AC Unit Fan Not Spinning? (Possible Causes & Fixes)

AC Unit Fan Not Spinning

AC problems at the height of summer are never a good situation. When the fan on top of your AC condensing unit fails to spin, it is a symptom of bigger issues requiring immediate attention. Failing to address an AC condenser fan that doesn’t spin can lead to more serious damage to your HVAC system.

In general, an AC condenser fan that doesn’t spin has three possible causes. The start capacitor may be bad, which will prevent the fan motor from starting properly. The fan motor may be bad and need replacement. There is a power problem with the circuit that feeds your AC condensing unit.

No matter the cause of the fan on your C condensing unit not spinning, it is critical to find the problem. You must make these repairs to prevent further and more serious damage to the HVAC system. The three major causes of a condensing unit fan failure are relatively easy to diagnose but usually require the services of a trained HVAC technician.

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What Does the AC Condensing Fan Do?

The AC condensing unit fan does what all fans do. It moves air. Specifically, it moves air across the refrigerant coils and the compressor to keep them cool. As the AC system removes heat from your home, it must go somewhere. As the refrigerant moves through the system, the heat it collects in your home is released back into the atmosphere in the refrigerant coils in your condensing unit.

In addition, as the compressor in the condensing unit compresses the refrigerant, the compressor generates heat. The air movement over and around the compressor helps with cooling and allows the compressor to operate more efficiently.

If the fan on your AC condensing unit doesn’t spin, the air movement over the coils and the compressor isn’t sufficient to adequately cool either one. The AC system begins to operate harder and harder to try and cool your house. Eventually, the compressor or some other part of the AC system will fail.

What Can Cause the AC Fan Not to Spin?

There are several reasons the fan on top of your AC condensing unit doesn’t spin. You may diagnose the problem, but you should call an HVAC technician to make the actual repairs in most situations. The most common reasons for a condensing unit fan not to spin, include:

  • A Bad Capacitor – Most fan motors on condensing units are very efficient as they run. These motors don’t require a lot of electricity to keep the fan turning. However, to get the fan up to speed, the motor must work harder and requires a burst of electricity. The motor starter capacitor provides this surge of electricity when the fan starts. If this capacitor fails, the fan motor won’t be able to start.
  • A Bad Fan Motor – Electric motors, like anything else, can and eventually will fail. These electric motors are subject to constant starts and stops and must operate exposed to the weather. Over time, normal wear and tear will take its toll, and the motor will fail.
  • A Failed Contactor – Inside your AC condensing unit is a contactor. The contactor controls the flow of electricity to the various parts of the condensing unit. If the contactor fails, your condensing unit may not operate, may operate sporadically, or may even operate continuously. In any event, a failed contactor can lead to further damage to your condensing unit. A service call by your HVAC service technician is necessary to have the contactor replaced.
  • Circuit Breaker Problems – Several circuit breakers protect your AC system. Often a dual breaker rated for 240 volts serves the condensing unit while a single 15 amp circuit breaker serves the air handling equipment in the house. Circuit breakers can fail and interrupt or restrict the flow of electricity to your HVAC system. If you suspect that you have problems with your electrical system, including circuit breakers, consult with a licensed electrician to troubleshoot your electrical system.
  • Other Problems – Other problems can cause your HVAC system to operate erratically or not at all. These problems can include a fan on an AC Condensing unit that doesn’t spin. Some of these problems involve bad thermostats or a bad controller board on your HVAC system. Diagnosing these problems is best left to a trained HVAC technician.

How Do I Figure Out What is Wrong with my AC Fan?

There are several methods a homeowner can employ to determine why the fan on an AC condensing unit isn’t working. Some of these methods require more skill than others, and many homeowners may not have the expertise or equipment to do these tests.

A Simple Starting Capacitor Test

If you can hear an audible buzz or hum when your AC system tries to start, more than likely, the starting capacitor on your AC condensing fan is bad. When the fan starts, it needs much more energy than when it is running. Your condensing unit has a starting capacitor to get this extra surge of electrical power. If the capacitor is bad, the fan motor can’t start.

One relatively simple way to test for a bad starting capacity is to start the fan on your condensing unit manually. A manual start is easy don’t but requires care. To perform a manual start on your AC condensing fan, follow these steps.

Step 1: You Need a Tool

The object of this test is to give the blades of your AC fan a push start. Often if the capacitor is bad, providing a push start when the AC unit starts is enough to get the fan turning. You do the job of the capacitor by providing an extra bit of energy.

For this test, an 18 to a 24-inch thin piece of wood is ideal. The wood slat needs to fit between the wire guards over the fan but be strong enough to allow you to give the fan blades a push.

Step 2: Turn on the AC

Turn down your thermostat to get your AC unit started. When you are sure that the AC condensing unit is starting, use the thin piece of wood to give the fan blades a push in the direction they normally turn.

If the capacitor is bad, pushing the fan blades is enough to get the motor started and operating normally. If your AC condensing fan starts to spin after a push, you probably have a bad starting capacitor. Contact your HVAC technician to do further tests and replace the starting capacitor.

Step 3: Turn Off the AC and Call a Service Technician

Turn off the AC at the thermostat. As a precaution, you should also turn off the circuit breaker servicing the condensing unit. Trying to run the AC without the condensing unit fan working properly can damage the compressor and other components of the AC system.

Inspecting the Capacitor

You can also inspect the capacitor for damage. Often, a bad starting capacitor will show signs of damage or failure. These signs include:

  • A swollen or bulging top or sides on the capacitor
  • Leaking fluid from the capacitor
  • Blackened or burned marks around the electrical connections on the capacitor

These signs are often easily visible once you gain access to the capacitor. However, looking at the starting capacitor involves opening the housing on the condensing unit and opening the metal housing that contains the capacitor. A few simple steps will help get a look at the capacitor.

Step 1: Work Safe

Always work safely. Turn off all the circuit breakers that service the AC condensing unit and the HVAC air handling unit. The condensing unit uses dangerous high voltages. The capacitor stores extremely high amounts of electricity and, if the capacitor holds a charge, can deliver a deadly jolt of electricity. Avoid touching anything inside the condensing unit if possible.

Step 2: Open the Condensing Unit

Condensing units from different manufacturers have different methods of accessing the internal parts. Some require removing the entire condensing unit housing, while some have access plates that open to access the electrical parts.

Whatever method your condensing unit employs, be careful as you open the unit. Avoid contacting any wires or cables. Save the screws or bolts and set the housing or panels aside.

Step 3: Access the Capacitor

Typically, the starting capacitor is inside a smaller metal housing. You might notice several bundles of wires running into the box. Carefully open the electrical box and remove the cover.

Step 4: Examine the Capacitor

You may need a flashlight to see the capacitor. The capacitor is usually a round or oval metal can with several electrical connections on top. Don’t touch the capacitor. Visually look for signs of damage on the capacitor. These signs may include swelling or bulging of the capacitor, leaking fluid around the top or bottom of the capacitor, or scorched marks around the electrical connections.

Don’t try to test the capacitor yourself. Contact a qualified service technician to test the system, the capacitor and replace the capacitor if necessary.

Further Testing

Other problems are usually beyond the capacity of most homeowners. The electrical and electronic components of most new HVAC systems require advanced training and diagnostic equipment. Our recommendation is for any homeowner who has problems with their HVAC system to rely on a trained service technician.

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When the Fan on Your AC Doesn’t Spin

When the fan on your AC condensing unit stops spinning, it is time to find the problem before more damage to your AC unit occurs. In most cases, depending on a trained HVAC technician is your best bet. Some homeowners may be qualified to troubleshoot an inoperative fan, but this is generally not the case. Call your HVAC company and schedule a visit by a technician

Dennis Howard

Dennis is a retired firefighter with an extensive background in construction, home improvement, and remodeling. He worked in the trades part-time while serving as an active firefighter. On his retirement, he started a remodeling and home repair business, which he ran for several years.

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