AC Condenser Fan Motors – What You Need to Know

The AC condenser fan is a critical piece of equipment that helps remove heat from the condenser coil.

While seemingly simple, the AC condenser fan motor is quite complicated—coming in many different horsepower ratings, speeds, and sizes (among many others!)

In this article, I’ll go over how to figure out if your AC condenser fan motor is bad, and how to test your AC condenser fan motor.

I’ll also discuss everything you need to know when purchasing a replacement AC condenser fan motor.

How do you know if your AC condenser fan motor is bad?

Here are a few signs that your AC condenser fan motor is bad:

  • The condenser fan won’t turn on—even when the compressor is running.
  • The condenser fan turns on, but it spins slowly.
  • The condenser fan motor makes a buzzing or other strange noise when it turns on.
  • There is a burning smell coming from your condenser fan motor.

How to troubleshoot an AC condenser fan motor

If you suspect that your AC condenser fan motor is bad, there are a few tests that you can do.

Here are the tests that you’ll need to do to test your AC condenser fan motor:

Check the motor bearings and shaft

The first thing to check on your AC condenser fan motor is its bearings and shaft.

The bearings are responsible for assisting the rotation of the motor. They support the rotor inside of the motor so it spins freely.

Some condenser fan motors need to be oiled periodically to work properly. Without lubrication, the motor’s bearings may wear out or get damaged.

If the bearings get damaged, then the motor won’t spin freely. 

A simple way to test the bearings is to spin the motor shaft by hand. The shaft should spin freely.

If you feel any grinding or inconsistent rotation, then the motor’s bearings are damaged.

If the motor’s bearings are damaged, then the motor needs to be replaced.

Test the motor windings

Testing the condenser fan motor’s windings is a simple test that you can do to figure out if the motor is bad.

In order to do the following tests, you’ll need a multimeter. Switch your multimeter to its resistance (Ohms or Ω) setting.

To test a PSC condenser fan motor, follow the steps below:

  1. Turn off the power to your AC condenser.

  2. Disconnect the motor from the capacitor and contactor. Keep track of the wire connections because you’ll need to rewire them when you’re finished testing.

  3. Take resistance readings between each pair of wires.
    For example, if you have purple, brown, and black wires, take the following resistance readings:

    1. Purple to black
    2. Purple to brown
    3. Black to brown
      Note: If your PSC motor has 4 wires, then you can ignore the 4th wire (usually brown with a white stripe).
  1. Add up the two smaller resistance readings.
    1. If the two smaller resistance readings add up to the larger resistance reading, the motor is good.
    2. If the two smaller resistance readings do not add up to the larger resistance reading, the motor is bad.
    3. For example, if your three resistance readings are 20Ω, 30Ω, and 50Ω, the motor is good because 20 + 30 = 50.

  2. If any of the resistance readings are OL (open line) or short (around 0Ω or 1Ω), then the motor is bad.

Test the motor for shorts

Another test that you can do on your condenser fan motor is to test it for a short to ground. 

When a motor winding shorts to ground, then the motor won’t work.

To test your AC condenser fan motor for a short to ground, follow these steps:

  1. Turn off the power to your AC condenser.

  2. Disconnect the motor from the capacitor and contactor. Keep track of the wire connections because you’ll need to rewire them when you’re finished testing.

  3. Take resistance readings between each wire and the motor housing, one at a time.

  4. If the resistance of any of the motor wires is less than 100 megaohms (MΩ), then the motor is shorted to ground and needs to be replaced.

Test the motor capacitor

In some cases, there might be nothing wrong with the motor itself. The issue might be the motor’s capacitor.

If the motor’s capacitor is bad, then the motor won’t run. There are some rare cases where the motor might run without a capacitor, but the motor will eventually overheat and break.

Most fan motors will run with an improperly sized capacitor, but the motor’s lifespan will decrease. This is because a capacitor that is under- or over-sized will cause your condenser fan motor to overheat. So it’s important that you use a capacitor with the correct rating.

If you have a multimeter with a capacitor tester, then you can test your capacitor to confirm that it is working properly.

To test your motor’s capacitor, follow these steps:

  1. Turn off the power to your AC condenser.

  2. Disconnect the wires connected to the capacitor. Remember where the wires connect to—you’ll have to put them back when you’re done.

  3. Discharge the capacitor by shorting the terminals together with a screwdriver.

  4. Connect your multimeter leads to the “C” and “FAN” terminals on the capacitor.

  5. Turn your multimeter to the capacitance setting (μF, MFD, or capacitor symbol – see below).

  6. Take the capacitor reading. It will be measured in microfarads (μF).

  7. Compare the multimeter’s capacitance reading to the capacitor’s specification. The capacitance reading should be within the capacitor’s specification.

    For example, a capacitor with a rating of 5μF ± 6% should measure between 4.7 and 5.3 μF. If the capacitance does not measure within specification, then the capacitor is bad.
Some multimeters use the capacitor symbol to denote the capacitance testing setting

9 things you need to know when buying a replacement AC condenser fan motor

When purchasing a replacement AC condenser fan motor, there are a few critical pieces of information that you’ll need.

I’ll go over the different specifications that you’ll need to know to get the correct AC condenser fan motor below:

  1. Horsepower
  2. Amperage
  3. RPM
  4. Voltage
  5. Shaft size
  6. Frame size
  7. Number of speeds
  8. Rotation direction
  9. Capacitor rating
AC condenser fan motor specifications

Horsepower

Horsepower is the measurement of how powerful a motor is. The more horsepower that a motor has, the more work that it can perform.

Does horsepower matter on a condenser fan motor?

Yes, horsepower matters on an AC condenser fan motor. The new motor needs to be the same horsepower as the one that you’re replacing.

If the new motor has more horsepower than the old motor, then the new motor will be underloaded. 

If the new motor has less horsepower than the old motor, then the new motor will be overloaded.

Underloading or overloading the motor may cause the motor to overheat and cause electrical trips.

Some folks say that it doesn’t hurt to go with a larger horsepower motor than the one you’re replacing.

For example, swapping a ⅕ HP motor with a ¼ HP motor. While it probably won’t hurt too much, I always like to go with the manufacturer’s specification and use the same horsepower.

Amperage

Amperage is the measurement of how much current the motor consumes. The more current that the motor consumes, the more power it uses.

When replacing an AC condenser fan motor, you’ll need to match the amperage of the new motor to the old motor.

RPM

Rotations per minute, or RPM is the measurement of how fast the motor turns. The higher the RPM, the faster the motor spins.

When replacing an AC condenser fan motor, you’ll need to match the RPM of the new motor to the old motor.

The most common RPMs for AC condenser fan motors are 825 RPM and 1075 RPM.

Voltage

The voltage rating of an electric motor is how much voltage must be provided to the motor for it to run.

For example, a single-phase AC condenser fan motor could have a voltage rating of 208-230 volts. This means that the motor can run on a power source with a voltage of 208 volts or 230 volts (which is nominally 240 volts in most areas).

When replacing an AC condenser fan motor, the voltage of the power source that you’re using needs to match the rating of the motor.

Shaft size

The shaft is the metal rod that protrudes out of the motor. The purpose of the shaft is to transfer the work from the motor to the motor’s load.

Motor shafts come in different diameters and lengths. Most AC condenser fan motors have a ½” shaft diameter.

The shaft length is a whole different story.

If you use a replacement OEM motor when swapping an AC condenser fan motor, the shaft length will be the same size.

However, if you use an aftermarket replacement motor, then the shaft length will be much longer. The motor shaft is longer to accommodate different types of applications. This means that you’ll need to cut down an aftermarket fan motor’s shaft to the correct size.

Another thing you’ll need to do is set the fan blade at the correct height. If you’re using an exact replacement OEM motor, then you can set the fan blade at the same position on the motor shaft.

If you’re using an aftermarket motor, then you’ll need to take a height measurement to figure out where the fan blade needs to be set on the new motor’s shaft. 

Frame size

The motor’s frame is the housing that encloses the motor. Motors for AC condenser fans come in a few different sizes.

The most common frame size for a residential AC condenser fan motor is the 48 frame. The 48 frame measures 5-⅝” in diameter.

Some larger AC condensers may have a fan motor with a 56 frame. The 56 frame measures 6-½” in diameter.

Number of speeds

Most homes have single-stage condensers, so chances are that you only need a regular single-speed condenser fan motor.

However, some AC condensers have multiple stages. If you have a multi-stage condenser, then your condenser fan motor will have multiple speeds.

Most multi-stage condensers have 2 stages, so the condenser fan motor will have 2 speeds—low and high.

Rotation direction

The rotation direction of an AC condenser fan is critical. If the fan motor spins the wrong way, then your AC won’t work.

How do you know which way your AC condenser fan is supposed to spin?

The easiest way to figure out the rotation direction of an AC condenser fan is to look at the fan blades. The fan blades should scoop air up and out of the top of the condenser. 

Motor rotation directions are usually denoted as clockwise (CW) or counter-clockwise (CCW). Most manufacturers indicate the rotation direction when looking at the shaft-end of the motor. 

The easiest way to figure out shaft rotation is to look at the motor’s nameplate. The nameplate usually has an arrow that indicates the direction of rotation of the motor.

Some motors are reversible. This means that you can change the direction of the rotation of the motor. 

Most reversible motors have external connectors that stick out of the motor. If you swap the connectors, the motor will change direction.

Capacitor rating

Most AC condenser fan motors are permanent split capacitor (PSC) motors. PSC motors require a capacitor to run.

The motor will have a rating for the capacitor that needs to be used with it. The rating of the capacitor will be denoted on the motor’s nameplate. For example, a motor may require a 5μF/370V capacitor in order to run.

The microfarad (μF or MF) rating of the capacitor needs to EXACTLY match what is denoted on the motor. However, the voltage rating of the capacitor needs to be AT LEAST what is denoted on the motor.

For example, a 5μF/440V capacitor can be used in place of a 5μF/370V capacitor.

But a 7.5μF/370V capacitor CAN NOT be used in place of a 5μF/370V capacitor.

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