View Full Version : Grounded compressor
01-22-2010, 08:36 PM
First post here. 6 year installer 1 year tech currently enrolled in a 2 year HVAC program at a West GA Tech. NATE certified ID # 1997427.
I had a no-heat call the other day on a Lennox HP. The breaker would trip just about as soon as the unit would try to run. Compressor LRA is 85 and read 83amps at startup until of course the breaker tripped. Recip compressor btw and capacitor was in good shape showing proper MFD. Next thought was to check the windings on the compressor. What got me was that each had a reading to ground. Run, start, and common. Diagnosed as grounded compressor heh. But is this common as everyone I seem to have asked has never seen it but it seems totally possible.
01-22-2010, 09:01 PM
No one you work with has ever seen a grounded compressor? Yeah, right. See them all the time.
01-22-2010, 09:11 PM
Well what i meant was its common to see one winding grounded. What was strange was that all three of them showed a reading to ground.
Sounds like you answered it.........
01-22-2010, 11:31 PM
01-22-2010, 11:49 PM
This thread belongs in the Professional technical forum.
01-23-2010, 12:26 AM
It can happen.
Its not actually 3 windings in a single phase compressor.
01-23-2010, 12:46 AM
Thats what I wanted him to question and then understand. There is only 2 windings in a single phase compressor. You have to picture that there are two motors in that shell and they are tied together at L1. So its very common to find them grounded at all terminals. Very Common. You will see plenty.
Shorted compressors are sometimes hard to diagnose with your meter. They throw the breaker as soon as its reset. The best way I have found to be certain its nothing else is disconnect common from the comp terminal without touching anything else. If it resets than it the comp for sure.
01-23-2010, 12:58 AM
I think a lot of people get screwed up because a 3 phase has 3 terminals. And they just associate 3 windings with 3 terminal post.
01-23-2010, 01:06 AM
Absolutely. Just remember if has a run cap its not three phase. And dont get confused and mistake a fan mtr run cap for the comp.
01-23-2010, 10:54 AM
...and remember to
I just caught myself posting something that could be DIY.
Get your count up and apply for pro membership.
See you in the Technical forum.
01-23-2010, 12:39 PM
Moved to Pro
01-23-2010, 12:43 PM
Ok, I moved this to pro and cleaned it up, moved back to residential.
To the original poster, threads like this are better off in the Professional Forums, get your 15 posts and apply for pro membership.
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