how to check ac contactor


How to Check AC Contactor

One of the essential components in an air conditioning system is the AC contactor. The contactor is responsible for controlling the flow of electrical current to the compressor and the condenser fan motor. Over time, contactors can wear out or malfunction, leading to issues with your AC unit. To prevent any inconvenience, it is crucial to check your AC contactor regularly. In this article, we will guide you through the process of checking your AC contactor and ensuring its proper functionality.

Why is Checking the AC Contactor Important?

Before we dive into the steps of checking the AC contactor, let's first understand why it is essential to include this task in your regular maintenance routine. The contactor acts as a switch that allows electricity to flow to various components of the air conditioning system. Over time, the contactor can become pitted, burnt, or stuck, resulting in a poor connection or a complete failure. A malfunctioning contactor can lead to issues such as intermittent cooling, no cooling at all, or even damage to other electrical components of the AC system. By regularly checking the contactor, you can identify any potential problems early on and prevent major malfunctions or costly repairs.

Signs of a Faulty AC Contactor

Before you proceed with checking the AC contactor, it's essential to be aware of some signs that indicate a faulty contactor. Identifying these signs early can help you determine whether a more thorough inspection is necessary. Here are a few common indications of a faulty AC contactor:

1. Intermittent Cooling

If you notice that your AC unit is not consistently cooling your space, the contactor could be the culprit. A faulty contactor may lead to erratic power supply to the compressor, resulting in irregular cooling performance.

2. No Cooling at All

If the air conditioning system fails to produce any cool air, it could be due to a faulty contactor. A complete failure of the contactor would interrupt the power supply to crucial components needed for cooling.

3. Clicking Sounds

When the contactor is functioning correctly, you may hear a faint clicking sound as it engages and disengages. However, if you detect a continuous clicking noise, it could indicate that the contactor is stuck or not functioning correctly.

4. Burnt or Pitted Contacts

You can visually inspect the contactor for signs of wear and tear. Burnt or pitted contacts appear black or charred. If you notice any discoloration or damage on the contactor contacts, it is a strong indication that the contactor needs to be replaced.

5. Electrical Smells or Overheating

If you detect any unusual electrical smells or excessive heat emitting from the contactor, it is crucial to address the situation promptly. Overheating can be a sign of a malfunctioning contactor and should be inspected by a professional technician.

Now that we have familiarized ourselves with the importance of checking the AC contactor and the signs of a faulty contactor, let's move on to the steps on how to check your AC contactor.

Step 1: Safety First

Before starting any inspection or maintenance tasks, it is crucial to prioritize safety. Ensure that the power supply to the air conditioning system is completely turned off. You can do this by switching off the electrical circuit that powers the AC unit. It is also recommended to use an electrical tester to verify that there is no current flowing through the system. Safety should always be the top priority when working with electrical components.

Step 2: Accessing the AC Contactor

To begin the inspection, you will need to access the AC contactor. Start by locating the air conditioning unit's electrical panel. This panel is typically found near the condenser unit, either on an exterior wall or in a nearby mechanical room. Open the panel using the appropriate tools and remove any covers or protective housing to expose the contactor.

Step 3: Visual Inspection

With the contactor exposed, perform a visual inspection to check for any obvious signs of damage or wear. Look for burnt or pitted contacts, excessive dust or debris, loose wiring, or any physical damage to the contactor. Identifying visible issues can help determine whether a more in-depth inspection or replacement is necessary.

Step 4: Testing with a Multimeter

If the visual inspection does not reveal any obvious issues, it is time to proceed with testing the contactor using a multimeter. A multimeter is a versatile tool that can measure voltage, current, and resistance. Set the multimeter to the appropriate voltage measurement setting, usually AC voltage. Carefully touch the multimeter probes to the contactor's input and output terminals, ensuring that the probes make a secure connection. Check the voltage reading displayed on the multimeter. Consult the manufacturer's specifications to determine the acceptable voltage range for your contactor. If the reading falls outside the specified range, it is an indication of a faulty contactor that needs replacement.

Step 5: Checking the Coil

The AC contactor contains a coil that is responsible for engaging and disengaging the switch. If the previous steps did not reveal any issues, it's important to check the coil's functionality. Disconnect the power supply to the air conditioning unit and use the multimeter to measure the resistance of the coil. Refer to the manufacturer's specifications for the acceptable resistance range. A significant deviation from the specified range may indicate a faulty coil that needs to be replaced.

Step 6: Reassembling and Follow-up

If you have detected any issues with the AC contactor during the inspection and testing, it is advisable to replace the faulty component. Ensure that the replacement contactor is compatible with your air conditioning system and follow the manufacturer's instructions for installation. After reassembling the unit, restore the power supply and test the AC system to ensure that it is functioning correctly.


Regularly checking your AC contactor is a crucial maintenance task that helps ensure the proper functioning of your air conditioning system. By identifying and addressing any issues with the contactor promptly, you can avoid unexpected breakdowns and costly repairs. Remember to prioritize safety throughout the process and consult a professional technician if you are unsure or uncomfortable performing the inspection yourself. Taking the time to check your AC contactor can prolong the lifespan of your unit and keep you cool and comfortable during the hot summer months.


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