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March 30, 2023

How to Test AC Fan Motor: A Brief Guide

Are you having issues with your AC unit? Let Complete Comfort Heating, Air & Plumbing diagnose and fix it when you call (317) 648-5133

The fan motor is an integral component of your air conditioning system: It’s the electrical component that powers your AC unit’s fan. This component works hard under unforgiving conditions for years, so it needs proper maintenance.

Without maintenance, your AC fan motor can fail, causing your air conditioning system’s performance to decline and impacting your home’s comfort. But how do you know that you have a bad fan motor?

As Greenwood’s air conditioning repair experts, the team at Complete Comfort explains how to test an AC fan motor and signs you might have a broken fan motor.

The Main Causes of an AC Fan Motor Failure

While several things can go wrong with an AC fan motor, the most common ones include:

  • Electrical issues: Electrical issues can lead to the motor overheating and burning out, or they can prevent the motor from turning on.
  • Mechanical wear and tear: Regular wear and tear usually damage the fan motor’s bearings and other components. This damage makes it difficult for the motor to rotate.
  • Overheating: If the motor overheats, it can destroy the insulation on the wires, resulting in a short circuit that stops the motor. Dirt and debris build-up on the fan blades is another common cause of fan motor malfunction. 

Over time, contaminants can accumulate and throw the blades off balance. Cleaning your fan blades regularly with a soft cloth or brush can help prevent this issue. Wiring issues are also a common cause of fan motor failure. 

Improper wiring may cause your motor to overheat, damaging its bearings and causing it to stop working. It’s critical to ensure your AC fan’s wiring is in good condition to avoid overheating and permanent damage. 

If you feel your fan motor has problems, don’t hesitate to contact a specialist to check it out and recommend the best solution. Depending on the problem with your AC motor, the specialist may repair or replace the motor. 

With regular maintenance and inspections, you can easily identify fan motor issues and fix them before they cause more severe damage. 

Signs and Symptoms of a Faulty AC Fan Motor 

You’ll find the AC fan in the condenser unit — the part of the air conditioning system parked outside your house. You must go outside to check the fan through the condenser unit’s vents. The common signs that your fan motor is faulty include:

  • The fan doesn’t start even with the AC on. 
  • The fan doesn’t stop even with the AC off
  • The fan turns on, but the blades are rotating slowly
  • A rattling noise comes from the condenser unit when you turn the fan on

These signs can indicate various problems, including defective evaporator coils, so it can be challenging to tell whether the fan motor is the culprit. That’s why it’s important to know how to test an AC fan motor. 

How to Test Your Fan Motor Through a Continuity Test

A continuity test is a simple way to check if your AC fan motor is bad. Before you begin the three-step procedure, set the thermostat to cool and keep the temperature setting as low as possible. 

Step 1: Check the Power

When you suspect you have a faulty fan motor, the first thing to do is check the power to the AC unit and the motor. Check the circuit breaker to ensure that no switch has flipped. 

If you don’t find any unusual issues with the power supply, ensure the voltage is okay by checking for a fuse in the low-voltage circuit at the transformer. 

Step 2: Inspect the Windings

Check the fan motor’s windings for a short by measuring the ohms. A 120-volt fan motor should have four colored wires: two brown wires, a black wire, and a white wire. 

You’ll need to measure the resistance between the white wire and each of the colored wires. A higher resistance translates to a lower speed, and each colored wire represents a different speed.  

A resistance reading of zero indicates a shorted fan motor winding, causing the circuit breaker to blow or trip. An infinite reading often signifies an open fan motor winding. If you confirm any of these issues, consider replacing your AC fan motor.

Step 3: Examine the Capacitor

Simply because your AC fan motor isn’t running doesn’t mean it’s faulty. If you’ve checked the power supply and the windings and everything is fine, the capacitor could be the problem. The capacitor delivers torque to the motor, helping it run. 

A faulty capacity won’t deliver adequate power, and the fan belt, blower wheel, and other critical components can stop operating. Ensure the capacitor is discharged before inspecting it. You can then check the microfarad reading using a capacitor tester. 

Make sure the reading is within 10% of the capacitor’s rated capacitance. Consider replacing the capacity if the reading doesn’t match the rating. 

How to Test AC Fan Motor with a Multimeter

You can also test your fan motor quickly with a multimeter. Follow the simple steps below to determine if your fan motor is functioning efficiently:

  • Turn off the power to the AC unit before testing the motor. 
  • Ensure the multimeter is in the ohm setting. Next, touch probes to the two motor terminals. 
  • An infinite multimeter reading indicates an open circuit, meaning your motor is faulty. 
  • A zero reading signifies a short circuit and the fan motor is faulty. 
  • If the multimeter reading falls between zero and infinite, your fan motor is working properly. 

Give Complete Comfort Heating, Air & Plumbing a Call Today

Now that you know how to test your AC fan motor, it’s best to call a professional when you suspect the motor needs repair or replacement. Complete Comfort Heating, Air & Plumbing is the trusted contractor for all your air conditioning needs in Indianapolis and the surrounding areas. 

Call us at (317) 648-5133 to schedule a professional AC fan motor replacement service or learn why your air conditioner won’t stop running

Author Bio:

Brittany Katterjohn

Brittany is a marketer, entrepreneur, and writer with previous business development experience in the home maintenance industry. She currently manages the marketing for Complete Comfort Heating, Air & Plumbing and has a passion for helping people by simplifying seemingly complicated topics related to home maintenance and repair.

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