why contactor bad on ac


The Contactor Bad on AC: Causes, Symptoms, and Solutions


Air conditioning is one of the most essential appliances in our lives, especially during scorching summer days. It keeps us cool and comfortable in our homes, offices, and other indoor spaces. However, what happens when our trusty AC unit starts acting up and fails to function properly? One of the common culprits behind AC malfunctions is a faulty contactor. In this article, we will delve into the reasons why a contactor can go bad on an AC unit, the symptoms to look out for, and the necessary solutions to tackle this issue.

What is a Contactor and How Does it Work?

A contactor is an electrical switch that controls the flow of electricity to various components within an AC unit. It plays a crucial role in initiating and terminating the circuit between the power source and the compressor. The contactor consists of a coil, which when energized, creates a magnetic field that pulls down on the contacts, allowing electrical current to flow. When the coil de-energizes, the magnetic field weakens, and the contacts separate, cutting off the power supply. This cyclical operation of the contactor allows the AC unit to function as intended.

Causes of a Bad Contactor

There are several factors that can lead to a faulty contactor in an AC unit. Understanding these causes can help in diagnosing the problem accurately and taking appropriate measures to rectify it.

Aging and Wear

Over time, the internal components of a contactor can deteriorate due to general wear and tear. The constant opening and closing of the contacts, exposure to heat generated by the AC unit, and vibrations can all contribute to the aging process. Eventually, the contacts may become pitted, burnt, or worn out, resulting in a bad contactor.

Electrical Arcing

Electrical arcing refers to the phenomenon of sparks jumping between two electrical contacts. This can occur if the contacts are misaligned or contaminated with dirt, grime, or corrosion. When arcing happens, the contacts can become damaged or welding can occur, leading to a malfunctioning contactor.

Power Surges

Power surges can happen due to lightning strikes, utility grid fluctuations, or sudden voltage spikes. These surges can overload the electrical components of an AC unit, including the contactor. Continuous exposure to power surges can cause damage to the contactor's coil, contacts, or both.

Symptoms of a Bad Contactor

Identifying the symptoms of a bad contactor can help you detect the issue early and prevent further complications. Here are some common signs that indicate a faulty contactor:

AC Unit Not Turning On

If your AC unit fails to turn on despite electricity being supplied to it, a malfunctioning contactor could be to blame. When the contacts are worn out or burnt, they may fail to make a proper connection, resulting in no power reaching the unit.

Frequent Circuit Breaker Tripping

A contactor that is struggling to function correctly may cause excessive electrical current flow, leading to the tripping of the circuit breaker. This safety mechanism is designed to protect the AC unit from potential damage caused by electrical overload.

Strange Noises

A bad contactor can produce unusual sounds when it is beginning to fail. You might hear buzzing, humming, or clicking noises coming from the AC unit. These noises indicate that the contacts are not making a consistent connection, resulting in arcing or incomplete electrical flow.

AC Unit Cycling On and Off Rapidly

When a contactor is malfunctioning, it may cause the AC unit to cycle on and off rapidly or unexpectedly. This can be attributed to the contacts not closing properly, leading to an intermittent supply of power to the unit.

Burning Smell

If you notice a distinct burning smell coming from your AC unit, it could be due to a failing contactor. Overheating of the contacts, usually caused by arcing or excessive electrical resistance, can generate a burning odor that warrants immediate attention.

Solutions for a Bad Contactor

Once you have identified a faulty contactor as the cause of your AC troubles, it is essential to take appropriate action. Here are some solutions to consider:

1. Contact a Professional

If you are unsure about handling electrical components or lack the necessary expertise, it is always best to seek professional assistance. A certified HVAC technician can accurately diagnose the problem, replace the faulty contactor, and ensure the AC unit functions optimally.

2. Inspect and Clean the Contacts

In some cases, the issue with the contactor may be due to dirt, grime, or corrosion buildup on the contacts. Carefully inspect the contactor and, if needed, use a soft brush or a contact cleaning solution to clean the contacts. However, exercise caution and remember to turn off the power before attempting any maintenance.

3. Replace the Contactor

If the contactor is significantly damaged or worn out, it is advisable to replace it entirely. New contactors are readily available in the market and can be sourced from HVAC suppliers or authorized dealers. Ensure you purchase the correct model that is compatible with your AC unit.

4. Regular Maintenance

Prevention is better than cure, and regular maintenance can help prolong the lifespan of your AC components, including the contactor. Schedule routine check-ups with a professional technician who can inspect, clean, and lubricate the contactor to ensure it stays in good working condition.


A faulty contactor can disrupt the smooth operation of your AC unit and leave you feeling hot and frustrated, especially during scorching summer days. By understanding the causes, symptoms, and solutions related to a bad contactor, you can address the issue promptly and restore the comfort of your indoor environment. Remember to prioritize safety and seek professional help if you are uncertain about handling electrical components. By taking proactive measures, you can ensure your AC unit remains reliable and provides cool relief whenever you need it most.


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