:  
Auto: For gas-or oil-fired systems; the fan operates in  
response to the thermostat in cooling and in  
response to the plenum fan control in heating. For  
electric heat or heat pump systems, the fan oper-  
ates in response to the thermostat in both heating  
and cooling.  
1
0. Adjust the heat anticipator to match the ammeter  
reading.  
1. Disconnect the ammeter, reconnect the W wire,  
and mount the thermostat.  
1
NOTE: For best performance, the heat anticipator may  
require further adjustment. To lengthen burner-  
on time, move the indicator in the direction of  
the longer arrows but not more than one-half  
scale marking at one time. To shorten burner-on  
time, move the indicator in the opposite direc-  
tion.  
On: The fan runs continuously.  
To switch positions, use thumb and index finger to slide  
lever to desired position. Stop switch lever in detent  
directly over desired position. Stop switch lever in detent  
directly over desired function indicator mark for correct  
circuit operation.  
CHECKOUT  
Heat Anticipator Setting  
IMPORTANT  
The T8034C Thermostat has an adjustable heat  
anticipator and operates correctly only if the  
anticipator is adjusted to match the current draw  
of the primary control. Use this thermostat only  
on systems with current draw that falls within  
the range of the heat anticipator. Do not use this  
device on Powerpile® Systems (millivolt).  
CAUTION  
Equipment Damage Hazard.  
Heat anticipator can be damaged.  
Do not check operation by shorting across  
system control terminals.  
IMPORTANT  
To assure accurate temperature control, do not  
touch or breathe on bimetal or thermometer.  
3
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T8034C HEATING AND COOLING THERMOSTAT  
To check calibration:  
Heating  
1.  
Move the temperature setting lever to the lower  
end of the temperature scale. Place the System  
switch to the Off position. Wait at least five min-  
utes.  
With System switch set at Heat, and Fan switch set at  
Auto, 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.  
2
.
.
Remove the thermostat cover. Move the setting  
lever until the switch just makes contact. (The mer-  
cury in the switch rolls to the left end of the tube.)  
Replace the 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.  
Central electric heat or heat pump systems: both  
heating and fan should start.  
Move the temperature setting lever about 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.  
Electric heat or heat pump systems: heating and fan  
should shut off.  
3
If recalibration appears necessary:  
1.  
Place the temperature setting lever at the same  
setting as the thermometer. Remove the cover by  
pulling out on the right edge of the cover until it  
snaps free of the thermostat base.  
Cooling  
CAUTION  
Air conditioning equipment (compressor) can  
be damaged.  
Do not operate cooling when outdoor  
temperature is below 50°F (10°C). Refer to  
manufacturer’s recommendations.  
2. Insert the 104994A Calibration Wrench (ordered  
separately) onto the hex nut under the coil. (See  
Fig. 4.) 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 the  
wrench and replace the cover.  
Equipment Damage Hazard.  
IMPORTANT  
To assure accurate temperature control, do not  
touch or breathe on bimetal or thermometer.  
IMPORTANT  
To prevent compressor short cycling, some  
manufacturer’s equipment includes a minimum-  
off timer to provide a five-minute time delay  
from when the thermostat last turned off the  
compressor, or from when the system first  
received power. This delay protects the com-  
pressor.  
3
4
5
.
.
.
Move the setting lever to a lower setting. Wait at  
least five minutes for the temperature to stabilize.  
Slowly move the setting lever until it reads the  
same as the thermometer.  
Remove the cover. Holding the setting lever so it  
does not move, reinsert the wrench and carefully  
turn it counterclockwise just until the mercury rolls  
to the left end of the tube but no farther.  
WIth the System switch set at Cool and the Fan switch  
set to Auto, move the temperature setting lever about  
0°F (6°C) below room temperature. Cooling and fan  
should start (see Important above). Move the  
temperature setting lever about 10°F (6°C) above room  
temperature. Cooling and fan should shut off.  
6.  
7.  
8.  
Recheck the calibration. Set the thermostat Sys-  
tem switch for the desired operation.  
1
Adjust the temperature setting lever so the mercury  
bulb is in position as shown in Fig. 4.  
Carefully replace the thermostat cover.  
Fan  
With the System switch set to Off and the Fan switch set  
to On, the fan should run continuously. Move the Fan  
switch to Auto. In gas- or oil-fired systems, fan operation  
is controlled by the plenum fan control in heating and by  
the thermostat in cooling. In central electric heat and heat  
pump systems, fan operation is controlled by the  
thermostat in both heating and cooling.  
COIL SHOWN WITHOUT  
HEAT ANTICIPATOR  
CALIBRATION  
WRENCH  
M2044A  
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.  
Fig. 4. Recalibrating the thermostat.  
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