how to change a contactor on an ac unit



Changing a contactor on an AC unit is an essential task that HVAC technicians often encounter. The contactor is a crucial component in an air conditioning unit, responsible for controlling the flow of electricity to various parts of the system. Over time, contactors can wear out or become defective, resulting in issues with the operation of the AC unit. Knowing how to identify a faulty contactor and replace it can save you both time and money. In this article, we will guide you through the process of changing a contactor on an AC unit, providing step-by-step instructions and essential tips along the way.

Identifying a Faulty Contactor

Before diving into the process of changing the contactor, it is crucial to be able to identify whether it is indeed the contactor that is causing the issue with your AC unit. Here are a few signs that may indicate a faulty contactor:

1. AC Unit Not Turning On

If your air conditioning unit fails to turn on when you adjust the thermostat, a faulty contactor could be the culprit. The contactor is responsible for supplying power to the compressor and other major components of the AC unit. If it is defective or worn out, it may not be able to make a proper electrical connection, thus preventing the AC unit from starting up.

2. Constant Clicking Sound

A rhythmic clicking sound coming from the AC unit when it is supposed to be running can indicate a problem with the contactor. This clicking sound is usually caused by the contactor rapidly engaging and disengaging due to a faulty internal mechanism. In such cases, it is likely that the contactor needs to be replaced.

3. Partial Cooling or Poor Performance

Another sign of a faulty contactor is when your AC unit is only partially cooling the space or not cooling it at all, despite the unit running. This indicates that the contactor is not effectively transferring power to all the necessary components of the AC system, resulting in decreased performance.

Materials and Tools Required

Now that you've identified the signs of a faulty contactor, let's move on to the materials and tools you'll need to replace it. Before starting any work on your AC unit, ensure you have the following:

1. Replacement Contactor

- It is essential to have a replacement contactor that matches the specifications of your AC unit. Contactors come in various sizes and configurations, so make sure to purchase the correct one for your system.

2. Screwdriver

- A screwdriver will be needed to remove the access panel and detach the wires connected to the contactor. Depending on the unit, you may need either a flathead or a Phillips head screwdriver.

3. Wire Cutter/Stripper

- Since you will be working with electrical connections, having a wire cutter/stripper is necessary to safely remove and strip the insulation from the wires.

4. Insulating Tape

- Insulating tape is used to secure the wires after they have been connected to the new contactor. It helps prevent any potential electrical hazards by insulating exposed wires.

5. Work Gloves and Safety Glasses

- Ensuring your safety is of utmost importance. Wearing work gloves and safety glasses will protect your hands and eyes while working on the AC unit.

Now that we have the necessary materials and tools, let's move on to the step-by-step process of changing a contactor on an AC unit.

Step 1: Turn Off the Power

Before starting any work on your AC unit, it is essential to turn off the power to prevent any electrical accidents. Locate the electrical disconnect switch near the unit or shut off the corresponding circuit breaker in your electrical panel.

Step 2: Remove the Access Panel

Using a screwdriver, remove the screws securing the access panel and carefully take it off. The location of the access panel may vary based on the model and make of your AC unit, so refer to the manufacturer's instructions if needed. Set the screws aside in a safe place for reinstallation later.

Step 3: Identify the Contactor

Once the access panel is removed, locate the contactor. It is usually a black rectangular or square-shaped component with multiple wires attached to it. Take note of the wire connections and their positions to make reconnecting them to the new contactor easier.

Step 4: Disconnect the Wires

Using a screwdriver, carefully loosen the screws holding the wires in place. Take care not to damage or break any of the wires during this process. After loosening the screws, gently pull the wires out from the contactor. It is recommended to take a picture or make a note of the wire connections beforehand, ensuring you have a reference for later reconnection.

Step 5: Remove the Defective Contactor

With the wires disconnected, you can now remove the faulty contactor. Depending on its mounting method, it may be secured to the unit with screws, brackets, or clips. Carefully unscrew or unfasten the contactor from the unit and set it aside.

Step 6: Install the New Contactor

Take the new contactor and position it in the same location where the old one was removed. Ensure it is aligned correctly and secure it using the appropriate screws, brackets, or clips. Confirm that the new contactor is firmly attached.

Step 7: Reconnect the Wires

Referencing the picture or notes you took earlier, reconnect the wires to the new contactor. Insert each wire into the appropriate terminal, making sure they are securely fastened. Tighten the screws to ensure a proper electrical connection. Double-check that each wire is connected to the correct terminal, as incorrect connections can cause further issues.

Step 8: Insulate the Connections

After reconnecting the wires, it is crucial to insulate the connections for safety purposes. Using insulating tape, wrap each wire connection individually to protect them from exposure. Ensure that no bare wires are visible once the insulation is applied.

Step 9: Replace the Access Panel

Carefully reposition the access panel back onto the AC unit and secure it using the screws you set aside earlier. Tighten the screws firmly but avoid overtightening. Ensure the panel is properly aligned and seated, allowing for unrestricted airflow.

Step 10: Restore Power and Test

After completing the installation of the new contactor and securing the access panel, it's time to restore power to your AC unit. Turn on the electrical disconnect switch or switch on the corresponding circuit breaker in your electrical panel. Set the thermostat to a desired temperature and check if the AC unit starts up properly. Listen for any unusual sounds or observe any issues with the performance. If everything appears to be functioning correctly, congratulations! You have successfully changed the contactor on your AC unit.


Changing a contactor on an AC unit is a task that homeowners can tackle themselves, provided they have the necessary tools, materials, and follow the proper steps. By identifying the signs of a faulty contactor and following this comprehensive guide, you can save time and money by completing the replacement yourself. However, if you are not comfortable working with electrical components or encounter any difficulties during the process, it is recommended to seek the assistance of a qualified HVAC technician. Remember, safety is paramount when working with electricity, so always ensure the power is turned off before proceeding with any maintenance or repairs on your AC unit.


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