how to replace a contactor on ac unit


How to Replace a Contactor on AC Unit

Is your AC unit acting up? Are you experiencing issues like constant cycling, failure to start, or even no cooling at all? If so, a faulty contactor may very well be the culprit. The contactor is an essential component of your air conditioning system, responsible for controlling the flow of electricity to the unit's compressor and fan motor. Over time, contactors can wear out, become corroded, or fail altogether, resulting in a malfunctioning AC unit. But fear not, replacing a contactor is a relatively simple task that can save you a significant amount of money on professional repairs. In this article, we will guide you through the step-by-step process of replacing a contactor on your AC unit, enabling you to restore comfort and efficient cooling to your home.

Understanding the Contactor

Before we dive into the process of replacing a contactor, it's essential to understand what it is and how it functions. A contactor is an electrical switch that controls the flow of electricity in a circuit. In the case of an air conditioner, the contactor allows the flow of electrical current from the main power supply to the compressor and fan motor. It consists of two sets of contacts, one for the power supply and the other for the motor. When the thermostat signals the need for cooling, the contactor energizes the compressor and fan motor, allowing the necessary electrical current to reach them.

Gathering the Necessary Tools and Equipment

Before you begin the replacement process, it's crucial to gather all the tools and equipment you will need. This preparation will ensure a smooth and efficient replacement process, saving you time and frustration. Here is a list of the items you will require:

1. Screwdriver (Phillips or flathead, depending on your unit's screws)

2. Wire cutters/strippers

3. Insulated gloves

4. Replacement contactor (ensure it matches the specifications of your current contactor)

5. Multimeter

6. Electrical tape

7. Marker or labeling tool

Identifying the Correct Contact Configuration

The first step in replacing a contactor is to identify the correct contact configuration. This information will help you choose the right replacement contactor. Typically, contactors have either a single-pole, double-pole, or triple-pole configuration. To determine the contact configuration, you will need to inspect your current contactor. Look for the number of terminals or wire connections present. A single-pole contactor consists of two terminals, while a double-pole contactor has four terminals. For three-phase units, you will have six terminals, indicating a triple-pole contactor. Take note of this information as you proceed to shop for a replacement contactor.

Turning Off the Power

Before you begin any work on your AC unit, it is of utmost importance to turn off the power to avoid electrical shock. Locate the circuit breaker dedicated to your air conditioning system and switch it off. If you are unsure which breaker controls your AC unit, it is recommended to turn off the main power supply to the entire house. This precautionary step ensures your safety and prevents any accidental power surges while working on the contactor.

Once the power is off, you can proceed with removing the wires from the existing contactor. It's good practice to take a picture or draw a diagram of the current wiring configuration to have a reference during the reinstallation process. This step will help you avoid confusion and ensure that the new contactor is wired correctly.

Removing the Old Contactor

With the power safely turned off, it's time to remove the old contactor. Start by removing the screws or bolts that secure the contactor to the unit's control panel. Place these screws in a safe place to avoid misplacing them during the replacement process. Once the contactor is loose, carefully detach the wires from its terminals. Take note of the wires' positions and labeling if applicable, as this will aid in the reconnection of the new contactor. Remember, some wires may be connected using push-on connectors, while others may require you to loosen terminal screws. Use your wire cutters or strippers as necessary to remove any excess wire or insulation, ensuring a clean and reliable connection.

After removing the old contactor and disconnecting the wires, inspect it for any signs of damage, such as burnt or corroded contacts. This visual examination will help confirm that your old contactor was indeed the source of the problem and validate the need for replacement.

Installing the New Contactor

Now that you have successfully removed the old contactor, it's time to install the new one. Begin by carefully connecting the wires to the corresponding terminals on the replacement contactor. Use your picture or diagram as a guide to ensure correct positioning. It's essential to ensure that each wire is securely fastened and tightly screwed down to prevent any loose connections that could lead to arcing or electrical faults.

Once all the wires are securely connected, position the new contactor in the control panel and secure it with the appropriate screws or bolts. Ensure that the contactor fits snugly and is properly aligned with the mounting holes. This step will prevent any unnecessary vibrations or movement during operation, ensuring the longevity of the contactor.

Before proceeding, it's crucial to verify the correct alignment of the contacts. Manually test the contactor by gently pushing down on the contacts to ensure smooth and controlled movement. If any obstructions or stiff movements are encountered, double-check your installation to address any issues before proceeding.

Double-Checking the Wiring

With the new contactor in place, it's time to double-check the wiring. Carefully review each wire's connection and ensure that they correspond to the correct terminals on the contactor. Take a few moments to reexamine your picture or diagram, ensuring that every wire is correctly positioned and securely fastened. A meticulous review at this stage will prevent any potential electrical malfunctions once the unit is powered back on.

Restoring Power and Testing

Now that the new contactor is installed and the wiring has been verified, it's time to restore power to the AC unit. Locate the dedicated circuit breaker or turn on the main power supply, depending on the precautions you took at the beginning. Once the power is on, head over to your thermostat and set it to the desired cooling temperature. Observe the AC unit to ensure that the contactor engages and the compressor and fan motor kick into action. Take note of any unusual sounds or behaviors that may indicate an issue with the contactor or other components.

It is highly recommended to perform a thorough test of the AC unit's cooling capabilities once the contactor has been replaced. This test will verify that the system is functioning correctly and providing the expected cooling output. Monitor the unit for an extended period to ensure consistent performance and temperature control.


In this article, we have outlined the step-by-step process of replacing a contactor on your AC unit. Understanding the contactor's role and the correct contact configuration is crucial before starting the replacement. Remember to always turn off the power and take caution when removing the old contactor and connecting the wires to the new one. Double-checking the wiring and testing the system before completing the process will help ensure a successful replacement and optimal cooling performance.

Replacing a contactor on your AC unit is a relatively straightforward task, but if you do not feel confident doing it yourself, it is always wise to consult a professional HVAC technician. They have the expertise and experience necessary to diagnose and repair any issues with your air conditioning system. However, if you decide to tackle this project on your own, following the steps outlined in this article will enable you to replace the contactor safely and effectively, allowing you to enjoy a cool and comfortable space during those hot summer months.


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