how to test contactor on ac unit


The Importance of Testing the Contactor on Your AC Unit


The contactor is a crucial component of your air conditioning (AC) unit that plays a significant role in its functionality. Over time, the contactor can wear out or become faulty, resulting in various issues with your AC unit. Therefore, it is essential to regularly test the contactor to ensure optimal performance and prevent any potential problems. In this article, we will guide you through the process of testing the contactor on your AC unit, helping you diagnose any issues and take appropriate measures to resolve them. Let's dive in and learn how to keep your AC unit operating at its best!

Common Signs of a Faulty Contactor:

Before we delve into the testing process, it is crucial to familiarize ourselves with the common signs of a faulty contactor. This knowledge will enable you to identify any potential issues with your AC unit and determine whether testing the contactor is necessary.

1. Irregular Cooling: One of the first signs that your contactor may be faulty is inconsistent cooling. If you notice that your AC unit is not cooling your home as efficiently as it used to or if some rooms are warmer than others, this could indicate a malfunctioning contactor.

2. Unresponsive AC: Another indicator of a faulty contactor is an air conditioner that fails to turn on or respond to your thermostat settings. If you are experiencing difficulties starting your AC unit or if it randomly shuts off, the contactor might be the culprit.

3. Clicking Noises: Faulty contactors often emit clicking or buzzing noises when attempting to power on the AC unit. These sounds indicate that the contactor is struggling to engage or disengage properly, which affects the overall functionality of your AC system.

4. Electrical Issues: In some cases, a malfunctioning contactor can lead to electrical problems. If you notice flickering lights or experience electrical surges when your AC unit is operating, it is essential to investigate the contactor as a potential source of these issues.

Testing the Contactor on Your AC Unit:

Now that you are familiar with the common signs of a faulty contactor, let's move on to the process of testing it. It is important to note that working with electrical components can be dangerous, so it is advisable to follow all safety precautions or consult with a professional if you are unsure.

1. Gather the Necessary Tools and Equipment: Before beginning the testing process, gather the required tools and equipment. You will typically need a multimeter, a voltage tester, insulated gloves, and safety goggles to ensure a safe and accurate testing process.

2. Turn Off the Power: To ensure your safety, locate the electrical panel in your home and turn off the power to your AC unit. This step is vital to prevent any accidental electrical shocks while testing the contactor.

3. Access the Contactor: Once the power is off, you can safely access the contactor. Start by removing the outer access panel of your AC unit. Depending on the model, you may need to unscrew or lift the panel to reach the contactor.

4. Inspect the Contactor: Before testing, conduct a visual inspection of the contactor. Look for any signs of burning, damage, or loose connections. If you notice any significant issues during this inspection, it may be best to replace the contactor entirely.

5. Perform a Voltage Test: Now it's time to test the contactor using a multimeter or voltage tester. Ensure that your multimeter is set to measure voltage and carefully touch the leads to the contactor's terminals. The multimeter should display the voltage reading, confirming whether the contactor is receiving power.

6. Check for Continuity: To ensure the contactor is functioning correctly, you can also test for continuity. Set your multimeter to the continuity or ohms setting and touch the leads to different sets of terminals on the contactor. If there is continuity, the multimeter will emit a beep or display a reading, indicating that the contactor is in good condition.

7. Observe the Coil: The contactor's coil is another crucial component that should be tested. Using the multimeter, set it to continuity or ohms and touch the leads to both sides of the coil. A reading or beep indicates that the coil is intact and operational.

8. Replace the Contactor if Necessary: If any of the tests indicate a faulty contactor, it is advisable to replace it promptly. A malfunctioning contactor can lead to further damage to your AC unit and potentially compromise your safety.


Regularly testing the contactor on your AC unit is vital to maintain its optimal performance and prevent any potential malfunctions. By familiarizing yourself with the common signs of a faulty contactor and following the testing procedures outlined in this article, you can diagnose any issues and take the necessary steps to resolve them. However, if you are uncomfortable or unsure about testing electrical components, it is always best to consult with a professional HVAC technician. Remember, your safety should be the top priority when working with electrical systems. Ensure that you take all necessary precautions and rely on qualified professionals when in doubt. Keep your AC unit in peak condition, and enjoy the comfort it provides year-round!


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