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Symptom
Heating will not
No power to the thermostat.
come on.
Thermostat minimum off time
is activated.
System selection is not set to
Heat.
Cooling will not
No power to the thermostat.
come on.
Thermostat minimum off time
is activated.
System selection is not set to
Cool.
Fan operation set for 00
System on indicator
(conventional heat) when it
(flame=heat,
should be set for 01 (electric
snowflake=cool) is
heat).
displayed, but no
warm or cool air is
Conventional heating
coming from the
equipment turns on the fan
registers.
when the furnace has
warmed up to a setpoint.
Heating equipment is not
operating.
System on indicator
Option not activated.
is not displayed,
but heating or
cooling system is
operating
Outdoor
Option not activated.
temperature
a
not displayed
Outdoor sensor is connected
Outdoor
incorrectly.
temperature
a
display is incorrect
Wrong sensor.
a
Available on select models.
Troubleshooting Guide (Continued).
Possible Cause
T8501D DELUXE ZONE THERMOSTAT
• Check that C terminal is connected to the system transformer.
• Check for 24 Vac between C and R and between R and W
terminals.
— If missing 24 Vac:
— check if the circuit breaker is tripped—reset the
circuit breaker.
— check if the system fuse is blown—replace the fuse.
— check if the system switch at the equipment is in the
Off position—set to On position.
— check wiring between thermostat and HVAC
equipment—replace any broken wires and tighten
any loose connections.
— If 24 Vac is present, proceed with troubleshooting.
Wait up to five minutes for the system to respond.
Set system selection to Heat.
• Check that C terminal is connected to the system transformer.
• Check for 24 Vac between C and R and between R and Y
terminals.
— If missing 24 Vac:
— check if the circuit breaker is tripped—reset the
circuit breaker.
— check if the system fuse is blown—replace the fuse.
— check if the system switch at the equipment is in the
Off position—set to the On position.
— check wiring between thermostat and HVAC
equipment—replace any broken wires and tighten
any loose connections.
— If 24 Vac is present, proceed with troubleshooting.
• Wait up to five minutes for the system to respond.
• Enter Installer Setup number 33. Reconfigure minimum off
time (if required).
Set system selection to Cool.
Enter Installer Setup number 02 and reconfigure the fan
operation.
Wait a minute after seeing the On indicator and then check the
registers.
Verify operation of heating equipment in self-test.
Enter Installer Setup number 36 and reconfigure to 00.
Enter Installer Setup number 24 and set to 01. Thermostat must
have OT terminals and a C7089B1000 installed.
Refer to C7089B1000 installation instructions and check wiring
between the thermostat and sensor.
Replace sensor with C7089B1000 sensor.
9
Action
69-1049—1
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