how to test a contactor on ac unit


Why Testing a Contactor on Your AC Unit is Important

Do you rely on your air conditioning unit to keep your home cool during the scorching summer months? If so, it's essential to ensure that all the components of your AC system are in proper working order. One crucial component to test regularly is the contactor. The contactor plays a vital role in the functionality of your AC unit, as it is responsible for controlling the flow of electricity to the compressor and the condenser fan motor. By regularly testing your contactor, you can identify any issues early on and avoid potential breakdowns when you need your AC the most. In this article, we will guide you through the process of testing a contactor on your AC unit, step by step.

What is a Contactor and How Does It Work?

A contactor is an electrical switch that controls the flow of electricity in an HVAC system. Specifically, in an air conditioning unit, the contactor manages the electrical current between the main power supply and the compressor and condenser fan motor. It consists of a coil, which controls the contacts, and the contacts themselves. When the coil is energized, it creates a magnetic field that attracts the contacts, closing the circuit and allowing the current to flow. Conversely, when the coil is de-energized, the contacts open, interrupting the electrical flow. This simple mechanism is fundamental to the functioning of your AC unit, and any issues with the contactor can lead to system malfunction or failure.

Why Should You Test Your Contactor?

Regularly testing your contactor is crucial for several reasons. First and foremost, it helps ensure that your AC unit operates at its optimal efficiency. A faulty contactor can cause your system to overheat or underperform, leading to increased energy consumption and decreased cooling capacity. By testing the contactor, you can identify any problems and address them promptly, thus preventing bigger issues down the line.

Another reason to test your contactor is to minimize the risk of sudden breakdowns. Imagine the discomfort and inconvenience of your AC unit failing on a scorching summer day. By testing the contactor regularly, you can catch any abnormalities or signs of wear and tear before they develop into serious problems. This proactive approach can save you from discomfort and expensive emergency repairs.

How to Test a Contactor on Your AC Unit

Now that you understand the importance of testing your contactor, let's dive into the step-by-step process of carrying out the test. Always remember to prioritize safety when working with electrical components. Before you begin, make sure to turn off the power to your AC unit at the circuit breaker to prevent the risk of electric shock. Here's how you can test your contactor effectively:

Gather the Necessary Tools

Before you begin testing your contactor, gather the following tools:

1. Screwdriver: You will need this tool to remove the access panel and gain access to the contactor.

2. Multimeter: A multimeter is essential in measuring electrical current, voltage, and resistance. Make sure it is set to the appropriate settings for the test.

3. Insulated gloves: Wearing insulated gloves will provide an extra layer of protection while you work with electrical components.

Step 1: Switch Off the Power

As mentioned earlier, turn off the power to your AC unit at the circuit breaker. This step is crucial to ensure your safety while working with electrical components.

Step 2: Locate the Contactor

Remove the access panel on your AC unit to locate the contactor. The contactor is a rectangular or cylindrical device typically located near the compressor. It will have multiple wires attached to it.

Step 3: Inspect the Contactor

Once you have located the contactor, visually inspect it for any signs of damage or wear. Look out for melted plastic, burned wires, or visible corrosion. If you notice any of these issues, it indicates a faulty contactor that needs to be replaced.

Step 4: Test for Power

Put on your insulated gloves and use the multimeter to test for power. Set the multimeter to the appropriate voltage setting, usually 240 volts. Carefully touch the multimeter probes to the main power connections on the contactor. The multimeter should display a reading close to the voltage of your electrical supply. If there is no power or a significantly lower reading, it indicates an issue with the power supply or contactor.

Step 5: Test the Contacts

To test the contacts, use the screwdriver to gently push down on the contacts while the power is still off. As you press down, listen for a click sound, indicating that the contacts are engaging properly. If you don't hear a click or notice any resistance, it suggests a faulty contactor that needs to be replaced.

Step 6: Test the Coil

Turn on the power to your AC unit at the circuit breaker and set the thermostat to call for cooling. With the insulated gloves on, observe the contactor as it energizes. You should hear a distinct humming sound as the coil activates the contacts. If you don't hear any sound or the contacts do not engage, it signifies a problem with the coil.

Step 7: Check for Proper Functionality

Lastly, once you have completed the previous steps, turn off the power again and carefully reassemble the access panel. Switch on the power at the circuit breaker and set the thermostat to call for cooling. Observe the contactor to ensure that it engages and disengages properly, allowing the electrical current to flow smoothly.


Ensuring that your contactor is in proper working order is crucial for maintaining the efficiency and reliability of your AC unit. By regularly testing your contactor, you can identify any issues early on and prevent major breakdowns. Remember to prioritize safety at all times, turning off the power before carrying out any tests and wearing insulated gloves when necessary. By following the step-by-step testing process outlined in this article, you can confidently assess the condition of your contactor and take appropriate action if needed. So, don't neglect this essential maintenance task and keep your AC unit running smoothly all summer long.


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