How to Test an AC Relay

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  • 0.5-1
  • Intermediate
What You'll Need
Automotive test light

Testing an AC relay is more about a process of elimination than testing the relay itself. By testing the wires that go into the relay, you can diagnose if it is the relay itself, or something else that is causing the problem. Since every vehicle differs, your vehicle may not have some of the same wires and components. The tips included in this guide should help you with a guideline of what to test in your own vehicle.

Step 1 - Prep

Your first step is to turn your car on and turn your A/C on full blast. Open your hood, locate the a/c relay and remove it. Now with the a/c relay removed you are going to use an automotive test light to make sure that there is power going to the relay. You may want to make sure that your test light is working properly first, just test it on the car's battery. Make sure one end of your test light is grounded on any piece of metal that is attached to the chassis.

Step 2 - Test

Inside the block where the relay was located, there should be wires that supply the power to the relay. Insert the pointed end of the test light into each wire to test them. The test light will illuminate if there is power. If there is power going to the power wire, and the trigger wire then your relay is the issue.