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T8535L MICROELECTRONIC COMMUNICATING NONPROGRAMMABLE THERMOSTAT
TROUBLESHOOTING GUIDE
Symptom
Display does not
Thermostat is not powered. Check for 24 Vac between C and R terminals; if missing 24 Vac:
turn on.
Thermostat microprocessor
is locked up.
Temperature
Room temperature display
display is incorrect.
has been reconfigured.
Thermostat is configured for
°F or °C display.
Bad thermostat location.
The upper or lower
Temperature
temperature limits were
settings will not
reached.
change. (Example:
Cannot set the
The setpoint temperature
heating higher or
range stops were
the cooling lower.)
configured.
Heating does not
No power to the thermostat. Check for 24 Vac between C and R terminals; if missing 24 Vac:
turn on.
Heating does not
Thermostat minimum off
turn on.
time is activated.
System selection is not set
to Heat.
Cooling does not
No power to the thermostat. Check for 24 Vac between C and R terminals; if missing 24 Vac:
turn on.
Thermostat minimum off
time is activated.
System selection is not set
to Cool.
Home and Building Control
Honeywell Inc.
Honeywell Plaza
P.O. Box 524
Minneapolis, MN 55408-0524
69-1307—1
69-1307—1 G.H. Rev. 8-99
Possible Cause
Home and Building Control
Honeywell Limited-Honeywell Limitée
155 Gordon Baker Road
North York, Ontario
M2H 3N7
— Check if the circuit breaker is tripped; if so, reset the circuit
breaker.
— Check if the system fuse is blown; if so, replace the fuse.
— Check if the power switch on the HVAC equipment is in the Off
position; if so, set to the On position.
— Check wiring between the thermostat and HVAC equipment;
replace any broken wires and tighten any loose connections.
— If 24 Vac is present, proceed with troubleshooting.
Remove the thermostat from the wallplate for two minutes. After
two minutes, replace the thermostat on the wallplate.
Enter Installer Setup mode number 37 and reconfigure the display.
Enter Installer Setup mode number 14 and reconfigure the display.
Relocate the thermostat.
Check the temperature setpoints:
• Heating limits are 40°F to 90°F (4.5°C to 32°C).
• Cooling limits are 45°F to 99°F (7°C to 37°C).
Check Installer Setup mode numbers 34 and 35 and reconfigure
the setpoint stops.
— Check if the circuit breaker is tripped; if so, reset the circuit
breaker.
— Check if the system fuse is blown; if so, replace the fuse.
— Check if the system switch at the equipment is in the Off
position; if so, 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.
— Check connection to D terminal.
Wait up to five minutes for the system to respond.
Set system selection to Heat.
— Check if the circuit breaker is tripped; if so, reset the circuit
breaker.
— Check if the system fuse is blown; if so, replace the fuse.
— Check if the system switch at the equipment is in the Off
position; if so, 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.
— Check connection to D terminal.
• Wait up to five minutes for the system to respond.
• Enter Installer Setup mode number 33. Reconfigure minimum
off time (if required).
Set system selection to Cool.
Printed in U.S.A. on recycled
paper containing at least 10%
8
post-consumer paper fibers.
Action
www.honeywell.com/yourhome
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