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How To Test The Compressor In Your Central Air Conditioning Unit

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Your central air conditioning unit runs on a type of chemical fuel called refrigerant. The refrigerant starts out as a gas that the compressor pushes out into the condensing coils, which change the gas to liquid so the fuel can travel into your home and the air handler, where the actual air cooling happens. A problem with the compressor can keep the refrigerant gas from pumping out enough, or at all, and can leave you with a nonfunctional unit.

If you have some electrical experience and own a multi-meter, you can test your compressor to see if you will need a replacement. Leave the actual replacement to a certified air conditioner repairs technician since you don't want to play around with the chemical refrigerant.

What You Need:

  • Screwdriver
  • Owner's manual 
  • Multi-meter with continuity setting

Step 1: Locate the Compressor

Turn off the power to the condensing unit by pulling the fuse from the fuse box near the unit or by switching off the main breaker.

Remove the condensing unit cover by locating and removing its fasteners. The fasteners could be either screws, twist knobs, or levers, depending on the model of your unit. Set the condensing unit cover somewhere safely aside.

Locate the compressor using your owner's manual for a visual guide, if needed. Locate the terminal cover on the compressor and remove the screws holding the cover onto the main body. Pull off the cover and set the cover safely aside and place the screws in your pocket.

Step 2: Test the Compressor Terminals

Look at the now exposed terminals on the compressor. There are three terminals labeled "C", "R", and "S", respectively. You will want to test the continuity between each pair of these terminals.

Turn your multi-meter to the continuity setting. Place one multi-meter probe on the "C" terminal and the other on the "R" terminal. The multi-meter should beep if it senses continuity. Now remove the second probe and place it on the "S" while keeping the first probe on the "C". Listen for the beep or wait a moment without a beep then continue testing. Keep the second probe on the third terminal but move the first probe to the "R" terminal and take your final reading.

If any of the readings fail to make the multi-meter beep, your compressor has lost continuity and will need to be replaced. You will need to contact an HVAC company for a new compressor.

Step 3: Reassemble the Unit

If you don't plan on using the air conditioner until you have a service call, you can leave the compressor unhooked and simply put the condenser cover back on and fasten it into place. Leave the power fuse out of the box so that no one accidentally triggers the air conditioner into action.

Did the compressor test out normally and you want to put the unit back together for the service call to see what the problem actually is? Screw the terminal cover back on the compressor then attach the condensing unit cover. You can leave the fuse out of the air conditioner until the tech arrives. Consider contacting companies like A Absolute Plumbing & Heating for assistance.