How to Test a Capacitor on an Air Conditioner

Capacitors are electrical components that store and release energy. They are an important part of an air conditioning system and are responsible for starting and running the motor that drives the compressor. Over time, capacitors can wear out or become damaged, which can result in a malfunctioning air conditioner. Therefore, it is essential to test capacitors regularly to ensure that they are working correctly. In this article, we will discuss how to test a capacitor on an air conditioner.

What is a Capacitor?

Before we get into how to test a capacitor on an air conditioner, it is essential to understand what a capacitor is and how it works. A capacitor is an electronic component that stores an electric charge. It consists of two metal plates separated by an insulating material called a dielectric. When a voltage is applied to the capacitor, it charges up, and when the voltage is removed, it discharges.

In an air conditioning system, there are two types of capacitors: the run capacitor and the start capacitor. The run capacitor is used to help the compressor run more efficiently, while the start capacitor is used to provide an extra boost of power to help the compressor start up.

Signs of a Bad Capacitor

If your air conditioner is not working correctly, it could be due to a bad capacitor. Here are some signs that your capacitor may be faulty:

  • The air conditioner won’t turn on.
  • The air conditioner turns on but doesn’t blow cold air.
  • The air conditioner makes strange noises, such as humming or buzzing.
  • The air conditioner turns off on its own.

If you notice any of these signs, you should test the capacitor to see if it needs to be replaced.

Tools Needed to Test a Capacitor

To test a capacitor on an air conditioner, you will need a few tools:

  • A digital multimeter
  • A screwdriver
  • A pair of pliers
  • A flashlight (optional)

How to Test a Capacitor on an Air Conditioner

Now that you have the necessary tools let’s discuss how to test a capacitor on an air conditioner.

Step 1: Turn Off the Power

The first step is to turn off the power to the air conditioner. You can do this by turning off the circuit breaker that controls the air conditioner or by unplugging the unit from the wall.

Step 2: Remove the Capacitor

Once the power is off, you can safely remove the capacitor. The capacitor is a cylindrical device with wires attached to it. It is usually located near the compressor. You may need to use a screwdriver to remove the cover that protects the capacitor.

Step 3: Discharge the Capacitor

Before testing the capacitor, you must discharge it to ensure that it is safe to handle. You can do this by using a pair of pliers with insulated handles. Touch the metal ends of the pliers to the two metal terminals on the capacitor at the same time. This will discharge any electrical charge that is stored in the capacitor.

Step 4: Set the Multimeter

Set your multimeter to measure capacitance. If you are not sure how to do this, consult the user manual for your multimeter.

Step 5: Test the Capacitor

To test the capacitor, touch the leads of the multimeter to the terminals on the capacitor. The multimeter should display a reading that is within 10% of the capacitance rating that is printed on the side of the capacitor. For example, if the capacitor has a capacitance rating of 40 microfarads, the multimeter should display a reading between 36 and 44 microfarads.

If the multimeter displays a reading that is significantly higher or lower than the capacitance rating, the capacitor is faulty and needs to be replaced.

Step 6: Test the Capacitor for Charge Retention

In addition to checking the capacitance, you should also test the capacitor for charge retention. This test will determine if the capacitor can hold a charge.

To perform this test, set your multimeter to measure resistance. Touch the leads of the multimeter to the terminals on the capacitor. The multimeter should display a reading that starts at zero and then gradually increases. If the multimeter shows a reading that stays at zero or doesn’t increase, the capacitor has lost its ability to hold a charge and needs to be replaced.

Step 7: Reinstall the Capacitor

Once you have tested the capacitor and determined that it needs to be replaced, you can reinstall the new capacitor. Make sure to connect the wires to the correct terminals.

Step 8: Turn On the Power

After you have reinstalled the capacitor, you can turn the power back on to the air conditioner. Test the air conditioner to ensure that it is working correctly.


Testing a capacitor on an air conditioner is a simple process that can help you avoid costly repairs and keep your air conditioner running efficiently. By following the steps outlined in this article, you can easily test your capacitor and determine if it needs to be replaced. Remember to always turn off the power before testing the capacitor and use caution when handling electrical components. If you are unsure about any of the steps or do not feel comfortable performing the test yourself, it is best to contact a professional HVAC technician for assistance.

See the video For proper Guideline

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