Possible Cause: Fan is not being called.
Corrective Action: Verify controller or thermostat is calling for fan operation.
Possible Cause: Electrical power issue.
Corrective Action: Verify power to the unit and to the fan contactor matches nameplate. For three phased units, verify unit is not single-phasing.
Possible Cause: Control circuit is open.
Corrective Action: Verify 24VAC to fan contactor holding coil. Trace out 24VAC power and determine where signal is lost if contactor does not pull in. Replace any defective components.
Possible Cause: Bad start capacitor.
Corrective Action: Verify capacity operation. Replace any defective components.
Possible Cause: Fan locked out on alarm.
Corrective Action: For controllers: clear alarm and reset system enable to AUTO. For thermostat/control by others, alarm may require unit power to be cycled.
Possible Cause: No control signal to VFD/ECM.
Corrective Action: Verify 0-10 VDC signal from controller to VFD or ECM.
Possible Cause: Motor has shorted or grounded.
Corrective Action: Ohm out fan motor. Replace fan motor if defective.