what causes ac contactor to go bad


Why Do AC Contactors Go Bad?

Have you ever experienced issues with your air conditioning system suddenly shutting down? Or perhaps you've noticed unusual noises coming from the electrical panel. If so, there's a good chance that a faulty AC contactor could be the underlying cause. The AC contactor is a crucial component of your air conditioning unit, responsible for connecting and disconnecting the power supply to the compressor and condenser fan motor. When this component fails, your AC system may stop functioning altogether, leaving you in discomfort during those sweltering summer months. In this article, we will explore the various reasons why AC contactors go bad and how you can prevent such issues from occurring.

Understanding the Role of an AC Contactor

Before we delve into the causes of AC contactor failure, let's first understand the role this component plays in the functioning of your air conditioner. An AC contactor serves as a switch that controls the flow of electricity to the compressor and condenser fan motor. When your thermostat detects the need for cooling, it sends a signal to the contactor, which, in turn, closes the circuit and allows electricity to flow to the compressor and fan motor. This initiates the cooling process. Once the desired temperature is reached, the thermostat sends a signal to the contactor to open the circuit, discontinuing the power supply and shutting off the air conditioner.

Symptoms of a Bad AC Contactor

Identifying a faulty AC contactor can be crucial in avoiding system breakdowns and expensive repairs. Here are some common symptoms that indicate a bad AC contactor:

1. Air Conditioner Not Cooling

If your air conditioner is running but fails to produce cool air, it may be an indication of a faulty contactor. A malfunctioning contactor can prevent the compressor from receiving power, resulting in inadequate cooling or no cooling at all.

2. Constant Tripping of Circuit Breaker

A failing AC contactor can draw more electrical current than it should, causing the circuit breaker to trip frequently. This occurs when the contactor fails to open the circuit when the cooling cycle is completed, leading to an overload of electrical current.

3. Buzzing or Humming Sounds

When an AC contactor is on the verge of failure, it may produce buzzing or humming sounds. These sounds can be a clear indication that the contactor is not functioning properly and may need to be replaced.

4. AC Unit Doesn't Turn On

In some cases, a bad contactor might prevent the air conditioning unit from turning on altogether. This issue is often accompanied by a lack of response from the system when the thermostat is adjusted, indicating an electrical problem.

5. Stuck Contact Points

Over time, the contact points within an AC contactor can become pitted and pockmarked, leading to insufficient contact between them. When this occurs, the contactor may not be able to transmit the necessary electrical current, resulting in a malfunctioning air conditioning unit.

Causes of AC Contactor Failure

Understanding what causes an AC contactor to fail can help you address potential issues promptly and prevent sudden system breakdowns. Here are some of the common causes of AC contactor failure:

1. Age and Wear

Like any mechanical or electrical component, AC contactors undergo wear and tear over time. As the contactor ages, the contact points can become worn, leading to arcing or pitting. Prolonged usage and regular cycling can accelerate the aging process, causing the contactor to fail prematurely.

2. Electrical Surges

Sudden power surges, often caused by lightning strikes or utility company fluctuations, can be detrimental to your AC contactor. The high voltage associated with electrical surges can overload the contactor, causing it to burn out or become damaged.

3. Contactor Size Mismatch

When replacing an AC contactor, it is crucial to ensure that the new component matches the specifications of the old one. Using an undersized contactor can lead to excessive wear and overheating, ultimately resulting in premature failure. On the other hand, an oversized contactor may not fit properly and can cause electrical arcing.

4. Pest Infestation

Believe it or not, pests such as ants and rodents can find their way into your electrical panel and wreak havoc on your AC contactor. These critters may chew on wires or build nests within the contactor, disrupting the electrical connections and causing failure.

5. Lack of Maintenance

Regular maintenance of your air conditioning system is important to keep all components in optimal condition. Failure to clean and inspect the contactor can lead to the accumulation of dirt, dust, and debris, hindering its functionality and potentially causing failure.

Preventing AC Contactor Failure

Now that we have identified the common causes of AC contactor failure, let's explore preventive measures you can take to avoid encountering such issues:

1. Schedule Regular HVAC Maintenance

Regular maintenance by a professional HVAC technician is essential to ensure the longevity and optimal performance of your air conditioning system. During routine maintenance visits, the contactor can be inspected, cleaned, and tested to detect any signs of wear or damage.

2. Keep the AC Condenser Clean

The condenser unit of your air conditioner is located outdoors and can accumulate dirt, leaves, and other debris. Keeping the condenser clean and free from obstructions ensures that the contactor and other components are not compromised by debris, optimizing their lifespan.

3. Install Surge Protectors

Protecting your air conditioning system from electrical surges is crucial. Installing surge protectors can help prevent damage to sensitive components like the contactor, extending its lifespan and preventing unexpected breakdowns.

4. Seal Potential Points of Entry

To prevent pests from entering your electrical panel and damaging the contactor, seal any potential points of entry. Use caulk or weatherstripping to seal gaps or holes that may allow pests to make their way inside.

5. Replace Worn Contactors

Regularly inspect the condition of your AC contactor and look for signs of wear, such as pitting or arcing. If you notice any damage, it is advisable to replace the contactor promptly to avoid system failure.


To keep your air conditioning system in prime condition, it is important to understand the causes of AC contactor failure and take appropriate preventive measures. From age and wear to pests and electrical surges, several factors can contribute to contactor failure. By scheduling regular HVAC maintenance, keeping the AC condenser clean, installing surge protectors, sealing potential points of entry, and replacing worn contactors, you can mitigate the risk of AC contactor failure and ensure the smooth operation of your air conditioning system for years to come. Remember, early detection and timely action can save you from costly repairs and uncomfortable situations, especially during scorching summer days.


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