69-1494–1
4
T8400B,C; T8401C ELECTRONIC THERMOSTATS
Fig. 7. T8400C/T8401C heat-cool wiring
diagram in single transformer system
with gas heat/electric cooling.
Fig. 9. Mounting thermostat to wallplate.
T8400C shown here.
OPERATION
Setting FAN and SYSTEM Switches
Fan and system settings are controlled manually by
using the switches located at the bottom of the thermo-
stat case. See Fig. 10.
NOTE: Switch availability is model dependent.
Fig. 8. T8400C/T8401C heat-cool wiring
diagram in oil heating/electric cooling system.
Oil primary has its own transformer.
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.
M11025B
FAN
SYSTEM
Auto On
Cool Off Heat
DASHED LINES INDICATE TABS
ON BACK OF THERMOSTAT
FAN
SYSTEM
Auto
Cool Off Heat
ENGAGE TABS AT TOP
OF THERMOSTAT WITH
SLOTS ON WALLPLATE.
A
B
PRESS LOWER EDGE OF
CASE TO LATCH.
Set
Room
Set
Room
FAN
SYSTEM
Auto On
Cool Off Heat
INCREASE
SETTING
DECREASE
SETTING
SYSTEM SWITCH
FAN SWITCH
TEMPERATURE DISPLAY
M11020A
Set
Room
Fig. 10. T8400C Digital Display and Switches.
FAN Switch (Not Available on all Models)
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 (on most
systems). When using an electric heat thermostat,
the fan starts and stops with the heating equip-
ment.
On: The fan runs continuously. Use for improved air
circulation and air quality.
Slide the switch in the bottom left corner of the thermo-
stat to select the desired fan setting.
L1
(HOT)
L2
1
2
1
2
W
Y
G
R
C
COOLING
CONTACTOR
FAN
RELAY
HEATING
PRIMARY
CONTROL
24V
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
IN T8401C INSTALLATIONS ONLY, CONNECT C TERMINAL.
M10977
T8400C, T8401C
L1
(HOT)
L1
(HOT)
L2
L2
1
1
2
1
W
Y
G
R
C
2
COOLING
CONTACTOR
FAN
RELAY
OIL PRIMARY
CONTROL
T
T
24V
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
IN T8401C INSTALLATIONS ONLY, CONNECT C TERMINAL.
M10978
T8400C, T8401C
