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Troubleshoot

How to Test Contactor on Ac Unit?

ByRalph P. Sita Updated onJanuary 26, 2025

To effectively test a contactor on an AC unit, there are several methods that ensure proper functioning of this critical electrical component. First, using a multimeter is an excellent way to check the continuity of the contactor’s coils, which is essential for determining whether the electrical path is complete. Alternatively, a Continuity Tester can be employed, as it is specifically designed for testing the integrity of electrical components like contactors. Additionally, manually engaging the contacts of the contactor allows you to observe if they close correctly, providing immediate feedback on the component’s operational status. By utilizing these techniques, you can ensure that the contactor in your AC unit is working efficiently.

How to Test Contactor on Ac Unit

Page Contents

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  • How Do I Test My Ac Contactor? – Details with steps
  • How Do You Test a Hvac Contactor With a Multimeter?
  • How to Reset Ac Contactor?
  • Ac Contactor Stuck Closed
  • Ac Contactor Failure Symptoms
    • Related Articles

How Do I Test My Ac Contactor? – Details with steps

First, make sure that there is power going to the unit. You can do this by checking the circuit breaker or fuse box. If the breaker has tripped or the fuse has blown, reset it and see if that fixes the problem.

If there is power to the unit, take a multimeter and set it to Ohms mode. Touch one lead of the multimeter to each of the terminals on the contactor (there should be three). If you get a reading of infinity, that means there is an open circuit and the contactor needs to be replaced.

If you get a reading of zero, that means there is a short circuit and the contactor also needs to be replaced. A reading somewhere in between these two values indicates that the contactor is likely still good but may need some cleaning or adjustment.

How Do You Test a Hvac Contactor With a Multimeter?

First, locate the contactor on your HVAC unit. It will typically be a large rectangular box with wires running into it. Once you’ve found the contactor, open it up and locate the two terminals that are connected to the coil inside.

These terminals will usually be labeled “L” and “N”. Next, take your multimeter and set it to the resistance setting. Touch one probe to each of the terminals on the coil (labeled “L” and “N”).

You should see a reading of around 30 ohms on your multimeter’s display. If you don’t see a reading at all, or if you see a reading that’s significantly higher or lower than 30 ohms, this indicates that there may be an issue with your contactor.

How to Reset Ac Contactor?

In some cases, you may be able to reset the contactor yourself. Here’s how: First, locate the contactor.

It will usually be mounted near the compressor, inside the main electrical panel. Once you’ve found it, open up the panel and look for a small lever or button near the contactor. This is the reset button.

Press and hold the reset button for a few seconds, then release it. You should hear a click as the contacts inside the contactor close. If not, try pressing and holding the button again for a longer period of time.

Once you’ve successfully reset the contactor, close up the electrical panel and turn on your AC unit. It should now work properly.

Ac Contactor Stuck Closed

First, check to make sure that the power is turned off to the unit. If it is, then you’ll need to remove the cover of the contactor so that you can access the contacts. Once you have access, use a wire brush or other similar tool to clean off any buildup on the contacts.

This will help ensure that they make good contact when they’re supposed to. Once you’ve cleaned the contacts, reassemble the contactor and turn on the power to see if it works properly now. If not, then you may need to replace the entire contactor assembly.

Ac Contactor Failure Symptoms

1. The air conditioner won’t turn on.

This is the most obvious symptom of a failed AC contactor. If the contactor has failed, it will no longer be able to engage the air conditioning compressor, and the system will not be able to produce cool air.

2. The air conditioner turns on but doesn’t produce cool air.

If the AC contactor has failed, the compressor may still be engaged but not working properly. This can cause the air conditioner to turn on but not adequately cool your home.

3. Strange noises coming from the air conditioner.

A failing AC contactor can cause strange noises like buzzing or clicking as it tries to engage the compressor. These noises may only happen when you try to turn on the air conditioner or may occur intermittently even when the system is running.

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Ralph P. Sita
Author: Ralph P. Sita

Ralph P. Sita is a seasoned professional with deep roots in both the HVAC and tech industries. His family’s business, Ralph P. Sita, Inc., is a locally owned and operated HVAC contractor with over 42 years of experience, serving the DC, Maryland, and Virginia areas. The company specializes in residential, commercial, and industrial heating, ventilation, and air conditioning services, offering everything from installation and maintenance to custom ductwork and indoor air quality solutions -www.ralphpsita.com. A former CPA, he spent the last decade as co-founder and co-CEO at Cybrary, a leading platform for cybersecurity and IT training. Cybrary became the largest, most well-known cybersecurity training businesses in the industry under his leadership. Smart AC Solutions is an opportunity to give back to the HVAC community by providing reliable, actionable information on all things heating and cooling.

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Ralph P. Sita

Ralph P. Sita is a seasoned professional with deep roots in both the HVAC and tech industries. His family’s business, Ralph P. Sita, Inc., is a locally owned and operated HVAC contractor with over 42 years of experience, serving the DC, Maryland, and Virginia areas. The company specializes in residential, commercial, and industrial heating, ventilation, and air conditioning services, offering everything from installation and maintenance to custom ductwork and indoor air quality solutions -www.ralphpsita.com.

A former CPA, he spent the last decade as co-founder and co-CEO at Cybrary, a leading platform for cybersecurity and IT training. Cybrary became the largest, most well-known cybersecurity training businesses in the industry under his leadership.

Smart AC Solutions is an opportunity to give back to the HVAC community by providing reliable, actionable information on all things heating and cooling.

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