T8400C1099, T8401C1031 ELECTRONIC THERMOSTATS
NOTE: In installer setup mode only, each press of the
Table 1. Heating Cycle Rates.
System Cycles Per Hour
key momentarily displays 01. Each press of
the ▼key momentarily displays 02. When the
keys are released, these two-digit codes are no
Hydronic heat, condensing gas
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.
Gas or oil forced air
4, 5, 12
High efficiency furnace.
Refer to equipment manufacturer’s instructions.
Press the ▼ key again to display °C or °F.
0. 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
Press the ▼key to change the °C or °F indication.
Press the ▼ key to display the heat cycle rate of 1,
, 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
2. Stop scrolling when the desired rate is dis-
Slide the SYSTEM switch to Heat and the FAN
switch to Auto.
played. See Table 1 for the cycle rate options and
the corresponding system equipment.
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
Press the ▼ key to display heating/cooling temper-
ature control default..
Press the ▼key to lower the temperature setting
below the room temperature. Heating equipment
Press the ▼key again to change heating/cooling
temperature control to C1 or C3.
C1 = Standard heating/cooling temperature
C3 = Aggressive heating/cooling temperature
control (can cause room temperature to
overshoot the setpoint).
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
Press the ▼ key again. Factory information (varies
by model) is shown.
For compressor protection, during power
interruption and on initial startup, the T8400
and T8401 Thermostats go into a five-minute
delay. During this delay, the cooling icon (a
snowflake ▼) flashes.
Slide the SYSTEM switch to Cool and the FAN
switch to Auto.
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-