how to test ac contactor with multimeter


How to Test AC Contactor with Multimeter


When it comes to troubleshooting electrical issues in an AC unit, the contactor is often a culprit. The contactor is responsible for controlling the flow of electricity to the compressor and condenser fan motor in your air conditioning system. If the contactor is faulty or malfunctioning, it can result in various problems, including no cooling, frequent cycling, or even complete system failure.

Testing the AC contactor with a multimeter is a simple and effective way to determine whether it is functioning properly or needs replacement. In this article, we will guide you through the process of testing the AC contactor using a multimeter, ensuring you can diagnose the issue accurately and save money on unnecessary repairs.

Testing the AC Contactor

What You Will Need:

Before getting started, gather the following tools and materials:

- Multimeter (digital or analog)

- Screwdriver

- Insulated gloves

- Safety goggles

1. Turning Off the Power Supply

The first step before conducting any electrical tests is to ensure your safety. It is crucial to switch off the power supply to the AC unit before proceeding with any further steps. Locate the disconnect switch, typically located near the outdoor unit or on the main electrical panel, and turn it off. For additional safety, it is recommended to use insulated gloves and safety goggles throughout the process.

2. Accessing the Contactor

Once the power supply is turned off, locate the contactor. It is usually located inside the electrical control box, which can be accessed by removing the control panel cover. In some units, the contactor may be directly visible without the need for removing any covers. The contactor is identifiable by its rectangular shape with multiple terminals and a spring-loaded bar across it.

3. Inspecting for Physical Damage

Before proceeding with the electrical tests, visually inspect the contactor for any signs of physical damage or burnt-out components. Look for melted insulation, corroded terminals, or loose connections. If you notice any noticeable damage, it is recommended to replace the contactor rather than testing it, as physical damage indicates internal issues that cannot be resolved through testing alone.

4. Testing for Continuity

Continuity testing is an effective method to determine if the contactor's electromagnet or coil is functional. Set your multimeter to the continuity mode. Identify the terminals associated with the contactor's coil. Usually, these terminals are labeled "A1" and "A2" or "1" and "2". After selecting the appropriate terminals, touch the multimeter leads to each terminal. If you hear a beep or see a "0" resistance reading on the multimeter, it indicates that the coil has continuity and is functioning correctly. If there is no continuity, the coil may be faulty, and the contactor needs replacement.

5. Testing for Voltage

Testing for voltage is crucial to determine if the contactor is effectively controlling the electrical flow to the compressor and fan motor. To perform the voltage test, set your multimeter to the AC voltage mode. Locate the line terminals on the contactor, often labeled as "L1" and "L2" or "T1" and "T2". With the power supply turned on, carefully touch the multimeter leads to these terminals. You should ideally get a reading close to the rated voltage of your AC unit. If the voltage is significantly lower or zero, it indicates a faulty contactor that is not allowing electricity to pass through.


In conclusion, testing the AC contactor with a multimeter is a relatively simple process that can help diagnose and resolve electrical issues with your air conditioning system. By following the step-by-step guide provided above, you can determine whether the contactor is functioning correctly or needs replacement. Remember to prioritize safety by switching off the power supply and using insulated gloves and safety goggles.

Regularly testing the contactor in your AC unit can potentially save you from the inconvenience of system breakdowns and expensive repairs. If you suspect any issues with the contactor, such as frequent cycling or inadequate cooling, it is recommended to perform these tests and consult a professional if necessary. With proper knowledge and testing, you can keep your AC system in optimal condition and enjoy efficient cooling during hot summer months.


Just tell us your requirements, we can do more than you can imagine.
Send your inquiry

Send your inquiry

Choose a different language
Current language:English