Burning Up Compressors?


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Old 06-29-10, 09:44 AM
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Burning Up Compressors?

Hello All,

I purchased my house new about 7 years ago. In our 4th summer there, the compressor (we have a split unit) stopped working (actually seemed like it was having a hard time starting just prior to it going out.). The fan still blew but it was just hot air. I had an AC guy come out and look. I walked with him during testing. We found that
1. the breaker was tripped (I already knew that but it kept tripping)
2. when we re-set it and turned the AC on, the breaker made a loud hum, the electric meter spun like crazy (he said he never saw one spin so fast) and the breaker would then trip.
3. The compressor was burnt up (according to him). We could see where the wiring harness connected to the compressor, it was basically charcoal and fell apart when you touched it.
He recommended purchasing a new compressor unit rather then repairing because of the cost of the repair and I would be getting a new unit with a better SEER rating. So we did and everything had been fine.

Now 3 summers later. Seemed like the AC was having a hard time starting again. We heard the compressor start then stop. Then start again and stay on. Did that for about three weeks (I should have called someone I know but I didn't have the $ for a tech this month) and stopped last night. I found almost the same thing as before. The breaker was tripped. When I reset it, and started the AC, I hear the loud hum at the circuit breaker and the electric meter spins. It stops for a few seconds and then does it again. This time it does not trip the breaker though but the AC doesn't start either. I turned off the AC because even though I know nothing about AC I know that it cant be good to let it continue to try to start.

So my question is what the heck is going on? How can I burn up two new compressors in 7 summers? Do I have an electrical problem that is doing this? I don't know if I should call an electrician or an AC guy. Really I don't know if the compressor is burnt up but it has the same symptoms. What else could it be?

Thank you for any help you can give!
 
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Old 06-29-10, 01:04 PM
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It could be a bad or weak start capacitor. If the compressor tries to start but doesn't after a couple of seconds (while drawing locked-rotor amps), the breaker will trip. Also, low voltage can cause failure to start.

Either a HVAC guy or a good electrician should be able to diagnose. Or, if you are a DIYer, you can try replacing the capacitor. They make hard-start capacitors that you could try.

I don't think your compressor is burned up.
 
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Old 06-29-10, 01:37 PM
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So is the capacitor part of the condenser/compressor unit or a separate piece? Why would that issue come back after replacing the condenser with a new one?

Just trying to understand. Not disagreeing with you.

Thanks!
 
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Old 06-29-10, 02:25 PM
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Originally Posted by djoaquin View Post
So is the capacitor part of the condenser/compressor unit or a separate piece?
Yes, the capacitor comes with the condenser unit - but it's a separate, relatively inexpensive component inside the cabinet. I don't know why it would fail after just three years. Maybe that's not the problem - it's just a theory. Low voltage can also cause failure to start.
 
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Old 06-29-10, 03:50 PM
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Could low voltage or repeated failure to start cause the wiring harness to burn to a crisp? I remember the AC guy who looked at the one we replaced a few years back saying something about it looked like it was starting and stopping over and over again which burnt it up. Or maybe it was trying to start over and over again?
 
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Old 06-29-10, 04:02 PM
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Originally Posted by djoaquin View Post
Could low voltage or repeated failure to start cause the wiring harness to burn to a crisp?
Not likely. That's what the circuit breaker, properly sized, should prevent.

What wiring harness? The 240V? I think the main 240-V wiring is usually not in a harness - it's individual conductors. The 24-V control wiring may be in a harness. I stand to be corrected.
 
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Old 06-29-10, 04:26 PM
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When we looked at the outside unit by taking the top off, I believe the compressor is what sits in the middle right? There were a few wires going into the compressor. At the point where the wires go in, there was a plug or maybe it was just a rubber gromit. That is the point where everything was charcoal. Seems to me he pulled the wires and a plug came out with some of the spades in it. Some of the spades stayed in the male side some pulled out because it was all crispy.

Does that make sense. That's were he said that the thing must have been overheating.
 
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Old 07-02-10, 09:00 AM
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Fixed

Just wanted to update everyone on the fix. It was the capacitor. It had gone bad. Once I replaced it, the compressor starts up with no trouble each and every time.

Thank you for your help Mike Speed 30!

Daniel
 
 

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