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“Why is my AC fan not spinning?”

This query is one of the most frequently asked questions we hear in the HVAC world. Perhaps you noticed that you were no longer getting cool air through your vents and went outside for a quick inspection of the AC unit. No matter what led you to discover that your AC fan is no longer spinning, it’s important to understand that this kind of behavior is not normal for an air conditioning unit. The fan in an air conditioning unit plays a vital role of blowing air across the cooling media—whether that’s refrigerant-filled condenser coils (in a standard refrigerated AC unit) or water-soaked pads (in an evaporative AC system). If the fan is not spinning, then a crucial function of your unit isn’t working. You won’t be able to restore cool airflow in your home until you can get that fan spinning again.

Diagnosing the “AC Fan Not Spinning” Problem

There are two basic variations on the “AC fan not spinning” problem.

AC Fan The first variation is when your AC unit seems to be running, but the fan still isn’t spinning. In this scenario, you will be able to hear the compressor working—usually with a buzzing or humming sound—but won’t be getting any cold airflow in your home. In most cases, this scenario indicates that your AC unit has a bad fan motor or a broken start capacitor. The fan motor, of course, is responsible for keeping the fan spinning. The capacitor is a battery-like component that creates a jolt of electricity to start the motor. Just as it takes more gasoline to start a car than to keep it idling, it also takes more energy to start a fan motor in an AC motor than it does to keep it running. If the capacitor can’t deliver that energy, then the fan motor cannot start or run. As such, either of these issues can be the culprit behind an AC fan that isn’t spinning.

The good news is that it’s pretty easy to figure out which component is bad. Find a thin, long wooden stick and insert it through the grate at the top of your AC unit. Gently give one of the blades of the fan a push. If the fan starts spinning and keeps spinning, then the problem is likely the start capacitor and not the motor. By giving the blades that nudge, you essentially have recreated the jolt of electricity that the capacitor needs to send to get the fan/fan motor going. If the fan blade doesn’t start spinning, or only spins as far as you push it, then the fan motor is probably the culprit. (Caution: do not try to use your fingers for this test process, or any kind of conductive metal; either can be dangerous.)

In either case, you will need to call your HVAC technician to replace the capacitor or the fan motor in your unit. In the meantime, go to your thermostat and turn off the air conditioning. You don’t want your unit’s compressor running for a long time without the fan, as it risks overheating the compressor and damaging it. Replacing a compressor is much more expensive than replacing a capacitor or fan motor.

Dust Mites in your HVAC Ducts

The second variation of the “AC fan not spinning” problem is when your AC unit seems to have no power at all. When you turn on your air conditioning, your unit will stay completely dormant: no spinning fan, no compressor buzz. Most customers assume this version of the issue is more serious because surely an AC unit with one functional piece (the compressor) is better than a unit with seemingly no functional components. However, in the vast majority of cases, an AC unit that has no power isn’t actually damaged at all; it’s just not receiving any power, period. In all likelihood, the circuit that powers your outdoor unit tripped. Switch off your AC at the thermostat and then go to your circuit breaker box to reset the breaker. When you turn on the AC again, you should hear the compressor and the fan start

If this process doesn’t solve the problem, or if your breaker quickly trips once more, call an HVAC technician. The problem could be a damaged compressor connector on your unit, or it could be a wiring or installation issue. An HVAC expert should be able to recommend the ideal next steps.

Don’t Forget Your Annual Air Conditioning Inspection

As you troubleshoot your “AC fan not spinning” issue, remember that you can avoid many common air conditioning problems by having your unit serviced at least once per year. The last thing you want is to contend with a broken unit in the peak of summer heat. Having your HVAC technician drop by each spring for an inspection and maintenance call will help keep your unit running reliably all summer long.