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Condenser Fan Not Spinning: Capacitor, Motor or Control?

By HVAC Cheat Sheet Team · Updated · 2 min read

With no condenser airflow, head pressure and compressor temperature climb within minutes. If you find the compressor running with the fan stopped, shut it down while you diagnose.

First, rule out "normal"

  • Heat pump defrost: the outdoor fan stops on purpose during defrost. Check the defrost board or wait a few minutes.
  • Variable-speed and communicating systems may stage the fan down or stop it at low ambient or low load. Check the unit's status codes.
  • Low-ambient fan cycling controls on some systems turn the fan off on purpose to hold head pressure.

1. Fan capacitor

On a PSC fan motor, a weak or open run capacitor is the most common failure. On a dual capacitor, test the FAN to C side against its microfarad rating. A blade that starts when you give it a push (careful, and only with an insulated tool) is classic weak-capacitor behavior. See how to test a run capacitor, or use the capacitor check calculator for an under-load test.

2. Seized or dragging bearings

With power off and locked out, spin the blade by hand. It should spin freely and coast. Stiff, gritty or wobbling rotation means worn bearings. Replace the motor; oiling dry bearings rarely lasts.

3. Motor overheated or winding failure

A motor that's hot to the touch with an open internal thermal protector will read open until it cools. Once it's cool, check windings for continuity and to ground. An open or grounded winding means the motor needs replacing.

4. Power and controls

  • Contactor: on most residential condensers the fan and compressor run through the same contactor. Check for voltage on the load side, and look for one burned-open pole.
  • Wiring: look for a broken or burned wire at the contactor, capacitor or motor. Rodents and vibration take their toll.
  • Defrost board or fan relay (heat pumps): a failed outdoor fan relay leaves the fan off even outside defrost.
  • ECM fan motors: check line voltage and the control signal to the motor module, per the manufacturer's procedure.

When replacing the motor

Match horsepower, RPM, rotation direction, voltage, frame and the required capacitor. Set the blade at the same height in the shroud as the original. A blade set too high or too low cuts airflow and raises head pressure.

FAQ

Can I run the AC with the condenser fan not working?

No. Without condenser airflow, head pressure and compressor temperature rise quickly, tripping the compressor overload and stressing the compressor.

Why does the fan start when I push it?

The motor has power but not enough starting torque, almost always a weak fan capacitor. Bearings that drag can do the same thing, so check both.

Does the outdoor fan stop during heat pump defrost?

Yes. In defrost the system runs in cooling mode and the outdoor fan is turned off so the coil heats up and melts the frost.

Sources

Tools for this job

µF

Capacitor Check Calculator

Measured amps and volts to microfarads, with a pass/fail against the rated value.

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