AC Maintenance Tips: How To Troubleshoot an AC Fan Motor

What’s that sound?

Your AC unit is rattling when the fan is on? You still hear the fan after the AC unit has been turned off? Or maybe there’s no sound at all because the fan isn’t coming on.

Whatever the case, it sounds like it is time for some AC maintenance. With summer right around the corner, you don’t want to be left without a working AC unit.

Read on to learn how to troubleshoot a faulty AC fan motor.

Thermostat, Breakers, and Power

Check to ensure that the thermostat is on and set to the correct temperature. Someone may have bumped the thermostat and knocked it out of whack. It sounds silly, but it’s often the culprit.

Also, check the breaker. An AC unit will normally be on its own circuit, so if the breaker is tripped the unit will be the only thing not working.

You can also do a resistance check on the windings of the fan motor. There may be a short or an open that is preventing power from getting to the motor.

Measure the ohms between the white wire and each of the colored wires. Zero indicates a short and an infinite reading indicates an open. In either case, you’ll need a new fan motor.

Clean Filters?

You should change your AC air filters regularly. After a winter of disuse, you may have forgotten that the filter is dirty. This can inhibit the performance of the AC unit.

If you find that the filters are clogged, the fan may not even be the problem.

Check the Fan Blades

If the unit is still having troubles, it’s time to physically check the fan. Debris may be in the way, inhibiting the fan’s ability to operate.

With the AC unit off, use a screwdriver to push the blades and see if they can rotate freely. Once they are moving freely, try turning the unit back on and go back and see if the fan has started up again.

If you give the blades a push with your screwdriver and it starts working, then there is something wrong with the capacitor — not the fan motor.

Inspect the Capacitor

If you’ve checked all of the above and it seems to be in good shape, the problem may lie with the capacitor. This is the component that delivers the necessary torque to the fan motor.

The fan motor may be completely fine but won’t work if the capacitor is bad.

Discharge the capacitor before taking a microfarad reading with a capacitor tester. On the capacitor you’ll find the rated capacitance it should have. If the reading is more than 10% off, you’re going to need a new capacitor.

AC Maintenance From the Pros

The first couple of steps in this troubleshooting guide shouldn’t be too difficult for the average homeowner. But if you find a problem with the fan motor, or suspect an issue with the capacitor it’s time to call in the professionals.

Here at Ellsworth Air, we have expert technicians who will figure out what’s wrong with your AC unit in no time. AC maintenance has never been so easy or convenient!