Quick answer
A heat pump fan that is not spinning is normal during a defrost cycle, which lasts 5 to 15 minutes, and on inverter units once the house is at temperature. It is a fault if the compressor runs and the fan stays still longer than 15 minutes. Likely causes are ice jamming the blades, a failed capacitor or motor, or the fan-driver board. Switch to emergency heat and call.
If your heat pump fan is not spinning, listen before you worry. A silent outdoor unit with a still fan may simply have nothing to do. The combination that matters is a compressor you can hear humming or droning while the fan blade above it sits still. That is either a defrost cycle, which ends by itself, or a fault that will shut the unit down on a pressure trip.
When a stopped outdoor fan is normal
- Defrost: the board stops the fan on purpose so the coil warms quickly and sheds its frost. You will hear a whoosh as the valve shifts and see steam, and the fan restarts when the cycle ends.
- Demand satisfied on an inverter unit: variable-speed systems slow the fan to a crawl, or stop it, when the house is at setpoint.
- Start-up delay: after a power interruption or a thermostat change, the outdoor unit waits several minutes before starting.
- Hybrid lockout: on a heat pump paired with a gas furnace, the thermostat hands heating to the furnace below a set outdoor temperature and the outdoor unit sits idle.
Faults that stop the fan while the compressor runs
Four parts account for most stuck fans, and each fails in a recognisable way:
- Ice jamming the blades: freezing rain, a drift on top of the unit or a failed defrost builds ice into the fan opening. The motor hums against it and overheats. How to defrost a frozen heat pump covers the safe way to clear it.
- Run capacitor: on single-stage units the fan motor needs a capacitor to start. When it weakens, the motor hums, the blade twitches or turns slowly, and the top of the unit gets hot.
- Fan motor: bearings seize after years of weather, or a winding burns open. A blade that is stiff to turn with the power off, or wobbles on its shaft, points to the motor.
- Inverter fan-driver board: variable-speed units use a DC fan motor driven by electronics on the outdoor board, with no capacitor at all. Either the motor or the driver circuit fails, and the unit usually shows an error code on the indoor display.
What happens when the compressor runs without the fan
The coil needs moving air to exchange heat. In cooling mode, without the fan, refrigerant pressure climbs quickly until the high-pressure switch shuts the compressor off. In heating mode the opposite happens: the coil cannot pick up heat, pressure on the suction side falls, the coil ices solid and the low-pressure safety trips.
The unit then rests, restarts and trips again. Each round is hard on the compressor, the most expensive part in the cabinet. The decision rule: compressor running and fan still for more than 15 minutes, which is longer than any defrost, means switch the thermostat to Emergency Heat, or Off if you have no backup, and call. When to use emergency heat explains what that setting does.
Check this yourself first
- Thermostat: confirm it is calling for heat or cooling and that the setpoint is past room temperature.
- Sound: stand beside the unit. Silence means no call or no power. A steady hum with a still blade is the fault described on this page.
- Time: note the clock. If the fan restarts on its own after a steamy pause, that was defrost.
- Look, do not reach: check through the top grille for ice, a branch or a toy stopping the blade. Switch off the outdoor disconnect before removing anything, because the fan starts without warning.
- Breaker: if nothing runs at all, reset the breaker once. A unit with no fan and no compressor is a power or control problem; see why a heat pump will not turn on.
Skip the old trick of pushing the blade with a stick to get it going. It proves the capacitor is weak, but it puts your hand beside a live fan and tells you nothing a meter would not.
What a heat pump fan repair costs
- Diagnostic visit: $90–$150, taken off the repair bill if you proceed.
- Capacitor replacement: $150–$350, the least expensive outcome.
- Outdoor fan motor: $300–$700 depending on the motor type.
- Outdoor control board on an inverter unit: boards are typically $400–$800, confirmed in a written quote once the model is known.
A fan fault caught on day one is a capacitor or a motor. Left to trip for a week, it can take the compressor with it. ZK Mechanical carries out heat pump repair across Burlington, Oakville, Hamilton and Mississauga with no overtime, weekend or holiday surcharge; reach the emergency line at (647) 801-1252 or request a visit.