where is the contactor on ac unit


What is a Contactor on an AC Unit?

The contactor plays a crucial role in the functioning of an air conditioning (AC) unit. It is an electrical component responsible for switching the power supply to the various parts of the AC system. Whether you're a homeowner, a technician, or simply interested in understanding how an AC unit works, it's vital to know where the contactor is located in order to diagnose and resolve potential issues effectively.

Understanding the Contactors in an AC Unit

The contactors in an AC unit are essentially high-voltage switches that control the flow of electricity to different components within the system. They are electromechanical devices composed of a coil, stationary contacts, and movable contacts. When the coil is energized, it creates a magnetic field that pulls the movable contacts, allowing electrical current to flow through the stationary contacts.

By design, the contactor is responsible for opening and closing the electrical circuit required to power the compressor, condenser fan motor, and other important parts of the AC unit. This enables the system to work efficiently and maintain a comfortable indoor environment. Now, let's explore where you can locate the contactor in an AC unit.

Finding the Contactor in an AC Unit

The contactor is typically housed inside the electrical compartment of the outdoor unit, also known as the condensing unit. This is the part of the AC system that houses the compressor, condenser coil, fan, and various electrical components, including the contactor. To locate the contactor, follow these steps:

1. Turn off the Power: Before accessing any electrical components, it's crucial to turn off the power to the AC unit. This ensures your safety and prevents any potential electrical shocks.

2. Identify the Outdoor Unit: Locate the outdoor unit of your AC system. This unit usually sits on a concrete pad near the house, and it contains the fan and compressor.

3. Open the Electrical Compartment: Remove the outer cover of the electrical compartment on the side or top of the outdoor unit. This cover is typically held in place by screws or clips.

4. Identify the Contactor: Once the electrical compartment is open, you will see various electrical components, including the contactor. It is a square or rectangular box with multiple wire connections and one or more noticeable coils.

Understanding the Contactors in an AC Unit - Contactor Parts

The contactor is composed of several distinct parts that work together to control the flow of electrical current. Understanding these parts can help in troubleshooting and diagnosing contactor-related issues.

1. Coil: The coil is the part of the contactor that creates a magnetic field when energized. It is responsible for attracting the movable contacts to close the electrical circuit.

2. Stationary Contacts: Also known as the main contacts, these stationary parts act as terminals for the electrical circuit. When the contactor is closed, electrical current flows through these contacts.

3. Movable Contacts: The movable contacts are attracted by the magnetic field created by the energized coil. When the coil pulls them, they connect with the stationary contacts, closing the electrical circuit.

4. Contacts Springs: These springs keep the movable contacts in the open position when the coil is not energized. They provide a spring-like tension for the contacts to separate until the coil magnetically attracts them.

5. Auxiliary Contacts: Some contactors have auxiliary contacts, which are additional contacts that operate independently of the main contacts. They are often used for control signals, safety features, or providing power to other components in the system.

Understanding the various parts of a contactor helps in identifying any issues that may arise from wear and tear, electrical faults, or mechanical failures.

Common Issues with the Contactor on an AC Unit

As an essential electrical component, the contactor can encounter problems over time. Some common issues include:

1. Worn Contacts: Continuous cycles of opening and closing could lead to the wear and tear of the contact points, resulting in poor electrical conductivity. This may cause the contactor to overheat or fail to function properly.

2. Coil Failure: The coil can fail due to factors like electrical surges, overheating, or old age. A faulty coil may prevent the contactor from closing, leading to a lack of power supply to vital system components.

3. Contactor Buzzing: Buzzing sounds coming from the contactor often indicate electrical arcing or problems with voltage supply. This can occur due to loose connections, faulty wiring, or the need for a replacement.

4. Pitting or Burnt Contacts: Over time, contacts can develop pitting or burn marks due to electrical arcing. This can lead to intermittent power supply or complete circuit failure.

Troubleshooting and Resolving Contactors Issues

If you suspect a contactor issue in your AC unit, it's essential to take appropriate troubleshooting steps. Here are a few suggestions:

1. Visual Inspection: Carefully inspect the contactor for any obvious signs of damage, burnt contacts, or loose connections. Ensure the power to the unit is turned off during this inspection.

2. Cleaning the Contacts: If you notice pitting or burn marks on the contacts, carefully clean them using fine-grit sandpaper or contact cleaning solution. This can improve electrical conductivity.

3. Tightening Connections: Check all wire connections to ensure they are secure and tight. Loose connections can lead to voltage drops or arcing, affecting the contactor's performance.

4. Replacing the Contactor: If you've identified a significant issue with the contactor, such as coil failure or burnt contacts, it's recommended to replace the entire contactor. Consult a professional HVAC technician for assistance if needed.

By troubleshooting and resolving contactor issues promptly, you can ensure the efficient operation of your AC unit and potentially avoid more costly repairs later.


The contactor, an electrical component within an AC unit, plays a critical role in controlling the electrical circuit to various system components. It enables the unit to function optimally, ensuring a comfortable indoor environment. By locating the contactor in the outdoor unit and understanding its parts, you can better troubleshoot and resolve potential issues that may arise with this important device. Be attentive to common contactor problems, such as worn contacts, coil failure, buzzing sounds, and pitting or burnt contacts. By taking appropriate troubleshooting steps and seeking professional help when needed, you can maintain the reliability and performance of your AC unit for years to come.


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