will faulty contactor cause ac compressor to not run


Will Faulty Contactor Cause AC Compressor to Not Run?


AC compressors are crucial components in air conditioning systems that ensure the proper functioning of the entire unit. However, several factors can hinder the performance of an AC compressor, including a faulty contactor. Contactors are electrical relays responsible for controlling the flow of electricity to the compressor and other crucial components. When a contactor becomes defective, it can lead to the AC compressor not running efficiently or not running at all. In this article, we will explore the potential consequences of a faulty contactor on an AC compressor and discuss troubleshooting techniques to identify if the contactor is indeed the root cause.

How Does an AC Compressor Work?

Before diving into the effects of a faulty contactor on an AC compressor, let's understand the basic functionality of an AC compressor. The AC compressor is responsible for circulating refrigerant within the cooling system, facilitating the heat exchange process. When the thermostat detects a need for cooling, it sends a signal to the air conditioning unit to begin the cooling cycle.

Testing the Contactor:

To determine if a faulty contactor is the reason behind the AC compressor not running, start by switching off the power supply to the unit. Begin the testing process by gently pushing the contactor's manual override button, which is usually located on the side of the contactor. If the contactor engages, the compressor should start running. However, if it fails to respond or exhibits irregular behavior, there is a high probability of a faulty contactor.

Effects of a Faulty Contactor on the AC Compressor:

1. Frequent Compressor Cycling:

One of the primary consequences of a malfunctioning contactor is erratic compressor cycling. A worn-out contactor may cause the compressor to frequently turn on and off, leading to inefficient cooling and increased energy consumption. This continuous cycling puts strain on the compressor motor and can eventually lead to its premature failure, necessitating costly repairs or replacements.

2. Compressor Failure:

A faulty contactor can eventually cause the AC compressor to fail completely. When the contactor fails to send the necessary electrical current to the compressor, it inhibits its ability to function correctly. Over time, this can cause the compressor to overheat and ultimately seize up. Compressor failure often necessitates a complete unit replacement, resulting in significant expenses.

3. Reduced Cooling Capacity:

As the contactor wears out or becomes damaged, it may struggle to provide the proper electrical current needed to power the AC compressor. This can result in reduced cooling capacity, leading to an uncomfortable indoor environment during hot summer months. Additionally, a failing contactor may not activate the compressor consistently, leading to intermittent cooling. This inconsistency can disrupt the comfort of those occupying the space and create an unpleasant living or working environment.

4. Energy Inefficiency:

A faulty contactor can significantly impact the energy efficiency of an air conditioning system. When the contactor is unable to send a strong and consistent electrical current to the compressor, the system may struggle to maintain the desired temperature. As a result, the system works harder and consumes more energy to achieve the same level of cooling. This increased energy consumption leads to higher utility bills and places unnecessary strain on the entire cooling system.

5. Overheating and Electrical Damage:

An unreliable contactor may cause the AC compressor to overheat, potentially resulting in severe electrical damage. When the contactor fails to provide the necessary electrical current or if it is stuck in a closed position, the compressor motor may continue to run without cycling off. This continuous operation puts excessive strain on the motor, potentially causing it to overheat and leading to electrical issues that can impact the entire unit.

Troubleshooting and Resolving Contactor Issues:

1. Inspecting and Cleaning the Contactor:

In some cases, a malfunctioning contactor may not require a complete replacement. Start by inspecting the contactor for any visible signs of damage such as burned or pitted contacts. These signs indicate that the contactor is not functioning correctly and may need replacement. If there are no apparent signs of damage, cleaning the contactor thoroughly with a non-conductive contact cleaner can help remove any dust or debris that might be hindering its performance.

2. Testing the Electrical Current:

To ensure the contactor is receiving the proper amount of voltage, you can use a multimeter to measure the electrical current. Switch off the power supply to the unit and carefully remove the contactor's cover. Place the leads of the multimeter on the contactor's power terminals and check the readings. If the multimeter shows a significantly lower voltage than expected, this indicates a problem with the electrical supply or the contactor itself.

3. Contact a Professional:

If troubleshooting techniques do not resolve the issue, or if you are unsure about performing electrical work, it is recommended to consult a professional HVAC technician. They have the knowledge and experience to diagnose and repair contactor issues accurately. A technician can help identify the root cause of the contactor problem and provide appropriate solutions to get your AC compressor running efficiently again.


A faulty contactor can undeniably cause an AC compressor to not run or run inefficiently. The consequences of a defective contactor include frequent compressor cycling, compressor failure, reduced cooling capacity, energy inefficiency, and the risk of overheating and electrical damage. To troubleshoot contactor issues, inspect and clean the contactor, test the electrical current, and, if necessary, seek professional help.

If you suspect or experience any issues with your AC compressor, it is crucial to address the problem promptly. Regular maintenance and timely repairs can prevent costly replacements and ensure the longevity and efficiency of your air conditioning system. Remember, any electrical work should be performed with the necessary precautions or by a licensed professional to guarantee safety and prevent further damage.


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