Why Is My Heat Pump’s Outdoor Fan Not Spinning?

Quick answer: In winter, a heat pump’s outdoor fan that stops for a few minutes while the unit whooshes or steams is usually just a normal defrost cycle. If the fan stays still while the unit hums, or nothing runs at all, the usual culprit is a failed capacitor, fan motor, contactor or control board, and that needs a technician.

Is it normal for a heat pump fan to stop in winter?

Often, yes, if it’s cold and damp outside. A heat pump in heating mode grows frost on its outdoor coil, so every so often it runs a defrost cycle: it briefly switches to cooling to warm the coil, and it holds the outdoor fan off so the coil heats faster. InterNACHI, the home inspectors’ association, puts a typical defrost cycle at about 30 seconds to a few minutes.

You may hear a whoosh as the reversing valve (the part that swaps the unit between heating and cooling) shifts, and steam often rolls off the unit. Then the fan restarts and heating resumes. In Austin this happens on raw mornings in the 30s, not only in a hard freeze. The water that runs off is normal too, as explained in why water drips from a heat pump in winter.

Why is the outdoor unit humming but the fan won’t spin?

A humming unit with a still fan usually has a failed part, most often the capacitor, fan motor, contactor or control board. If the fan stays still well past a normal defrost, switch the thermostat to Emergency Heat, or off, and call for service. Without its fan, the outdoor coil can’t trade heat with the air. Pressures run out of range, and the compressor (the pump that moves refrigerant) overheats and trips its safeties. Each trip wears on it. Here’s what each suspect does:

• A weak or failed capacitor. This small part stores the jolt the fan motor needs to start, and Texas heat wears capacitors out.
• A worn fan motor. Bearings dry out and windings overheat. A motor that starts, runs a bit and quits is a classic sign.
• A stuck or burned contactor. This switch sends power to the outdoor unit.
• A faulty control or defrost board. This circuit board decides when the fan runs.
• Something in the way. A stick, a vine or ice packed around the blade can stop it cold.

What if the heat pump won’t turn on at all?

Usually it’s power or settings, so check those first. Make sure the thermostat is set to heat or cool and has fresh batteries if it uses them. Then check the breaker for the outdoor unit.

If the breaker has tripped, you can reset it once, but if it trips again, leave it off and call. If the power just came back after an outage, see how to restart your AC after a power outage. Beyond that, it’s electrical work: Gold Eagle’s technicians repair heat pumps around Austin.

Can you push-start a heat pump fan with a stick?

No. It’s a popular internet trick for starting a fan with a bad capacitor, and a bad idea. Capacitors hold a charge, the blade can take off without warning, and running a motor on a failing capacitor cooks the motor.

Here’s what you can safely do: look from outside the unit, and with the power off at the disconnect (the shutoff box on the wall by the unit), clear leaves and debris from around it. Keep the area open.

Is a heat pump fan that won’t spin an emergency in winter?

Usually not. It’s rarely dangerous, but the house will run on backup heat until the repair. With the outdoor unit down, most heat pump systems switch to the electric heat strips, if yours has them: backup heaters in the indoor unit that keep you warm but use far more electricity than the heat pump. Aux heat vs. emergency heat explains which setting to use until the repair.

What should you do next?

• Watch the unit for a few minutes: steam followed by a restart means it was defrost.
• Switch the thermostat to Emergency Heat, or off, if the fan stays still while the unit hums.
• Check the thermostat setting and the outdoor breaker if nothing runs at all.
• Schedule a Gold Eagle repair and run on backup heat until the technician arrives.

Related guides: Aux Heat vs. Emergency Heat: What Your Heat Pump Thermostat Is Telling You and Why Is Water Dripping From Your Heat Pump in Winter?

About Gold Eagle Services: This guide comes from the team at Gold Eagle Services, a family-run Austin HVAC, indoor air quality and mold remediation company founded in 2017. We’re licensed (TACLA119235 and RCO1783), insured and bonded, and we serve homes across the greater Austin area.

Need help with this in your home? Learn about our heat pump repair and installation, or call 512-489-4653 to schedule a visit.

Related Gold Eagle service: AC repair in Austin