how to change contactor on ac unit



Changing the contactor on your AC unit is a crucial maintenance task that ensures the proper operation and efficiency of your cooling system. The contactor is an electrical component responsible for controlling the flow of electricity to your AC's compressor and condenser fan motor. Over time, contactors can become worn out or damaged, leading to issues such as frequent cycling, failure to start, or even total system shutdown. In this comprehensive guide, we will walk you through the process of changing the contactor on your AC unit, providing step-by-step instructions and valuable tips to help you successfully complete the task.

The Function of a Contactor

A contactor is an electromechanical device that serves as a switch for the electrical current flowing to your AC's compressor and condenser fan motor. It consists of a coil and a set of contacts. When the coil is energized, it creates a magnetic field that pulls the contacts together, allowing electricity to flow. When the coil is de-energized, the contacts separate, interrupting the electrical circuit. This on-off action of the contactor controls the operation of your AC unit, allowing it to cycle on and off as necessary to maintain the desired temperature.

Signs That Your Contactor Needs to be Changed

A malfunctioning contactor can lead to various issues in your AC system. Here are some common signs that indicate it's time to replace the contactor:

1. Frequent Cycling - If you notice your AC unit cycling on and off more frequently than usual, it could be a sign of a faulty contactor. A worn-out contactor may not provide a stable connection, causing the system to turn on and off rapidly.

2. Failure to Start - When you set your thermostat to a lower temperature, but your AC unit fails to start, a defective contactor could be the culprit. A broken contactor may not properly engage and send the electrical current to the compressor and fan motor.

3. System Shutdown - In extreme cases, a completely failed contactor can cause your AC unit to shut down entirely. This occurs when the contacts no longer connect, cutting off the power supply to critical components of the system.

4. Audible Clicking - If you hear a clicking sound coming from your AC unit, especially when it should be running, it could indicate a faulty contactor. The clicking noise is produced when the contactor tries to engage but fails to do so properly.

5. Visual Wear and Tear - Over time, contactors can show signs of wear and tear, such as burnt or pitted contacts, melted plastic insulation, or loose terminals. If you visually inspect your contactor and notice any of these issues, it's a clear indication that it needs to be replaced.

Gather the Necessary Tools and Materials

Before you begin the process of changing the contactor on your AC unit, make sure you have the following tools and materials on hand:

- Screwdriver

- Needle-nose pliers

- Wire cutters/strippers

- Voltage tester

- Replacement contactor (make sure to match the current rating and specifications of your existing contactor)

- Electrical tape or wire nuts

- Safety gloves

- Safety goggles

It's essential to prioritize safety when working with electrical components. Ensure that your AC unit is powered off at the main electrical panel, and consider turning off the circuit breaker or disconnecting the power supply to the unit for an added layer of safety.

Removing the Old Contactor

1. Turn Off the Power

Start by turning off the power supply to your AC unit. Locate the main electrical panel and switch off the circuit breaker that controls the AC's circuit. For extra safety, you may also want to disconnect the power supply at the AC unit itself.

2. Locate the Contactor

The contactor is typically located in the outdoor unit's electrical compartment. Remove the access panel or cover to gain access to the contactor. Use caution as some components may still carry electricity even after powering off.

3. Identify the Wiring

Take a moment to familiarize yourself with the contactor's wiring arrangement. The contactor will have multiple terminals where various wires are connected. Each wire should be labeled for easy identification. Using a voltage tester, ensure that there is no electricity present at the contactor before proceeding.

4. Disconnect the Wires

Using needle-nose pliers, carefully detach the wires from their respective terminals. It's advisable to label each wire using tape or a marker to avoid confusion during the reconnection process. Additionally, take note of the wire colors and their corresponding terminals.

5. Remove the Contactor

Once all the wires are disconnected, you can remove the old contactor. Depending on the AC unit model, it may be secured with screws or clips. Use a screwdriver to remove any screws or release the clips, allowing you to pull the contactor out.

Installing the New Contactor

1. Inspect the New Contactor

Before installing the new contactor, perform a visual inspection to ensure it matches the specifications of the old one. Verify that the voltage rating and current capacity are compatible with your AC unit. Additionally, double-check the arrangement and labeling of the terminals to match your system's wiring.

2. Position the New Contactor

Place the new contactor in the same position where the old one was removed from. Make sure it is properly aligned and secured either with screws or clips, depending on your unit's design.

3. Reconnect the Wires

Referencing your labels and notes from earlier, begin reconnecting the wires to the appropriate terminals on the new contactor. Take care to match the wire colors and ensure they are tightly secured.

4. Secure and Insulate the Wires

After all the wires are reconnected, use electrical tape or wire nuts to secure and insulate the wire connections. This will prevent any accidental contact or electrical arcs.

5. Test the New Contactor

Once you have finished the installation and ensured all connections are secure, it's time to test the new contactor. Turn on the power supply to your AC unit and observe its behavior. The compressor and fan motor should engage smoothly without any issues. If everything is functioning properly, you have successfully replaced the contactor.


In conclusion, changing the contactor on your AC unit is a task that requires careful attention to detail and safety precautions. By following the step-by-step instructions provided in this guide, you can ensure a successful contactor replacement, restoring the proper operation and efficiency of your cooling system. Remember to gather the necessary tools and materials, turn off the power supply, and be cautious when handling electrical components. As always, if you are unsure or uncomfortable performing the task yourself, it's best to consult a professional HVAC technician. Regular maintenance, such as replacing worn-out contactors, will contribute to the longevity and effectiveness of your AC unit.


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