how do i know if my ac contactor is bad


How Do I Know if My AC Contactor is Bad?

If you're experiencing issues with your air conditioning unit, one potential culprit could be a faulty AC contactor. The AC contactor is an essential part of your system, responsible for controlling the electrical current that flows to the compressor and the condenser fan motor. Over time, the contactor can wear out or become damaged, leading to various problems. In this article, we will explore how you can determine if your AC contactor is indeed the cause of your AC troubles and what steps you should take to address the issue.

What is an AC Contactor?

Before we dive into troubleshooting, let's first understand what an AC contactor is and how it functions. An AC contactor is an electrical switch used in air conditioning units to control the power supply to critical components such as the compressor and the condenser fan motor. It serves as a connecting bridge between the control panel and the high-voltage power source.

The contactor consists of a coil, contacts, and a set of terminals. When the thermostat signals the air conditioner to cool the room, the contactor's coil is energized, causing the contacts to close and complete the electrical circuit. This, in turn, allows the electrical current to flow to the compressor and the condenser fan motor, starting the cooling process.

Signs of a Bad AC Contactor

Identifying a faulty AC contactor can be tricky, as the symptoms can sometimes overlap with other air conditioning issues. However, there are specific signs that indicate a potential problem with the contactor. Here are some common symptoms that may indicate your AC contactor is bad:

1. AC Not Turning On or Off

If your air conditioner fails to turn on or off when it should, it could be a sign of a faulty contactor. When the contactor's coil is damaged or worn out, it may not receive the electrical signal from the thermostat, preventing the contacts from closing or opening as required.

2. Constant Clicking Sounds

A clicking sound that persists even when your AC is not running could indicate a defective contactor. This clicking noise typically comes from the contactor rapidly opening and closing due to a malfunction in the coil or the contacts.

3. AC Runs Intermittently

If your air conditioner frequently cycles on and off without reaching the desired temperature, a malfunctioning contactor may be to blame. When the contactor wears out, it can cause the electrical connection to become unstable, resulting in inconsistent operation of the compressor and the fan motor.

4. Visible Signs of Damage

Inspecting the contactor can sometimes reveal visible signs of damage or wear. Look for melted spots, burnt marks, or corrosion on the contacts or the coil. Any physical damage can affect the performance and reliability of the contactor.

5. High Energy Bills

A malfunctioning contactor can also lead to increased energy consumption and higher electricity bills. If the contactor is stuck in an open position, your AC system may keep running even when it's not necessary, wasting energy and driving up your monthly expenses.

Troubleshooting a Bad AC Contactor

If you suspect your AC contactor is faulty based on the symptoms mentioned above, you can perform some troubleshooting steps to verify the issue before seeking professional help. Here's what you can do:

1. Cut Off Power Supply

Before working on any electrical component, it's crucial to ensure your safety. Locate the circuit breaker panel and turn off the power supply to your air conditioning unit.

2. Inspect the Contactor

Carefully remove the cover of the contactor box to expose the contactor inside. Visually inspect the contacts and the coil for any signs of damage, such as corrosion, burning, or melting. If you notice any visible issues, it's highly likely that your contactor needs to be replaced.

3. Test the Contactor

To test the contactor's functionality, you'll need a multimeter. Set the multimeter to "Ohms" and touch the probes to the contactor's load terminals. If the multimeter shows a reading of zero or infinite resistance, it indicates a faulty contactor that needs to be replaced.

4. Check the Power Supply

Sometimes, the problem may not lie with the contactor itself but rather with the power supply. Inspect the wiring connections and ensure there are no loose or damaged wires. Additionally, check the circuit breaker to ensure it hasn't tripped or that the fuse hasn't blown.

Replacing an AC Contactor

If your troubleshooting confirms that the AC contactor is indeed bad, it's necessary to replace it with a new one. Here's a step-by-step guide on how to replace an AC contactor:

1. Purchase a Compatible Replacement

Identify the model number of your existing contactor and purchase a replacement that matches the specifications. It's crucial to use a compatible contactor to ensure proper functioning of your air conditioning unit.

2. Cut Off Power Supply

As mentioned earlier, turn off the power supply to your air conditioner by switching off the corresponding circuit breaker in the circuit breaker panel.

3. Remove the Old Contactor

Using a screwdriver, carefully remove the screws that secure the contactor to the air conditioning unit. Take note of the wiring connections on the old contactor and take photos if necessary to ensure correct reinstallation.

4. Install the New Contactor

Attach the new contactor in place of the old one, using the same screw holes. Connect the wires according to your reference photos or the wiring diagram provided with the replacement contactor. Ensure all connections are tight and secure.

5. Test the AC Unit

Once the new contactor is installed, switch on the power supply and test your air conditioning unit. Verify that the AC turns on and off properly, and there are no unusual sounds or other issues.


In conclusion, a faulty AC contactor can significantly affect the performance and functionality of your air conditioning unit. Identifying signs of a bad contactor and knowing how to troubleshoot and replace it can save you from enduring hot and uncomfortable conditions. Remember to prioritize safety and consider seeking professional assistance if you're unsure about performing any electrical work. Regular maintenance of your HVAC system can also help prevent contactor issues and ensure the longevity of your air conditioner.


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