how to check an ac contactor



One of the essential components of an air conditioning system is the AC contactor. This device controls the flow of electricity to the compressor and the fan motor, ensuring that the cooling system works properly. However, over time, contactors can become worn or damaged, leading to malfunctions in the AC unit. It is crucial to regularly check the AC contactor to identify any issues and take necessary measures to prevent further damage and enhance the overall performance of the air conditioning system. In this article, we will provide a step-by-step guide on how to check an AC contactor, allowing you to maintain your AC unit effectively.

Why is Checking the AC Contactor Important?

The AC contactor plays a vital role in the operation of your air conditioning system. When you adjust the thermostat to lower the temperature, the contactor receives a signal to activate the compressor and the fan motor. This results in cool air being circulated throughout the room. Due to frequent usage and exposure to electrical currents, the contacts inside the contactor can get dirty, worn out, or corroded, creating resistance and hindering the electrical flow. Inadequate maintenance and failure to check the AC contactor can lead to issues such as reduced cooling efficiency, increased energy consumption, and even an AC system breakdown.

How to Safely Check an AC Contactor:

Before delving into the steps of checking the AC contactor, it is crucial to prioritize your safety. Remember to disconnect the power supply to the air conditioning unit by switching off the circuit breaker or unplugging the unit from the power source. This precautionary measure will minimize the risk of electrical shock while examining the contactor.

Gather the Necessary Tools:

To effectively check the AC contactor, you will need a few tools. These typically include a pair of insulated gloves, a voltage tester, and a screwdriver. The insulated gloves will provide protection against electric shock, and the voltage tester will ensure that there is no electrical charge present before commencing the inspection. Additionally, the screwdriver will be necessary to remove the cover of the contactor.

Inspect for Physical Damage:

The first step in checking the AC contactor is to visually inspect it for any signs of physical damage. Look for cracks, burn marks, or melted plastic components. If you notice any of these issues, it is crucial to replace the contactor immediately, as physical damage can hinder its proper functioning. Damaged contactors can lead to electrical arcs and short circuits, which pose a significant safety hazard.

Check for Loose Connections:

After examining the contactor for physical damage, the next step is to ensure that all connections are secure. Using a screwdriver, carefully remove the cover of the contactor. Check each terminal where the wires are connected to see if they are firmly attached. If you find any loose connections, tighten them using the screwdriver. Loose connections can lead to overheating, which can eventually cause damage to the contactor or other components of the air conditioning system.

Examine the Contacts:

The contacts are an integral part of the AC contactor, as they conduct the electrical current. Over time, the contacts can become dirty, corroded, or pitted, resulting in poor electrical flow. To examine the contacts, use insulated gloves and visually inspect each set. Look for signs of rust, pitting, or discoloration. If the contacts appear damaged, they will need to be replaced. However, if the contacts are only dirty or corroded, they can be cleaned using a soft cloth and contact cleaner. Gently rub the contacts until they are clean and free from any debris or corrosion.

Test for Electrical Charge:

Before proceeding further, it is essential to ensure that there is no electrical charge present in the contactor. This step is crucial to prevent electric shock while conducting the inspection. Using a voltage tester, follow the manufacturer's instructions to verify that there is no electrical current in the contactor. If the voltage tester indicates the presence of electricity, do not proceed with the inspection and contact a professional technician for assistance.

Measure the Continuity:

To determine the functionality of the contactor, it is necessary to measure the continuity. Continuity refers to the unbroken flow of electrical current through the contactor. Again, follow safety measures and disconnect the power supply to the air conditioning unit. Set the multimeter to the continuity function and touch the probes to each contact of the contactor. If the multimeter emits a continuous beep or shows a very low resistance reading, it indicates that the contactor has proper continuity. However, if there is no beep or a high resistance reading, it implies that the contactor is faulty and needs to be replaced.

Inspect the Coil:

The coil is another crucial component of the AC contactor. It is responsible for creating the electromagnetic field that activates the contacts when the thermostat signals the cooling system to turn on. Visually inspect the coil for any signs of damage, such as burns or cracks. If the coil appears to be damaged, it is imperative to replace the entire contactor, as attempting to repair the coil can be dangerous. Damaged coils can result in erratic contactor operation and system malfunction.


Regularly checking the AC contactor is crucial to ensure the optimal performance of your air conditioning system. By visually inspecting the physical condition, tightening loose connections, examining the contacts, testing for electrical charge, measuring continuity, and inspecting the coil, you can identify any issues with the contactor and take appropriate actions. If you notice any problems with the contactor that are beyond your expertise, it is advisable to seek professional assistance. Remember, thorough and routine checks will extend the lifespan of your AC unit and enhance its efficiency, ensuring cool and comfortable air during hot summer days.


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