Honeywell TRADELINE T8400C User manual

APPLICATION
The T8400C Thermostat provides single-stage, non-
programmable temperature control for 24 Vac heating-
cooling systems with manual changeover from heat to
cool. Heating cycle rate is selectable at 1, 3, 4, 5, 6, 9, or
12 cph. Cooling cycle rate is fixed at 3 cph. Temperature
indication can be set for °F or °C.
The T8400C Thermostat is powered through the heating
and/or cooling system controls.
T8400C includes a thermostat, wallplate (for wiring and
mounting thermostat) and Owner’s Guide.
MERCURY NOTICE
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.
Contact your local waste management authority
for instructions regarding recycling and the
proper disposal of an old control.
X-XX UL
INSTALLATION INSTRUCTIONS
®U.S. Registered Trademark
Copyright © 2002 Honeywell • • All Rights Reserved
T8400C
Electronic Thermostat
INSTALLATION
When Installing this Product…
1. Read these instructions carefully. Failure to follow
them could damage the product or cause a hazard-
ous 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
Equipment Damage Hazard.
Can short equipment circuitry.
Disconnect power supply before installation.
Location
Install the thermostat about 5 ft (1.5m) above the floor in
an area with good air circulation at average temperature.
See Fig. 1. Do not install the thermostat where it can be
affected by:
—drafts or dead spots behind doors and in corners.
—hot or cold air from ducts.
—radiant heat from the sun or appliances.
—concealed pipes and chimneys.
—unheated (uncooled) areas such as an outside wall
behind the thermostat.
This thermostat is a precision instrument and was carefully
adjusted at the factory.
Handle it carefully.
69-1493-1

69-1493–1 2
T8400CELECTRONICTHERMOSTAT
Setting Fan Operation (Fuel) Switch
The fan operation (fuel) switch is preset at the factory in
the F position. See Fig. 3. This is the correct setting for
most systems. If this system is an electric heat system, set
the switch to the E position. The E setting allows the fan to
turn on immediately with the heating or cooling equipment
in a system where the G terminal is connected.
Fig. 1. Typical location of thermostat.
Mounting Wallplate to Wall
IMPORTANT
Level only for appearance. The thermostat
functions normally even when not level.
Mount wallplate with the screws provided (see Fig. 2) as
follows:
1. Place the wallplate at the desired location on the
wall.
2. Pull the thermostat wire through the wallplate
entrance hole.
3. Select the two mounting holes that best fit the
application.
4. Fasten the wallplate to the wall using the anchors
and screws provided.
5. After wiring the wallplate, plug the hole to prevent
drafts from affecting the thermostat.
Fig. 2. Mounting wallplate to wall.
5 FEET
[1.5 METERS]
YES
NO
NO
NO
M11338
M12202A
WALL WALL
ANCHORS (2)
WALLPLATE
WHEN USING WALL ANCHORS, DRILL 3/16 INCH
HOLES FOR DRYWALL, 7/32 INCH HOLES FOR
PLASTER OR WOOD.
MOUNTING
SCREWS (2)
1
1
M1258
0
FAN OPERATION (FUEL) SWITCH
F
E
Fig. 3. Fan operation (fuel) switch.

69-1493–1
3
T8400C ELECTRONIC THERMOSTAT
TERMINAL
SCREW
M13274
G
Rc
R
Y
WB
O
FOR STRAIGHT INSERTION
STRIP 5/16 IN. (8 MM)
FOR WRAPAROUND
STRIP 7/16 IN. (11 MM
)
L1
(HOT)
L2
1
1
COOLING
CONTACTOR
FAN
RELAY
HEATING
PRIMARY
CONTROL
24V
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
FACTORY INSTALLED JUMPER.
M13275
Y
G
Rc
W
RB
O
2
2
KEEP WIRING IN
SHADED AREA
MOUNTING
SCREW HOLE MOUNTING SCREW HOLE
WIRING ENTRANCE
HOLE
M16432
G
Rc
R
Y
WB
O
Wiring
IMPORTANT
Use an 18-gauge maximum wire for wiring the
T8400C Thermostat.
All wiring must comply with local electrical codes and
ordinances. Disconnect the power supply to prevent
electrical shock or equipment damage.
NOTE: To ensure proper mounting of thermostat, restrict
all wiring to the shaded area. See Fig. 4.
The shape of the terminals permits insertion of straight or
wraparound wiring connections; either method is accept-
able. See Fig. 5.
Fig. 4. Restrict wiring to shaded area.
Fig. 5. Wiring connections.
The T8400C Thermostat is powered through the heating/
cooling system controls and is adaptable to most 4-wire,
24 Vac heating-cooling systems.
Refer to Fig. 6, 7, and 8 for typical wiring hookups.
Fig. 6. Typical hookup of T8400C in heat-cool system
with single transformers.

69-1493–1 4
T8400CELECTRONICTHERMOSTAT
Mounting Thermostat to Wallplate
1. Engage the tabs at the top of the thermostat and
wallplate.
2. Swing down the thermostat and press the lower
edge of the thermostat onto the wallplate to latch.
See Fig. 9.
Fig. 7. Typical hookup of T8400C in heat-cool system
with two transformers.
Fig. 8. T8400C in one-stage heat, one-stage cool
wiring diagram with manual changeover.
Y
G
Rc
W
24
R
B
O
M12562
L1
(HOT
)
L2
FAN
RELAY
HEAT
RELAY
L1
(HOT)
L2
COMPRESSOR
CONTACTOR
HEATING
TRANSFORMER
COOLING
TRANSFORMER
HEAT
DAMPER
COOL
DAMPER
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
REMOVE RC TO R JUMPER WHEN INSTALLED ON A TWO TRANSFORMER
SYSTEM.
CAN BE USED FOR CHANGEOVER VALVE ON SINGLE-STAGE HEAT
PUMP SYSTEMS.
POWER TO R TERMINAL IS REQUIRED WHEN THE SYSTEM SWITCH IS IN
THE OFF POSITION.
2
3
3
1
1
3
4
Fig. 9. Mounting thermostat to wallplate.
L
1
(
HOT)
L
2
1
COOL
CHANGEOVER
FAN
RELAY
COOL
RELAY
HEAT
RELAY
24V
M13277
A
HEAT
CHANGEOVER
TRANSFORMER
1POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
CAN BE USED FOR CHANGEOVER VALVE ON
SINGLE-STAGE HEAT PUMP SYSTEMS.
FACTORY INSTALLED JUMPER.
2
3
2
2
Y
G
Rc
W
R
B
O
3
M14677A
SYSTEM
Cool Off Heat
Auto On
FAN
DASHED LINES INDICATE TABS
ON BACK OFTHERMOSTAT
SYSTEM
Cool Off Heat
Auto On
FAN
ENGAGE TABS AT TOP OF THERMOSTAT
WITH SLOTS ON MOUNTING PLATE.
PRESS LOWER EDGE OF
CASE TO LATCH.
A
B
Set Room
Set Room

69-1493–1
5
T8400C ELECTRONIC THERMOSTAT
OPERATION
Setting FAN and SYSTEM Switches
Fan and system settings are controlled manually by using
the switches located at the bottom of the thermostat case.
See Fig. 10.
Fig. 10. Digital display and
Fan and System switches.
FAN Switch
Fan switch settings are:
Auto: Normal setting for most homes. In cooling, the
fan starts and stops with the cooling equipment. In
heating, the fan is controlled directly by the heating
equipment and may start a few minutes after the
heating equipment turns on (for most systems).
When using an electric heat thermostat, the fan
starts and stops with the heating equipment.
On: The fan runs continuously. Use for improved air
circulation and air quality.
Slide the FAN switch in the bottom left corner of the
thermostat to select the desired fan setting.
SYSTEM Switch
System switch settings control thermostat operation as
follows:
Cool: The thermostat controls the cooling system.
Off: Both heating and cooling are off.
Heat: The thermostat controls the heating system.
Slide the SYSTEM switch in the bottom right corner of the
thermostat to select the desired system setting.
Set Temperature Setpoint
NOTE: Temperature setpoint range is 40°to 99°F (5°to
37°C).
The temperature setpoint and the room temperature are
shown separately on the digital display. The ▼ indicator
points to Set when the temperature setpoint is displayed
and to Room when the room temperature is displayed.
To set temperature setpoint:
1. Select Heat or Cool by sliding the SYSTEM switch in
the lower right corner of the thermostat to the
desired mode. See Fig. 10.
2. To display the temperature setpoints on the digital
display, press either the ▲ or ▼ key once. The
temperature setpoint is displayed for approximately
five seconds as the indicator points to Set and
flashes.
3. To increase the temperature setpoint, press the ▲
key. Each press changes the setpoint one degree;
press and hold to change the setpoint several
degrees.
4. To decrease the temperature setpoint, press the ▼
key. Each press changes the setpoint one degree;
press and hold to change the setpoint several
degrees.
Setting ° F/ ° C Indication and Heat Cycle Rate
NOTE: To save changes to the °F/°C indication and
the heat cycle rate, all seven steps must be
completed.
To set the °F/°C indication and heat cycle rate:
1. If the temperature is displayed in °F, set the
temperature setpoint to 52°F. If the room tempera-
ture is displayed in °C, set the temperature setpoint
to 11°C.
M1468
2
M1468
3
SYSTEM
Cool Off Heat
Auto On
FAN
M14678A
TEMPERATURE DISPLAY
INCREASE SETTING
DECREASE SETTING
FAN SWITCH
SYSTEM SWITCH
Set Room
S
et Room
INDICATOR
ROOM TEMPERATURE
SETPOINT TEMPERATURE
M1467
9
M1468
0
M1468
1

69-1493–1 6
T8400CELECTRONICTHERMOSTAT
Table 1. Heating Cycle Rates.
Optional System Checkout
When in steps 2and 3only, the ▼key can be
used to turn heat or cool outputs on and off.
Change the SYSTEM switch setting to test heat
or cool outputs. No action takes place if the
SYSTEM switch is in the Off position.
Examples: System setting at HEAT: If heat is
on, the ▼ key turns it off; if heat is
off, ▼turns it on.
System setting at COOL: If cool is
on, ▼key turns it off; if cool is off,
▼turns it on.
2. Press the ▲▼ keys simultaneously for more than
one second to light all segments on display and to
enter installer setup mode. When the keys are
released, a two-digit software revision code is
displayed.
NOTE: In installer setup mode only, each press of
the ▲key momentarily displays 01. Each
press of the ▼key momentarily displays
02. When the keys are released, these two-
digit codes are no longer displayed.
3. Press the ▲ key. Factory information is displayed. A
typical example is shown, but information displayed
varies by model. This information is for factory use
only.
4. Press the ▲ key again to display °C or °F.
System Cycles Per Hour
Steam, Gravity 1
Hydronic Heat, Condensing Gas
Furnacesa3
Gas or Oil Forced Air 6
Electric Heat 9
Special Applicationsb12
5. Press the ▼ key to change the °C or °F indication.
6. Press the ▲ key to display the heat cycle rate of 1,
3, 4, 5, 6, 9, or 12. If the desired cycle is displayed,
press the ▲ key to exit the installer setup mode. To
change the heat cycle rate, press the▼key to scroll
between 1, 3, 4, 5, 6, 9, and 12. Stop scrolling when
the desired rate is displayed. See Table 1 for the
cycle rate options and the corresponding system
equipment.
aHigh Efficiency Furnace.
bRefer to equipment manufacturer’s instructions.
NOTE: Steps 7 and 8 are available on select models.
7. Press the ▲ key to display cooling algorithm
configuration default.
M1468
4
M1468
5
M1469
0
M1468
6
M1468
7
M1468
8
M1468
9
M1841
9
8. Press the ▲ key to change cooling algorithm to C1
or C3.
C1 = Standard cooling algorithm.
C3 = Aggressive cooling algorithm (can cause
overshooting).
9. Press the ▲ key to save all changes, exit installer
setup mode and return to normal operation.
NOTE: After exiting installer setup mode, change the
setpoint to the desired room temperature.
CHECKOUT
Heating
1. Slide the SYSTEM switch to Heat and the FAN
switch to Auto.
2. Press and hold the ▲key to raise the temperature
setting several degrees above the room tempera-
ture. After approximately ten seconds, the heating
equipment should start. In conventional systems, the
system turns on the fan using a time delay relay or a
limit control. When using an electric heat thermostat,
the fan starts immediately.
3. Press the ▼ key to lower the temperature setting
below the room temperature. Heating equipment
should stop.
4, 5, 12

69-1493–1
7
T8400C ELECTRONIC THERMOSTAT
Cooling
CAUTION
Low Temperature Hazard.
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 equipment manufac-
turer instructions.
•For compressor protection, during power
interruption and on initial startup, the T8400C
Electronic Thermostat will go into a five minute
delay. During this delay, the cooling icon, a
snowflake , will flash.
1. Slide the SYSTEM switch to Cool and the FAN
switch to Auto.
2. Press the ▼ key to lower the temperature setting
several degrees below the room temperature. After
approximately five minutes, the cooling equipment
should start. The fan starts and stops with the
cooling equipment.
3. Press the ▲ key to raise the temperature setting
above the room temperature. Cooling system should
shut down.
NOTE: To bypass the five minute delay, see Optional
System Checkout section.
Fan
1. Slide the SYSTEM switch to Off and the FAN switch
to On. The fan should run continuously.
2. Slide the FAN switch to Auto. In heating, the fan is
controlled directly by the heating equipment and
may start a few minutes after the heating equipment
turns on (on most systems). When using an electric
heat thermostat, the fan starts and stops with the
heating equipment. In cooling, the fan starts and
stops with the cooling equipment.
Make certain all equipment responds properly to the
thermostat.

69-1493–1 8
T8400CELECTRONICTHERMOSTAT
69-1493–1 G.H. Rev. 2-02
Honeywell Limited-Honeywell Limitée
35 Dynamic Drive
Scarborough, Ontario
M1V 4Z9
Automation and Control Solutions
Honeywell
1985 Douglas Drive North
Golden Valley, MN 55422
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