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How To Test Contactor On Ac Unit?




If you’re experiencing issues with your air conditioning unit, one possible culprit could be a faulty contactor.

To test a contactor on an AC unit, follow these steps:

1. Turn off power: Before starting, ensure the power to the AC unit is turned off at the circuit breaker or disconnect switch to avoid any electrical hazards.

2. Locate the contactor: Open the AC unit’s electrical panel and locate the contactor, which is typically a small box with wires connected to it.

3. Visual inspection: Check for any visible signs of damage, such as burnt or melted components, or any debris that may be causing the contactor to malfunction.

4. Check for proper voltage: Use a multimeter to measure the voltage across the contactor’s coil terminals. The reading should be within the contactor’s specified voltage range, typically 24V for residential units. If the voltage is not within the specified range, there may be an issue with the control circuit or transformer.

5. Test coil resistance: With the power still off, disconnect the wires from the contactor’s coil terminals. Set the multimeter to measure resistance (ohms) and place the probes on the coil terminals. The reading should be within the contactor’s specified resistance range, usually a few hundred ohms. If the resistance is too high or too low, the coil may be damaged and the contactor should be replaced.

6. Test contact points: With the power still off, use the multimeter to check for continuity between the contact points when the contactor is engaged. Set the multimeter to measure continuity and place the probes on the contact points. If there is no continuity, the contact points may be damaged or dirty, and the contactor may need to be cleaned or replaced.

7. Test for mechanical issues: Manually press down on the contactor’s plunger to ensure it moves freely and makes proper contact. If it is stuck or does not make proper contact, the contactor may need to be cleaned or replaced.

8. Reconnect wires and restore power: If the contactor passes all tests, reconnect the wires to the coil terminals and restore power to the AC unit. Observe the contactor’s operation during a normal cooling cycle to ensure it is functioning correctly.

If the contactor fails any of these tests or continues to malfunction, it should be replaced by a qualified technician.**

The contactor is responsible for switching the power between the compressor and fan motor, so if it’s not working properly, your AC won’t function correctly.

Learning how to test a contactor on your AC unit can help you diagnose and fix any issues before they become major problems.

Testing a contactor isn’t difficult, but it does require some basic knowledge of electrical systems and safety precautions.

In this article, we’ll walk you through the steps to test a contactor on your AC unit so you can identify any potential problems and fix them quickly.

With our comprehensive guide, you’ll be able to troubleshoot your air conditioning system like a pro and keep it running smoothly all summer long!

Identifying The Contactor

When it comes to testing the contactor on an AC unit, the first step is identifying where it is located.

The contactor is typically found inside the outdoor unit of the air conditioner, usually near the compressor or condenser fan motor.

It’s a small part with a rectangular shape and two sets of terminals.

To locate the contactor, start by turning off power to the unit at the circuit breaker. Once it’s safe to do so, remove the access panel on the outside of the unit.

Look for a small box with wires connected to it; this is likely your contactor.

If you’re not sure which part it is, consult your AC unit manual or contact a professional for guidance.

Equipment Necessary For Testing

Now that you have identified the contactor in your AC unit, it’s time to gather the necessary equipment for testing.

One essential tool you will need is a multimeter, which measures electrical activity and conductivity. You will also need a screwdriver to remove the cover of the AC unit and access the contactor.

Once you have gathered your equipment, it’s time to test the contactor.

Start by turning off the power supply to your AC unit and removing the cover.

Next, locate the contactor and use your screwdriver to remove it from its position.

Use your multimeter to test each terminal on the contactor for continuity by placing one probe on each terminal and checking for a reading on your multimeter.

This will confirm if there is a complete electrical circuit between each terminal.

With these steps, you can effectively test your AC unit’s contactor using simple tools like a multimeter and screwdriver.

Remember to always turn off power before working with electrical components and exercise caution when handling them.

Testing The Contactor

Now that you have located the contactor in your AC unit, it’s time to test it. Imagine yourself as a detective, trying to solve a case.

In this case, your objective is to determine whether the contactor is functioning properly or not.

To begin testing the contactor, use a multimeter to measure the voltage across the contactor’s terminals. If there is no voltage present, then you may have a problem with your thermostat or another component in your AC unit.

However, if voltage is present, then manually push down on the contactor switch to see if it engages with an audible click. If it does not engage, then it may be faulty and require replacement.

Transitioning into troubleshooting steps, if you find that your contactor is faulty and needs replacing, don’t worry! There are several steps you can take to troubleshoot and fix any issues with your AC unit before resorting to replacing parts.

Troubleshooting Steps

Now that we know how to identify a faulty contactor in an AC unit, it’s time to troubleshoot the issue.

Here are some steps you can take to test the contactor:

First, turn off the power supply to the AC unit.

Next, remove the cover of the AC unit and locate the contactor.

Check if there is any visible damage or wear on the contactor’s points.

If you find any, it’s time to replace it with a new one.

Once you have inspected the contactor for visible damage, use a multimeter to test its continuity.

Set your multimeter to ‘ohms’ and touch each lead of the contactor with one probe each.

If there is no reading or an infinite reading, it means that the contactor is bad and needs replacement. On the other hand, if there is a reading between 0-5 ohms, then your contactor is working correctly.

By following these simple steps, you should be able to troubleshoot and test faulty contactors in an AC unit easily.

Remember always to prioritize safety first by turning off power supplies before beginning any inspection or testing work on electrical components of an AC unit.


Overall, testing the contactor on an AC unit is a relatively simple process that can save you time and money in the long run. By identifying the contactor and gathering the necessary equipment, you can quickly test to see if it is working properly.

If it is not, there are a few troubleshooting steps you can take before calling in a professional. One important thing to keep in mind is that safety should be your top priority when dealing with electrical components of any kind.

Always turn off power to the unit before attempting any sort of testing or maintenance.

Additionally, if you are uncomfortable or unsure about anything during the testing process, it’s best to call in a professional rather than risk injury or damage to your AC unit. Ultimately, by taking the time to test your contactor and troubleshoot any issues that arise, you can help ensure that your AC unit is running smoothly and efficiently all summer long.

So don’t hesitate to give it a try – with a little bit of knowledge and practice, anyone can learn how to test their contactor like a pro!

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