Setting Fan And System Switches; Operation; Mounting Thermostat To Wallplate; T8400C Digital Display And Switches - Honeywell T8400B Installation Instructions Manual

T8400B,C; T8401C ELECTRONIC THERMOSTATS
T8400C, T8401C
W
Y
G
R
C
2
1
L1
(HOT)
24V
L2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
1
OVERLOAD PROTECTION AS REQUIRED.
2 IN T8401C INSTALLATIONS ONLY, CONNECT C TERMINAL.
Fig. 7. T8400C/T8401C heat-cool wiring
diagram in single transformer system
with gas heat/electric cooling.
T8400C, T8401C
W
Y
G
R
C
2
L1
(HOT)
1
L1
L2
(HOT)
24V
L2
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
1
OVERLOAD PROTECTION AS REQUIRED.
2
IN T8401C INSTALLATIONS ONLY, CONNECT C TERMINAL.
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.
69-1494–1
COOLING
CONTACTOR
FAN
HEATING
RELAY
PRIMARY
CONTROL
COOLING
CONTACTOR
FAN
RELAY
1
T T
OIL PRIMARY
CONTROL
DASHED LINES INDICATE TABS
ON BACK OF THERMOSTAT
Set
Room
FAN
Auto On
A
ENGAGE TABS AT TOP
OF THERMOSTAT WITH
SLOTS ON WALLPLATE.
M10977
M11025B
Fig. 9. Mounting thermostat to wallplate.

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.
M10978
Set
FAN
Auto On
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.
4
SYSTEM
Cool Off Heat
B
PRESS LOWER EDGE OF
CASE TO LATCH.
T8400C shown here.
TEMPERATURE DISPLAY
Room
SYSTEM
Cool Off Heat
FAN SWITCH
SYSTEM SWITCH
Set Room
FAN SYSTEM
Cool Off Heat
Auto
INCREASE
SETTING
DECREASE
SETTING
M11020A