T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS
11 68-0180-3
Fig. 19. T8400C power 0stealing internal schematic.
Fig. 20. T8401C hardwired internal schematic.
Energy Savings
You can save energy with the T8400C, T8401C and
T8424C,D Thermostats in the heating mode by lowering the
temperature setting 5°F (3°C) to 10°F (5°C) at night and
during the day. You can also save energy in the cooling mode
by raising the temperature settin g during the day before you
leave for work or school. Savings can be as high as 7% to
33% depending on your home, where you live, the number of
energy saving periods you choose and your energy savings
temperature settings. Refer to the maps in the Operation
section for typical energy savings.
Sequence of Operations
The Fan, Heat and Cool outputs are relay or mosfet
controlled. A loss of ac power or a change in the SYSTEM
switch setting can cause the outputs to turn off. The truth table
shows the sequence of operations for the FAN settings and
SYSTEM modes. See Table 3 Sequence of Operations.
L1
(HOT) L2
1
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
SYSTEM SWITCH
FAN SWITCH
AUTO
ON
OFF
HEAT
COOL
Y
W
G
R
FAN RELAY
COOL RELAY
HEAT RELAY
POWER
SUPPLY
LOGIC AND
CONTROL
THERMOSTAT
LOGIC
THERMISTOR
SENSOR
M10360
MOSFET
MOSFET
L1
(HOT)
L2
1
1POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.
SYSTEM SWITCH
FAN SWITCH
AUTO
ON
OFF
HEAT
COOL
C
Y
W
G
R
FAN RELAY
COOL RELAY
HEAT RELAY
POWER
SUPPLY
THERMOSTAT
LOGIC
THERMISTOR
SENSOR
RELAY
M10292