How I Troubleshoot an Air Conditioner Compressor
Channel: Fox Family Heating and Air Conditioning
Date: 2021-04-10

If you are researching how to troubleshoot an air conditioner compressor, you've come to the right spot.  In this video I will describe step by step how I troubleshoot a compressor.

As someone who has been in the HVAC field since 2010, I can show you How I  troubleshoot an air conditioner compressor.  It's a step by step process that tales patience, but also takes  a good bit of knowledge.

First troubleshoot for a short to ground.  Before going anywhere, check at the contactor to see if anything is shorted to ground.  Put your meter setting on "continuity" check.  Put one meter lead on the left terminal on the load side of the contactor and one to ground.  Do you have continuity there?  Try the other load terminal to ground.  Do you have continuity there?  
If you have continuity at either of these terminals to ground, then something downstream is shorted to ground. Now you just have to troubleshoot it.  It could be:
1. Any of the high voltage wiring.
2. The contactor
3. The capacitor or start capacitor
4. The condenser fan motor
5. The crankcase heater
Measure the line voltage coming from the house
Ohm out the compressor at the air conditioner.
I usually just do this with the wires at the service panel still connected to the compressor.  If I see something screwy, I'll make an effort to check at the terminals themselves.
Internal Overload on the compressor can happen when it is running so hard the compressor heats up and shuts down to protect itself.
Ohm out the windings of the compressor.  Check your ohm's with your multimeter reading between Common and Start, Common and Run, and Start to Run.  Without going crazy in-depth on it in this video, generally, you'll notice the resistance between Common and Start will be a little higher than Common and Run.  The total of those two numbers is what you'll read between Start and Run.  So, if you had 2.3 ohms between Common and Start and 1.7 between Common and Run, you should have about 4 ohms between Start and Run.
Does it have a locked rotor or a stuck rotor? A stuck compressor can be fixed with a hard start kit.  It can give it a boost that is needed to get the compressor moving again.
So many things can happen to a compressor to cause it to fail.  Not only do you have to diagnose the bad compressor, but you also have to find out why it's not working.  

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0:00 Intro
0:45 Check for a short to ground
1:23 Ohm out the compressor
3:23 If the windings are good, check the breaker
5:04 Locked rotor / Hard start kit
5:43 Measure the line voltage to see if it dips
6:08 Bypassing the compressor to see if the fan is good
6:44 Internal overload on the compressor
8:19 Bad valves?  Are you sure?
9:17 Some other things to check