12
Thermidistat Control Troubleshooting
SYMPTOM
WHAT TO CHECK
No Display
Open Thermidistat Control. Check for 24vac between R and C at screw terminals on mount-
ing base. Reassemble, making sure pins on board engage sockets in mounting base. If
display does not appear, replace Thermidistat Control.
“--- ---” in place of room temperature
Thermidistat Control cannot properly read room temperature. Replace Thermidistat Control.
“E3” or “--- ---” in place of outdoor
temperature
Thermidistat Control cannot properly read outdoor temperature. Check outdoor sensor and
its wiring.
“E4” or “E5”
Internal failure. Replace Thermidistat Control.
“E6”
System is stuck in defrost. Check wiring and heat pump defrost control board.
“Clean Filter” icon displayed
Filter timer has expired. Clean or replace filter and then press VACATION and HOLD/END
buttons together to reset.
Cooling or heating will not come on
See Installer Setup to force heating or cooling. Check for 24vac at equipment terminals. If
not present, check wiring.
Humidify or dehumidify will not come on
See Installer Setup to force HUM or DEHUM. Check for 24vac at equipment terminals. If not
present, check wiring.
TST
AT
