how to tell if the ac contactor is bad


How to Tell if the AC Contactor is Bad

Is your air conditioning system acting up, making strange noises, or failing to turn on? While there could be several possible causes, one component that often goes unnoticed is the AC contactor. The AC contactor is responsible for energizing the compressor and the condenser fan motor in your air conditioning unit. Over time, this crucial part may become worn out or develop faults, leading to various issues. In this article, we will guide you through the process of identifying whether your AC contactor is bad and needs replacement. By learning the signs to watch out for and understanding how to troubleshoot, you can prevent potential AC failures and ensure optimal cooling during those hot summer days.

Signs That Your AC Contactor Might be Bad

Recognizing the warning signs of a faulty AC contactor is essential in diagnosing the problem and taking the appropriate steps for repair. Here are some common indications that your AC contactor may be nearing the end of its lifespan:

1. Intermittent or Complete AC Unit Failure

If your air conditioning system frequently experiences intermittent or complete failure, it could be due to a bad AC contactor. When the contactor becomes faulty, it fails to send the electrical current required to start the compressor and condenser fan motor. This can result in reduced cooling capacity or the complete shutdown of your AC unit. If your system is experiencing recurring cooling failures, it's worth inspecting the contactor.

2. Unusual Clicking Sounds

Another sign of a malfunctioning AC contactor is the presence of unusual clicking or chattering sounds. The contactor consists of an electromechanical switch that controls the flow of electrical current to the compressor and condenser fan motor. When the contacts inside the contactor start to wear out or become pitted, they may produce an audible clicking noise. If you notice such sounds coming from your air conditioning unit, it's a clear indication that the contactor needs attention.

3. AC Unit Does Not Turn On

A failing AC contactor can prevent your air conditioning unit from turning on altogether. When you adjust the thermostat to cool your home but the AC unit remains unresponsive, it could be due to a faulty contactor. The contactor is responsible for connecting the power supply to the compressor and condenser fan motor, allowing them to start up. If the contactor fails to energize, no power will be dispatched to the essential components, resulting in a non-functioning AC system.

4. Worn or Burned Contact Points

Visually inspecting the contactor can provide valuable insights into its condition. The contactor consists of two contact points that are typically made of metal. Over time, these points may become worn out, pitted, or even burned due to excessive arcing. A visual examination of the contactor can reveal signs of wear and tear, such as discoloration, melting, or corrosion. If you notice any of these issues, it's likely that the contactor is failing and needs to be replaced.

5. Excessive Heat Build-up

When a contactor starts to fail, it often generates excessive heat. This can lead to noticeable heat build-up around the contactor area within the AC unit. If you feel intense heat emanating from the contactor or observe signs of melting insulation nearby, it's a clear indication of a faulty component. High levels of heat can cause further damage if not addressed promptly, potentially leading to more extensive repairs.

How to Troubleshoot a Bad AC Contactor

Now that you are familiar with the common signs of a failing AC contactor, it's time to learn how to troubleshoot the issue. Follow these steps to determine whether your contactor is the root cause of your air conditioning troubles:

1. Power Off the AC Unit

Before conducting any troubleshooting, ensure your safety by cutting off power to the AC unit. Locate the electrical breaker panel and switch off the circuit breaker that supplies electricity to the air conditioning system. This precautionary measure will prevent any accidental electrical shocks while handling the contactor.

2. Remove the Access Panel

To gain access to the contactor, remove the access panel situated on the exterior of the AC unit. The access panel is typically secured with screws or snaps, and can usually be removed with a screwdriver or by hand. Place the screws in a safe location to prevent loss.

3. Inspect the Contactor for Visible Damage

Once the access panel is removed, inspect the contactor for any signs of visible damage. Look for worn or burned contact points, melted insulation, or any loose or frayed wires. If you notice any obvious signs of wear and tear, it's highly likely that the contactor needs to be replaced.

4. Check for Continuity

To further diagnose the contactor, use a multimeter to check for continuity. Set the multimeter to the ohms or continuity setting and touch the probes to the contactor's input and output terminals. If the multimeter displays a reading of zero ohms or beeps, it indicates that the contactor is functioning correctly. However, if the meter shows no reading or fluctuating values, it suggests a fault in the contactor.

5. Test the Coil

The contactor coil is responsible for creating the magnetic field necessary to pull in the contactor's contacts. To test the coil, set the multimeter to the ohms setting and measure the resistance across the coil terminals. Consult the manufacturer's specifications to determine the acceptable resistance range. If the coil's resistance falls outside the specified range, the contactor's coil is likely faulty and needs replacement.

Preventive Measures to Extend the Contactor's Lifespan

While contactors are susceptible to wear and tear over time, there are several preventive measures you can take to extend their lifespan and minimize potential breakdowns. By implementing the following practices, you can ensure the longevity of your AC contactor and optimize the performance of your air conditioning system:

1. Regular Maintenance

Including your AC contactor in routine maintenance procedures is vital to prevent potential problems. During annual HVAC tune-ups, have a professional inspect the contactor for any signs of wear, pitting, or burning. They can also clean the contact points and ensure the contactor is functioning optimally. Regular maintenance allows for early detection of issues and can save you from more significant repairs in the future.

2. Keep the Area Around the AC Unit Clear

To maintain proper airflow and prevent overheating, it's essential to clear any debris, vegetation, or obstructions around the AC unit. Leaves, branches, or other objects can accumulate around the contactor, impeding its heat dissipation and causing it to work harder. By keeping the area around the AC unit clear, you facilitate better cooling performance and reduce strain on the contactor.

3. Protect Against Power Surges

Power surges can damage electronic components, including the AC contactor, resulting in premature failure. To safeguard your air conditioning system against power surges, consider installing a whole-house surge protector. These devices absorb excessive voltage spikes, ensuring that your equipment remains protected from potential damage.

4. Maintain Proper Electrical Connections

Periodically inspect the electrical connections leading to the contactor and ensure they are secure and free from corrosion. Loose or damaged wires can prevent the contactor from receiving the necessary power supply, leading to performance issues. Tighten any loose connections and repair or replace any damaged wires to maintain optimal electrical flow.


The AC contactor plays a crucial role in the functioning of your air conditioning system. Being aware of the signs of a bad contactor can save you from uncomfortable temperatures and potential system failures. Remember to look out for intermittent or complete AC unit failure, unusual clicking sounds, failure to turn on, worn or burned contact points, and excessive heat build-up. Troubleshooting a failing contactor involves visually inspecting the component, checking for continuity and coil resistance, all while ensuring safe handling practices. By taking preventive measures and including the contactor in regular maintenance routines, you can extend its lifespan and keep your air conditioning system running smoothly for years to come.


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