How To Test And Replace An AC Contactor

Posted on: 3 May 2016

The contactor on a central air conditioner is an electrical part that receives the signal from your home's thermostat and then starts the unit into action. Problems with the contactor can cause rapid cycling – or turning on and then immediately off – or prevent the unit from turning on at all.

You can test the contactor yourself if you own a multi-meter with built-in continuity testing, and removing and replacing the part, if necessary, are fairly easy tasks.

Things You Need:

  • Socket wrench
  • Pliers
  • Multi-meter with continuity testing
  • New contactor, if needed

Step 1: Remove the Contactor

Turn off all electricity to the unit by pulling out the fuses in the fuse box near the unit or by switching off the power at the main circuit breaker.

Locate the access panel on the exterior wall of the condensing unit. Use a socket wrench to remove the fasteners holding the panel door in place. Place the panel door off to the side, on the ground, and sit the fasteners on the door for safekeeping.

You can now see the contactor, which is attached to the unit with wires. Note the orientation of the wires so that you can hook the wires up to the correct terminals when replacing the part. Use a pair of pliers to pull firmly on the end of each wire to pop the wire out of its terminal.

Use the socket wrench to remove the mounting screws for the contactor. Pull the contactor off its mounting plate and set the contactor on a table for testing.

Step 2: Test the Contactor

Test the contactor for continuity using a multi-meter set to the continuity setting. Attach the probes for the multi-meter to the terminals on the contactor. Listen for the multi-meter to beep, which indicates continuity and suggests that there might be another problem with your unit.

If the multi-meter doesn't beep, you can continue with the part replacement.

Step 3: Install the New Contactor

Line the new contactor up with the mounting screw holes on the mounting plate. Attach the mounting screws with the socket wrench. Hook the wires up to the appropriate terminals on the new contactor.

Realign the access panel door onto the condensing unit. Use the socket wrench to attach the fasteners to secure the door into place. Restore power at the fuse box or circuit breaker before conducting a test run. If any problems persist, contact an air conditioning repair service.


Lowering Your HVAC Expenses

After we purchased our very first home, I realized that I was really struggling with paying for the heating and cooling costs. We were spending much, much more money every month than we thought we were going to, and it was really difficult to figure out what we should do. We thought long and hard about how to minimize our expenses, but we didn't really get anywhere until we talked with an HVAC contractor. He mentioned specific, actionable ways to lower our bill, such as programming our thermostat and using more of our ceiling fans. This blog is all about lowering your bill.

Latest Posts