69-1493–1
4
T8400C ELECTRONIC THERMOSTAT
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
2
4
R
B
O
M12562
L1
(HOT)
L2
FAN
RELAY
HEAT
RELAY
L1
(HOT)
L2
COMPRESSOR
CONTACTOR
HEATING
TRANSFORMER
COOLING
TRANSFORMER
HEAT
DAMPER
COOL
DAMPER
1
POWER 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.
L1
(HOT)
L2
1
COOL
CHANGEOVER
FAN
RELAY
COOL
RELAY
HEAT
RELAY
24V
M13277A
HEAT
CHANGEOVER
TRANSFORMER
1
POWER 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 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