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Old 03-03-2012, 11:02 AM   #1
snorky18
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Default I think my heat pump's compressor is toast

It's the Rheem 2 Ton Split Unit for our upstairs. It was installed in 2005 when the house was built.

The fan works fine, but I noticed it was "too quiet" outside (the fan was the only noise from the condenser), then once every 30 seconds was a loud electrical buzz/hum for about 1 second. So I broke out the multimeter.

The dual run capacitor checked out fine. There did not seem to be a start capacitor (I sort of thought there should be, but the factory wiring diagram says it is optional for this unit).

The loud hum was indeed the compressor trying to come on, and pulling 80 amps for that ~ one second of humming.

I haven't had a chance to check the resistance across the compressor's windings yet.

What else I should check before accepting that I need a new compressor?

(BTW-Yes, I know I that can't discharge/evacuate the unit or refill it without upsetting the EPA, and no, I'm not going to do that).
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Old 03-03-2012, 02:14 PM   #2
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Default Re: I think my heat pump's compressor is toast

I'd invest in the start capacitor before spending the big bucks. Make sure you have 220v at the motor, both legs pulling 80 amps. Otherwise sounds spendy :-(
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Old 03-03-2012, 03:48 PM   #3
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Default Re: I think my heat pump's compressor is toast

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I'd invest in the start capacitor before spending the big bucks.
I know the start capacitor makes it easier for the compressor to start, and also should make it last longer, but can it actually rescue a locked compressor? To me if it's pulling 80 Amps on both motor wires for almost a full second and not budging at all, I question if the extra oomph from the start capacitor would really make a difference.


Quote:
Originally Posted by pop pop View Post
Make sure you have 220v at the motor, both legs pulling 80 amps.
Done and done.

Quote:
Originally Posted by pop pop View Post
Otherwise sounds spendy :-(
Yup

Then I have thoughts like, "Well, this one is 7 years old, and probably slightly undersized, and a whole new 15 Seer 2.5 Ton is only ~$2K, if I run the lines myself, set the condenser and handler myself, then pay a tech a few hundred $ to make the connections, draw vaccum, and charge the system, so maybe $2500 total". - See, a compressor is is expensive, but then I start have those thoughts, then it costs even more.
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Old 03-04-2012, 12:09 PM   #4
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Default Re: I think my heat pump's compressor is toast

The compresor may be locked up, or shorted to ground, but here is how I test one to leave no doubt. Make sure you shut off the circuit breaker, and pull the fuses on the service dissconect box next to the unit. Remove the panel to gain access to the compressor. Short the run capacitors out, as they are probably charged up. On the compressor, there are 3 terminals, Start, Run, and Common. Set your meter to resistance, and check each terminal to ground, to see if the compressor is shorted. If it is not, check each terminal to each other, to see if you have a resistance reading (you can find the specific value in ohms if you look it up), if you have readings, put your wires back on the correct terminals and re-install the cover. What you have is called a permanete split capacitor system, that has no start capacitor, correct? Check each capacitor for open, or shorted to ground, and mfd reading, if you can. If all this checks out, the compressor is probably stuck, and you can try and pound on the top of it with a plastic dead blow hammer, and or wire a start capcitor in it, to try and break it free. If it still does not free up, your last option is to kick the compressor motor in reverse. This can be done by changing the wiring, or if you have a "Annie" type compressor annalyzer. If you do get it to free up, consider installing a hard start kit on it, which has a start capacitor and relay in it. 7 years is way too early for the compresoor to die, unless you got a bad one, or it is infact burned out. If it does come down to getting a new one, you should consider just getting a complete condensing unit wholesale, verses the compressor. IMO

Edit: I added a picture of my Annie Compressor Analyzer, that works great, if you can borrow one. For about 25 years before I purchased this, I just wired a 500 mfd start capacitor in, the old fashion way, to kick a compresor backwards.

Good Luck,

Wayne
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Last edited by lzenglish; 03-04-2012 at 12:38 PM. Reason: added pictues
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Old 03-04-2012, 12:33 PM   #5
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Default Re: I think my heat pump's compressor is toast

What Wayne said!
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Old 03-10-2012, 11:44 AM   #6
snorky18
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Default Re: I think my heat pump's compressor is toast

LZEnglish / Wayne, Thanks so much for your answer!

I went through everything you said, the compressor was fine electrically, and I ordered a hard start kit.

After installing the kit, the good news is the compressor started, the bad news is that it sounded like it had gravel for bearings. At any rate, I'm glad I did everything possible to determine the problem and see if I could fix it before calling in the high dollar assistance.

I guess the other "good" news is that I am probably going to get a larger and more efficient system as well (old one was 10 SEER). The system that we have is a bit undersized, and has never been able to keep up in the summertime. It only cooled to 86 upstairs in the summer in the afternoons, and this is the first summer we will have a baby up there, so we were going to have to do something anyway.

I'm going to make sure the ductwork sizing is adequate, then probably go up to 2.5 ton from the current 2 ton, as well as adding variable speed, and higher efficiency.

I'm also considering going geothermal (which would be at least partially DIY-at a minimum I would do the excavation for the horizontal loops). I'm open to suggestions/warnings/advice on it as well.

It's fairly temperate weather here right now, so I have a few weeks to figure it out before it gets really hot upstairs.

Thanks again Wayne!
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Old 03-10-2012, 01:27 PM   #7
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Default Re: I think my heat pump's compressor is toast

Quote:
Originally Posted by snorky18 View Post
I know the start capacitor makes it easier for the compressor to start, and also should make it last longer, but can it actually rescue a locked compressor? To me if it's pulling 80 Amps on both motor wires for almost a full second and not budging at all, I question if the extra oomph from the start capacitor would really make a difference.
...
The start capacitor doesn't provide "extra oomph", the start capacitor changes the phase angle to create a rotating magnetic field to start the motor. If the power in both windings is static, the motor won't start, no matter how much current is drawn. Now, the start capacitor also provides power limiting, but that's not the main issue here. Understanding how split phase, capacitor start, motors work is what's important.
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Old 03-10-2012, 06:56 PM   #8
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Default Re: I think my heat pump's compressor is toast

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LZEnglish / Wayne, Thanks so much for your answer!

You are Very Welcome snorky! I was sorry to hear about your compressor being mechanicaly wasted inside.

Take care, and Thanks for taking the time to say Thank You!

Wayne
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