3. Press the s 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.
4. Press the s key again to display °C or °F.
5. Press the t key to change the °C or °F indication.
6. Press the s key to display the heat cycle rate of 1, 3,
4, 5, 6, 9, or 12. If the desired cycle is displayed,
press the s key to exit the installer setup mode. To
change the heat cycle rate, press the t key to scroll
between 1, 3, 4, 5, 6, or 9. Stop scrolling when the
desired rate is displayed. See Table 1 for the cycle
rate options and the corresponding system equip-
Table 1. Heating Cycle Rates.
Steam, radiant floor heat, gravity
Hydronic heat, condensing gas
Gas or oil forced air
High efficiency furnace.
Refer to equipment manufacturer's instructions.
NOTE: Steps 7 and 8 are available on select models.
7. Press the s key to display cooling algorithm config-
8. Press the s key again to change cooling algorithm
to C1 or C3.
C1 = Standard cooling algorithm.
C3 = Aggressive cooling algorithm (can cause
9. Press the s key again. Current configuration (CC) is
displayed. A typical example is shown, but CC varies
by model. (This information is for factory use only.)
Cycles Per Hour
4, 5, 12
T8400C AND T8401C ELECTRONIC THERMOSTATS
10. Press the s key to save all changes, exit installer
setup mode and return to normal operation.
NOTE: After exiting installer setup mode, change the
setpoint to the desired room temperature.
1. Slide the SYSTEM switch to Heat and the FAN
switch to Auto, if available.
2. Press and hold the s 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
3. Press the t key to lower the temperature setting
below the room temperature. Heating equipment
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
1. Slide the SYSTEM switch to Cool and the FAN
switch to Auto.
2. Press the t 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-
3. Press the s key to raise the temperature setting
above the room temperature. Cooling system
should shut down.
NOTE: To bypass the 5 minute delay, see the Optional
System Checkout section.
1. Slide the SYSTEM switch to Off and the FAN
switch to On. The fan should run continuously.
2. Slide the FAN switch to Auto. 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 equipment. In cooling, the fan starts and
stops with the cooling equipment.
Make certain all equipment responds properly to the