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69-0917—2
7
T8112C,D ELECTRONIC PROGRAMMABLE THERMOSTATS
TROUBLESHOOTING GUIDE
NOTICE
This equipment is a Class B digital apparatus, which complies with Canadian Radio Interference Regulations, CRC
c.1374.
If… Then…
Display will not come on. • Set the system switch to OFF. Remove batteries. Insert batteries
backward for at least five seconds to reset thermostat. Correctly replace
batteries. Display should come on.
• Make sure batteries are fresh and installed correctly.
• Gently clean battery contacts using a soft pencil eraser. Do not use
anything abrasive on the clips.
Temperature display will not go lower
than 45° F (7° C) or higher than 88° F
(31° C) during programming.
• The temperature setting limit is reached. The setting range is 45° F to
88° F (7° C to 31°C).
Temperature change occurs at the
wrong times.
• Check the program times for the period in question. Be sure that AM and
PM indications are correct. Make sure the current day and time are
correct. Reprogram if necessary.
Heating will not come on. • Check that switch on thermostat is set to HEAT. Allow a minimum of five
minutes for time guard protection to expire.
• Check the system fuse or circuit breaker and replace or reset if
necessary.
• Check for correct wiring and good connections.
• Disconnect and jumper wires R and W. If heat does not come on, check
out the heating system.
• If display is blank or says “bAt Lo,” install fresh batteries.
Cooling will not come on. • Check that switch on thermostat is set to COOL. Allow a minimum of five
minutes for time guard protection to expire.
• Check the system fuse or circuit breaker and replace or reset if
necessary.
• Check for correct wiring and good connections.
• Disconnect and jumper wires R and Y. If cooling does not come on,
check out the cooling system.
• If display is blank or says “bAt Lo,” install fresh batteries.
• The thermostat has a built-in time delay on cooling. Allow at least five
minutes after changing the setting before the air conditioner starts.
• Make sure outdoor disconnect is engaged (on).
• If temperature setting is lower than current temperature, and SYSTEM
ON indicator is lit, move system switch from COOL to OFF for ten
minutes. After ten minutes, return switch to COOL position. If air
conditioner comes on, compressor could have reached its high limit
temperature protection and shut down.
• If 2- or 4-wire installation, verify that R-Rc jumper is installed
Too warm or too cool. • Press Run Program key to check the current temperature setting.
• If desired, change the temperature setting. See the Owner’s Manual.
SYSTEM ON indicator is lit, but no heat
is coming from the registers.
• Allow time for the furnace to heat up and the fan to come on before
checking for heat at the register. (Check to make sure the Cycle Rate in
the Installation section is correct.)
Thermostat current temperature setting
does not match the display temperature
to within ± 1°.
• Check that the wiring hole in the wall behind the wallplate has been
plugged with insulation to prevent drafts that might adversely affect
thermostat operation.
• Be aware that it is normal for the current setting and display temperature
to differ on occasion.
• During recovery from setback or setup, setting and display temperatures
can differ for up to 30 minutes after recovery period.
bAtLo remains on display after batteries
are installed.
Remove batteries. Wait one hour. Install fresh Alkaline batteries.