how do you test an ac contactor



An AC contactor is a critical component in an air conditioning system and plays a vital role in controlling the flow of electricity. Given its importance, it is crucial to test an AC contactor regularly to ensure it is functioning correctly. This article will guide you through the process of testing an AC contactor and provide you with essential tips to keep your system running smoothly.

Why is Testing an AC Contactor Important?

The AC contactor is responsible for switching the power supply to the compressor and condenser fan motor. Over time, due to wear and tear, the contactor may develop faults, leading to a malfunctioning air conditioning system. By regularly testing the AC contactor, you can identify any issues early on and take proactive measures to avoid any potential system failures.

Tips Before Testing an AC Contactor

Before proceeding with the testing process, it is essential to take certain precautions to ensure your safety and the safety of the equipment. Here are a few tips to keep in mind:

1. Ensure Safety First

Safety should always be your top priority when dealing with electrical components. Turn off the power supply to the air conditioning unit at the main electrical panel before starting the testing process. This will protect you from accidental electric shocks and prevent damage to the equipment.

2. Gather the Right Tools

To test an AC contactor efficiently, you will need a few tools to assist you along the way. These may include a multimeter, insulated gloves, safety goggles, and a screwdriver. Make sure you have all the necessary tools before proceeding with the testing.

3. Understand the AC Contactor

It is crucial to have a basic understanding of how an AC contactor functions before testing it. Familiarize yourself with its components and their respective roles. This knowledge will help you identify any abnormalities during the testing process.

The Testing Process

Now that we have covered the necessary precautions let's delve into the step-by-step process of testing an AC contactor.

1. Locate the AC Contactor

The AC contactor is typically located inside the air conditioning condensing unit. This unit can be found outside the building and houses the compressor, condenser fan, and the contactor itself. Open the access panel of the condensing unit to gain access to the contactor.

2. Inspect for Physical Damage

Before performing any electrical tests, visually inspect the AC contactor for any signs of physical damage or wear. Look out for melted plastic, burn marks, loose connections, or any other abnormalities. If you notice any such issues, it is advisable to replace the contactor rather than testing it.

3. Check for Power Supply

To ensure safety, double-check that the power supply to the air conditioning unit is turned off. Use a multimeter to confirm that there is no voltage present at the contactor. Follow the manufacturer's instructions for the multimeter to accurately measure the voltage. If voltage is detected, do not proceed with the testing process and seek professional assistance.

4. Test for Coil Continuity

The coil is an integral part of the AC contactor and is responsible for closing or opening the contacts. Use the continuity function on your multimeter to test if the coil is functioning correctly. Start by disconnecting the wires from the coil. Place the multimeter probes on the coil terminals and check for continuity. If there is no continuity, it indicates a faulty coil that needs replacement.

5. Examine the Contacts

The contacts of the AC contactor are responsible for allowing or interrupting the flow of electricity. Inspect the contacts for any signs of wear, excessive pitting, or burning. If the contacts appear damaged, replacing the contactor is recommended. However, if the contacts seem intact, proceed to the next step.

6. Test for Contact Functionality

To test the contact functionality, reconnect the coil wires and restore power to the air conditioning unit. Use an insulated screwdriver to manually push the contactor's contacts closed. The contacts should make a firm connection, creating an audible click sound. If the contacts fail to close properly or make a weak connection, it indicates a faulty contactor that needs to be replaced.

7. Inspect for Welded Contacts

In some cases, the contacts may become welded together, causing a continuous flow of electricity even when the contactor should be open. This can lead to various issues, including excessive heat and compressor failure. Use your multimeter to test for continuity across the contacts when the coil is not energized. If continuity is detected, it indicates welded contacts and necessitates replacing the contactor.


Regularly testing an AC contactor is essential for maintaining the efficiency and longevity of your air conditioning system. By following the step-by-step process mentioned above, you can identify any faults in the contactor and take appropriate action, ensuring the smooth functioning of the system. Remember always to prioritize safety when dealing with electrical components, and if any issue seems beyond your expertise, consult a professional to avoid further damage. Keep your AC contactor in good condition, and enjoy the cool comfort it provides.


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