Honeywell TRADELINE T8400C User manual

® U.S. Registered Trademark
Copyright © 2004 Honeywell International Inc. • • All Rights Reserved
INSTALLATION INSTRUCTIONS
69-1740
T8400C, T8401C
Electronic Thermostats
The T8400C and T8401C Thermostats provide single-
stage, non-programmable temperature control for 24V
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/
cooling system controls. The T8401C requires a common
wire for operation. Batteries are not required because
setpoints are held permanently by non-volatile memory.
The T8400C and T8401C models include 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.
Contact your local waste management authority
for instructions regarding recycling and the
proper disposal 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 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
Electrical Shock or Equipment Damage
Hazard.
Can shock individuals or 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.
Mounting Wallplate to Wall
IMPORTANT
Level only for appearance. The thermostat func-
tions normally even when not level.
Mount the T8400C and T8401C 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 entrance hole
on the wallplate.
3. Fasten the wallplate to the wall using the anchors
and screws provided.
4. After wiring the wallplate, plug the hole to prevent
drafts from affecting the thermostat; see Wiring
section.

T8400C, T8401C ELECTRONIC THERMOSTATS
69-1740 2
Fig. 1. Typical location of thermostat.
Fig. 2. Mounting wallplate to wall.
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.
Wiring
IMPORTANT
Use an 18-gauge maximum wire to wire the
T8400C and T8401C Thermostats.
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
acceptable. See Fig. 5.
Refer to Fig. 6 through 10 for typical wiring hookups.
Fig. 3. Fan operation (fuel) switch.
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
M12580
FAN OPERATION (FUEL) SWITCH
F
E

T8400C, T8401C ELECTRONIC THERMOSTATS
3 69-1740
Fig. 4. Restrict wiring to shaded area
(T8400C shown).
Fig. 5. Wiring connections
(T8400C shown).
Fig. 6. Typical hookup of T8400C in heat-cool system
with single transformer.
Fig. 7. Typical hookup of T8400C in heat-cool system
with two transformers.
Fig. 8. Typical hookup of T8400C in single-stage heat
pump systems.
KEEP WIRING IN
SHADED AREA
MOUNTING
SCREW HOLE
MOUNTING
SCREW HOLE
WIRING ENTRANCE
HOLE
M16432
G
Rc
R
Y
W
B
O
TERMINAL
SCREW
M13274
G
Rc
R
Y
W
B
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
R
B
O
2
2
Y
G
Rc
W
24
R
B
O
FAN
RELAY
HEAT
RELAY
COMPRESSOR
CONTACTOR
HEATING
TRANSFORMER
COOLING
TRANSFORMER
HEAT
DAMPER
COOL
DAMPER
3
3
L1
(HOT)
L2
1
L1
(HOT)
L2
1
M12562A
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
4
L1
(HOT)
L2
1
COOL
CHANGEOVER
FAN
RELAY
COMPRESSOR
24V
M20880
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.
FIELD INSTALLED JUMPER.
2
3
4
4
2
2
Y
G
Rc
W
R
B
O
3

T8400C, T8401C ELECTRONIC THERMOSTATS
69-1740 4
Fig. 9. Typical hookup of T8401C in heat-cool system.
Fig. 10. Typical hookup of T8401C in single-stage
heat pump system.
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. 11.
Fig. 11. Mounting thermostat wallplate.
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. 12.
FAN Switch
Fan switch settings are:
On: The fan runs continuously. Use for improved air
circulation and air quality.
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 (on most systems).
When using an electric heat thermostat, the fan
starts and stops with the heating equipment.
Slide the FAN switch in the bottom left corner of the
thermostat to select the desired fan setting.
L1
(HOT)
L2
1
FAN
RELAY
COOL
RELAY
HEAT
RELAY
24V
M20881
TRANSFORMER
1POWER SUPPLY. PROVIDE DISCONNECT MEANS
AND OVERLOAD PROTECTION AS REQUIRED.
Y
G
C
W
R
B
O
L1
(HOT)
L2
1
COOL
CHANGEOVER
FAN
RELAY
COMPRESSOR
24V
M20882
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.
FIELD INSTALLED JUMPER.
2
3
2
2
Y
G
C
W
R
B
O
3
M14677A
SYSTEM
Cool Off Heat
Auto On
FAN
DASHED LINES INDICATE TABS
ON BACK OF THERMOSTAT
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

T8400C, T8401C ELECTRONIC THERMOSTATS
5 69-1740
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.
Fig. 12. Digital display and system
switches (FAN and SYSTEM).
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. 12.
2. To display the temperature setpoint 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, the
heat cycle rate and the C3/C1 temperature
control, tap the ▲ key until exiting the installer
setup.
To set the °F/°C indication, the heat cycle rate and the
C3/C1 temperature control:
1. If the temperature is displayed in °F, set the tem-
perature setpoint to 52°F. If the room temperature
is displayed in °C, set the temperature setpoint to
11°C.
OPTIONAL SYSTEM CHECKOUT
When in steps 2 and 3 only, 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 dis-
played.
SYSTEM
Cool Off Heat
Auto On
FAN
M14678A
INCREASE SETTING
DECREASE SETTING
FAN SWITCH
Set Room
Set Room
INDICATOR
ROOM TEMPERATURE
SETPOINT TEMPERATURE
M14679
M14680
M14681
M14682
M14683
M14684
M14685
M14686

T8400C, T8401C ELECTRONIC THERMOSTATS
69-1740 6
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 dis-
played varies by model. This information is for fac-
tory use only.
4. Press the ▲ key again to display °C or °F.
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. To change the heat cycle rate,
press the ▼key to scroll between 1, 3, 4, 5, 6, 9, or
12. Stop scrolling when the desired rate is dis-
played. See Table 1 for the cycle rate options and
the corresponding system equipment.
7. Press the ▲key to display heating/cooling temper-
ature control default..
8. Press the ▼ key again to change heating/cooling
temperature control to C1 or C3.
C1 = Standard heating/cooling temperature
control.
C3 = Aggressive heating/cooling temperature
control (can cause room temperature to
overshoot the setpoint).
9. Press the ▲key again. Factory information (varies
by model) is shown.
Table 1. Heating Cycle Rates.
aHigh efficiency furnace.
bRefer to equipment manufacturer’s instructions.
10. Press the ▲key to save all changes, exit installer
setup mode and return to normal operation.
NOTE: After exiting installer setup mode, slide the
System switch to the desired position and
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 through the use of a
time delay relay or through 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.
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 manufacturer’s
recommendations.
• For compressor protection, during power
interruption and on initial startup, the T8400C
and T8401C Thermostats go into a five-minute
delay. During this delay, the cooling icon (a
snowflake ❄) flashes.
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 cool-
ing equipment.
M14687
M14688
M14689
M14690
M18419A
M18420
System Cycles Per Hour
Steam, gravity 1
Hydronic heat, condensing gas
furnacea
3
Gas or oil forced air 6
Electric heat 9
Special applicationsb4, 5, 12

T8400C, T8401C ELECTRONIC THERMOSTATS
7 69-1740
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 the
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 equip-
ment 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.
Be sure all equipment responds correctly to the
thermostat.

69-1740 J.S. 6-04 www.honeywell.com/yourhome
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