To test the fan motor on your air conditioner, you’ll have to do a continuity test. Click here for a video tutorial. Before you start, make sure the thermostat is set to cool and that the temperature setting is as low as it will go.
Step 1. Check the power
If you suspect the fan motor is bad, the first thing you should check is the power to the motor and the power to the air conditioning unit. Locate the circuit breaker and ensure it hasn’t tripped. If the power is fine, check to see if there is proper voltage. You can do this at the transformer, checking for a fuse in the low-voltage circuit.
Step 2. Check the windings
Next, check the windings of the fan motor for an open or a short. To do this, you’ll have to measure the ohms. If your fan motor is a 120V, it will most likely have four colored wires (black, blue, red, yellow, etc.), as well as a white wire, a black wire, and two brown wires. If you’re working with the wires, do a resistance check between the white wire and each of the colored wires. The higher the resistance is, the lower the speed is, with each colored wire representing a different speed.
Look for a resistance reading. A reading of zero means the fan motor winding is likely shorted and causing the breaker to trip or blow. An infinite reading, on the other hand, may indicate an open motor winding. If either of these conditions exists, the fan motor needs to be replaced.
Step 3. Inspect the capacitor
Keep in mind that just because the fan motor isn’t running, doesn’t mean it’s bad. If the power supply is fine and the windings are in good shape, check the capacitor next.
The capacitor helps the fan motor run. Delivering torque to the fan motor, if the capacitor is faulty, there won’t be enough power delivered and the blower wheel, fan belt, and other important components can cease to operate.
To inspect the capacitor, make sure it is discharged. Once it is discharged, use a capacitor tester to check the microfarad reading. The reading should be within 10 percent of the rated capacitance on the capacitor. If the reading doesn’t match the rating, replace the capacitor.
Contact Person: Ms. Amanda Gu