how to replace a contactor on an ac unit



Replacing a contactor on an AC unit is a task that may seem daunting to some, but with the right knowledge and step-by-step guidance, it can be a fairly straightforward process. The contactor plays a crucial role in the operation of an air conditioning unit by controlling the flow of electricity to various components. Over time, contactors can wear out or become faulty, leading to issues such as the AC not turning on or inadequate cooling. In this article, we will guide you through the process of replacing a contactor on an AC unit, ensuring that your air conditioner runs efficiently once again.

Understanding the Contactor

The contactor is essentially a large relay that controls the flow of electricity to the compressor, condenser fan motor, and other components of the AC unit. It consists of a coil, contacts, and a housing. When the thermostat signals the need for cooling, the coil is energized, which causes the contacts to close, allowing electricity to flow to the necessary components.

Over time, the contacts can become pitted, worn out, or stuck, impairing the flow of electricity and rendering the AC unit ineffective. Additionally, contactors can sometimes develop defects in their coils, leading to malfunctioning or erratic behavior. Replacing a faulty contactor can help restore proper functioning to your AC unit.

Tools and Materials Required

Before you begin replacing the contactor, it is essential to gather the necessary tools and materials. Here's a list of what you'll need:

1. Screwdriver (Phillips and flathead)

2. Pliers (needle-nose and/or regular)

3. Wire strippers

4. Electrical tape

5. Replacement contactor (make sure to get the appropriate one for your AC unit)

6. Disposable gloves (for safety)

Removing Power and Ensuring Safety

Safety should always be a top priority when working with electrical components. It is crucial to turn off the power supply to the AC unit before attempting any repairs or replacements. Follow these steps to ensure a safe working environment:

1. Locate the electrical panel or breaker box for your AC unit.

2. Identify the circuit breaker that controls the power supply to the AC unit.

3. Switch off the corresponding circuit breaker.

4. Verify that the power has been successfully turned off by attempting to switch on the AC unit. It should not activate.

Taking these precautions will protect you from potential electric shocks and ensure a safe working environment while replacing the contactor.

Disconnecting the Old Contactor

Once you have taken the necessary safety measures, you are ready to proceed with replacing the old contactor. Follow these steps to disconnect the faulty contactor:

1. Locate the contactor inside the AC unit. It is typically found near the compressor unit or in the electrical panel compartment.

2. Carefully inspect the contactor and surrounding wires, taking note of their arrangement and connections. You may want to take pictures for reference later.

3. Using a screwdriver, loosen the screws or bolts securing the wires to the contactor's terminals. Make sure to keep the wires intact and avoid bending or damaging them.

4. Once the wires are detached, take note of their positions. Some contactors have color-coded or labeled terminals to help with reinstallation.

5. Next, use a screwdriver or pliers to remove the screws or fasteners holding the contactor in place. Gently lift the contactor out of its housing, making sure not to disturb any other components.

By following these steps, you have successfully removed the old contactor from your AC unit. Now, let's move on to installing the new contactor.

Installing the New Contactor

Proper installation of the new contactor is vital to ensure the AC unit's optimal functioning. Let's go through the steps to successfully install the replacement contactor:

1. Take the new contactor out of its packaging and compare it with the old one. Ensure that it is an exact match in terms of specifications and terminal arrangements.

2. Carefully position the new contactor inside the housing, aligning it with the screw holes or fasteners from the previous contactor.

3. Secure the contactor in place by using a screwdriver or pliers to tighten the screws or fasteners. Ensure that the contactor is firmly attached and won't shift during operation.

4. Refer to your pictures or notes from earlier to reconnect the wires to their appropriate terminals. If the contactor has labeled or color-coded terminals, follow those guidelines.

5. Gently tighten the screws or bolts to secure the wires in place. Make sure all connections are secure and snug, but avoid overtightening.

6. Inspect the surrounding area to ensure no other wires or components were dislodged during the process.

Congratulations! You have successfully installed the new contactor in your AC unit. Now, let's move on to the final steps to ensure everything is in order before restoring power.

Performing Final Checks

Before turning the power back on and testing the AC unit, it is essential to perform a few final checks to ensure everything is set up correctly:

1. Double-check all your wire connections to ensure none are loose or improperly attached. A loose connection can lead to complications or even damage other components.

2. Inspect the contactor visually, ensuring all wires are securely attached and positioned correctly. Take note of any abnormal or loose connections.

3. Carefully examine the area surrounding the contactor for any signs of damage or areas that may need additional attention. Fix any issues before proceeding.

4. Once you are satisfied with the installation and connections, carefully close the AC unit's electrical panel or compartment.

5. Return to the electrical panel or breaker box for your AC unit and locate the circuit breaker that controls its power supply.

6. Flip the circuit breaker back to the "on" position, restoring power to the AC unit.

With these final checks complete, you are now ready to turn on your AC unit and test its functionality. Monitor the unit for a few minutes, ensuring that it turns on smoothly, and all components are functioning correctly.


Replacing a contactor on an AC unit can be a relatively simple task if done correctly. By following the steps outlined in this guide, you can successfully replace a faulty contactor and restore your AC unit's optimal performance. Remember to always prioritize safety by disconnecting the power supply and taking necessary precautions when working with electrical components. With a new contactor in place, your AC unit will be back to cooling your space effectively and efficiently.


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