How to Troubleshoot a Window AC Compressor

Tom Fritchman

When your window-mounted air conditioner starts to malfunction, you may not want to immediately replace the entire unit. It is very likely that you can repair or replace just one part of your air conditioner. This will extend the life of your purchase.

A malfunctioning window-mounted air conditioner might spew warm air into a room or it might not turn on at all.

If your window air conditioner ceases to cool your air, chances are its compressor is malfunctioning.

  1. Verify your power outlet works by unplugging the air conditioner and replacing it with a lamp. If the lamp turns on, then the problem is inside your air conditioner.

  2. Remove the terminal cover by unscrewing the four mounting screws with your screwdriver. These four screws are located near the four corners of your air conditioner’s front.

  3. Inspect your air conditioner’s compressor. If you see any cracked valves inside the air conditioner, then the entire compressor will need to be replaced. If the valves appear undamaged, then the problem is not the compressor. Instead, the problem lies in your air conditioner's electrical terminals.

  4. Locate the terminals labeled "C," "R" and "S." Inspect the wires connecting each terminal to the other two. If any of the wires appear damaged, they will need to be removed and replaced with your spare wire.

  5. Check the resistance between terminal "C" and terminal "R" by removing the wire that connects those two terminals and replacing it with the ends of your multimeter. If the multimeter reading shows a result higher than 30 ohms, one of the panels is faulty.

  6. Determine which terminal is faulty by repeating the resistance test for the connection between panel "C" and panel "S." Repeat the test again for the connection from terminal "R" to terminal "S." Use the process of elimination to determine which terminal will need to be replaced. If each of these tests shows resistance higher than 30 ohms, then the entire air conditioner will have to be replaced.


If your air conditioner is leaking refrigerant, check with your local authorities to verify local disposal laws.