how to check the contactor on outside ac unit


How to Check the Contactor on Outside AC Unit


When it comes to your air conditioning unit, the contactor plays a critical role. It is responsible for controlling the flow of electricity to the compressor and condenser fan motor, allowing your AC unit to function properly. Over time, the contactor may wear out or become faulty, resulting in issues with your air conditioner's performance. In this article, we will guide you through the process of checking the contactor on your outside AC unit, enabling you to identify any potential problems and keep your cooling system running smoothly.

What is a Contactor and Why is it Important?

A contactor is an electrical switch that controls the flow of electricity from the power source to the compressor and condenser fan motor in your AC unit. It consists of a set of contacts, which open and close to establish or interrupt the electrical circuit. The contactor is activated by a low-voltage signal from the thermostat, allowing it to control the high-voltage power supply.

The contactor is an essential component of your air conditioning system, as it enables the compressor and condenser fan motor to function. If the contactor fails or malfunctions, it can lead to various issues, including a non-functioning AC unit, erratic cooling, or increased energy consumption. Regularly inspecting and checking the contactor will help you detect any problems early on and ensure your air conditioner operates efficiently.

Signs of a Faulty Contactor

Before we dive into the process of checking the contactor, it's crucial to understand the signs that may indicate a faulty or failing contactor. By recognizing these signs, you can troubleshoot your AC unit effectively:

1. Non-Responsiveness: If your air conditioning unit refuses to turn on or respond to commands from the thermostat, a faulty contactor could be the culprit. The contactor may fail to engage or provide power to the compressor and fan motor, resulting in a non-functioning AC unit.

2. Intermittent Cooling: If you notice that your air conditioner cools the room inconsistently or if the cooling cycle frequently starts and stops, it could indicate a problem with the contactor. Malfunctioning contacts may cause the unit to cycle on and off rapidly, leading to inadequate cooling and increased energy consumption.

3. Loud Clicking Noises: A failing contactor can produce noticeable clicking sounds when it engages or disengages. If you hear these sounds coming from your AC unit, it's advisable to inspect the contactor.

4. AC Unit Stays On: In some cases, a defective contactor can cause the AC unit to stay on continuously, even when the desired temperature has been reached. This constant operation can strain the system and result in higher energy bills.

5. Burnt or Pitted Contacts: If you visually inspect the contactor and notice burnt or pitted contacts, it's a clear sign of wear and tear. Damaged contacts may result in erratic AC performance or failure to start.

How to Check the Contactor:

Now that we understand the importance of the contactor and the signs of a faulty one, let's proceed to the steps for checking the contactor on your outside AC unit. It's important to note that working with electrical components can be dangerous, so if you are not comfortable with electrical systems, it's best to contact a professional HVAC technician.

1. Preparing for Safety: Before starting any work, ensure your AC unit is turned off at the thermostat and the main electrical panel. This will prevent any accidental power supply during the inspection. Additionally, it's advisable to wear safety goggles and gloves for personal protection.

2. Accessing the Contactor: Begin by removing the outer cover of your outside AC unit. In most cases, this involves unscrewing a few bolts or removing clips. Be careful not to damage any fragile components while removing the cover.

3. Locating the Contactor: Once the cover is removed, you should be able to locate the contactor. It is usually a gray or silver-colored box with several electrical terminals and wires connected to it.

4. Visual Inspection: Start by visually inspecting the contactor for any obvious signs of damage or wear. Check for burnt or pitted contacts, as well as loose or disconnected wires. Excessive dirt or debris should also be cleaned.

5. Testing the Contactor: To further evaluate the contactor's functionality, use a multimeter to perform a voltage test. Set the multimeter to the appropriate AC voltage range and carefully touch the leads to the contactor's electrical terminals. The voltage reading should match the specifications provided by the manufacturer.

It's important to remember that working with electrical components poses a risk of electrical shock. If you are uncertain about performing any of the above steps, it's best to seek professional assistance.


Regularly checking the contactor on your outside AC unit is essential for maintaining a well-functioning air conditioning system. By understanding the importance of the contactor and recognizing the signs of a faulty one, you can effectively troubleshoot your AC unit. Be sure to follow safety precautions and, if unsure, consult a professional HVAC technician. By taking care of your contactor, you can enjoy efficient cooling and prolong the lifespan of your air conditioning system.


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