AC Condensor and Fan Not Running

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Old 09-12-09, 12:27 PM
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AC Compressor and Fan Not Running

This morning, I noticed my AC wasnt cooling. The blower motor on the air handler is working and pushing air thru, but the unit outside isnt working. Whenever the thermostat is set to cool, the circuit breaker pops. I went outside and removed the cover and checked the voltage coming in, which was 24 volts. But because the breaker keeps tripping, I am unable to check the voltage out. Would this be an indication of a bad contactor? Thanks for the help.

Steve
 

Last edited by keetrock; 09-12-09 at 02:52 PM.
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  #2  
Old 09-12-09, 03:50 PM
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Just tested the compressor to see if it was grounding out, not sure if i was doing it right. I had the power OFF to the unit, and I put the one lead of the multimeter on the compressor lead and the other lead was touching a clean spot on the tube going into the compressor. I was getting no reading. Did I need to have power applied to get an accurate reading?
 
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Old 09-13-09, 09:03 PM
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Originally Posted by keetrock View Post
Just tested the compressor to see if it was grounding out, not sure if i was doing it right. I had the power OFF to the unit, and I put the one lead of the multimeter on the compressor lead and the other lead was touching a clean spot on the tube going into the compressor. I was getting no reading. Did I need to have power applied to get an accurate reading?
This is pushing the limits of DIY but you need to have all of the wires off of the compressor to check if your compressor windings are shorted to ground. POWER OFF! You must use the ohm setting on your meeter to do this. I highly suggest that you have a professional look at your system as it's now unavoidable anyway.
 
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Old 09-16-09, 06:40 PM
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Make sure NO power is applied when you are making these test.
Cut the circuit breakers. Remove the disconnects. Make sure power is OFF!!!.

Don't worry about the 24 VAC control voltage. That is coming from the air handler or a 24 volt transformer in the condensing unit itself.

Set your ohmmeter to a low ohms scale such as 10 ohms.

There should be a 3 wire plug on the side of your compressor.

Place one probe an any of the terminals.
Measure the resistance to the other two terminals.
You should get a reading of 2~3~4 ohms.

There should be a low resistance connection between all three of the teminals. These are the motor windings. The start winding and the run windings. They are fairly large, heavy wire so they resistance values will be small.

Keeping one meter lead on one of the compressor wires, place the opposite wire on the case of the unit or a clean place on the compressor.
There should be NO connection between the compressor windings and ground.
If there is such a connection, the compressor is bad.
That's not the only way the motor in the compressor can fail electrically.
If one or more of the windings inside the compressor has shorted then it will also overload the breaker.

In your case, here's what 'could' be tripping the breaker:
1) Wiring chaffed to ground or insulation failure
2) The compressor can be at fault
3) The condensor fan can be causing the problem
4) The start/run capacitor may have become internally shorted to ground.

Remember you are working with 220/240 VAC voltages that ARE lethal. Not 'may' be. A-R-E.
If you aren't experienced with working on this kind of thing, call your AC man.
If you don't know if power should be on or off when checking ohms..... you probably should call the man.
220 is VERY unforgiving, it's NOT like 120 vac at all when it get's ahold of you. When it does you won't be able to shake it off. VERY dangerous.
 
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Old 09-21-09, 09:42 AM
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Compressor was grounded out. Thank god it's the end of the summer! Thanks for all the help guys.
 
  #6  
Old 09-21-09, 01:43 PM
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Glad you found it. Shorted compressor is always BAD news however.
 
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