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Old 06-07-2008, 02:29 PM   #1
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Bad compressor, and coil question...


Im currently trying to troubleshoot my HVAC (heat pump) which I suspect has a bad compressor. I've been able to test the compressor resistance across S-C-R. (S-R=1.88KΩ, S-C=2.3Ω, R-C= 1.88KΩ) which means the compressor is shorted, if I'm not mistaken.
The unit inside (furnace=York N2AHD10A06A) has a coil that does not look like it's the original heat exchanger. It looks like the original must have deteriorated and replaced by the one currently installed. It does not seem too deteriorated but its rather small IMO. Basically two aluminum radiator type panels in "V" shape close to each other with a drip pan under them, a bit corroded by the way. My question is, would it be possible that this coil is too small for the task and is overworking the compressor? (Compressor has only 4 years since installed, 5 years warranty non transferable ....
Thanks in advance for your help, its starting to get hot.

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Old 06-07-2008, 03:21 PM   #2
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Bad compressor, and coil question...


Here are some pictures...
Here's the indoors unit.


Notice the plumbing to the coil passes through a cutout/hand made plate and not the holes provided in the OE unit.


Same with the drain plumbing.


Heres the exposed coil. Notice the size and the plate to the right of the coil. It's there to support the coil and to eliminate air flowing past the coil.


Finally, an image of the fins. There is some deterioration throughout on both sides on the front face. In the interior sides there is not much deterioration.(air flow out)

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Old 06-07-2008, 03:44 PM   #3
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Bad compressor, and coil question...


This must be a downdraft unit, otherwise the coil is upside down. The plumbing and drain looks ok to me. If the compressor size does not match the size of the house, over or under, it reduces the life of the components.
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Old 06-07-2008, 06:57 PM   #4
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Bad compressor, and coil question...


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Originally Posted by muddog View Post
This must be a downdraft unit, otherwise the coil is upside down. The plumbing and drain looks ok to me. If the compressor size does not match the size of the house, over or under, it reduces the life of the components.
I believe the flow is upward. The filter is right below. The coil it basically two flat panels in a "V" with a drip pan at the lower portion. Are compressors rated to a coil size? How would I know that this coil is an appropriate size for the outdoor unit? How much does it typically cost to replace a compressor and what's involved? Thanks for your help.
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Old 06-07-2008, 07:12 PM   #5
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Bad compressor, and coil question...


your compressor and coil need to be rated to your furnace size. The furnace is rated by BTU the compressor are rated in tons, 1 ton 2 ton 3 ton, the coils are rated to the compressor. If your coil is too small for your compressor it can make it work harder than usual.
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Old 06-08-2008, 07:37 AM   #6
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Bad compressor, and coil question...


So it makes sense to replace the coil when I replace the compressor to match the rating, but what's the proper way of determining the rating? Any handy sites out there you can recommend? What's the cost of this approximately? Thanks for your help.
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Old 06-08-2008, 10:53 AM   #7
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Bad compressor, and coil question...


Have you lived there for a while and was it cooling the house ok? If it was cooling before you do not need to change the coil when the compressor is replaced.

Make sure that filter dryers are installed that are suitable for burnout/clean up.
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Old 06-08-2008, 11:19 AM   #8
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Bad compressor, and coil question...


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Originally Posted by cjett View Post
Have you lived there for a while and was it cooling the house ok? If it was cooling before you do not need to change the coil when the compressor is replaced.

Make sure that filter dryers are installed that are suitable for burnout/clean up.
Been in the house about 2.5 years. The cooling and heating I would say is rather average, but it's hard for me to gauge because I have no experience on what the adequate performance of this type of HVAC system should be. Would be nice to know how to rate the system based on the size of home and know how to evaluate the HVAC to know if it's the right size/rating. I've also asked around forums for approximate prices on compressor replacement and coil replacement (including what comes with the job like F22, evacuating the lines etc) to have a sense o what to expect (and hopefully not overcharged). So far no luck but I guess prices vary significantly that no one would want to answer???. Thanks for your help. Im in MD and its HOT today.
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Old 06-08-2008, 11:41 AM   #9
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Bad compressor, and coil question...


To know exactly what size unit you need for cooling and heating you need to have a load calac done for your house. Most times a HVAC contractor will not give you the numbers needed until you have signed a contract with them, if you can even find a good company to do one. They do not want to spend the time and expense to do one and then the HO give the size to another contractor with a lower bid.

You can do your own for less than 50 with this software.

http://hvaccomputer.com/talkref.asp
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Old 06-08-2008, 07:12 PM   #10
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Bad compressor, and coil question...


A shorted compressor will show 0 or infinite ohms. The way to test for a short to ground is remove the compressor leads and and with your ohm meter test each spade c s r to a good ground. The readings you are coming up with seem normal for the compressor windings around 1.5
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Old 06-08-2008, 07:22 PM   #11
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Bad compressor, and coil question...


I just looked through your pics. You can not determine the size of a coil by its fisical dementions. the coil should have a model number somwhere and that will tell the size. 12=1 ton 24=2 tons 36= 3 tons 48= 4 tons etc etc. one of these numbers will be represented in the model #. Kepping in mind 12000 btu's = 1 ton.
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Old 06-08-2008, 07:44 PM   #12
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Bad compressor, and coil question...


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Originally Posted by ridgevilleac View Post
A shorted compressor will show 0 or infinite ohms. The way to test for a short to ground is remove the compressor leads and and with your ohm meter test each spade c s r to a good ground. The readings you are coming up with seem normal for the compressor windings around 1.5
Whoa...wait a minute.. I must have had a brain fart. I thought that 2.3Ω was close enough that it would be the same as being zero. So you're telling me that any resistance in the compressor windings would indicate a working compressor? Thats what I did, I followed the wires out from the compressor and disconnected them (small gauge red, black, brown). There where 2 other black wires but they went to the board. The readings look normal? Ok now I'm back to square one. What could possibly be causing the breaker at the main box (whole house breaker box) to trip when I try to use the cooling?

Last edited by Undepelo; 06-08-2008 at 07:46 PM.
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Old 06-08-2008, 07:50 PM   #13
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Bad compressor, and coil question...


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Originally Posted by ridgevilleac View Post
I just looked through your pics. You can not determine the size of a coil by its fisical dementions. the coil should have a model number somwhere and that will tell the size. 12=1 ton 24=2 tons 36= 3 tons 48= 4 tons etc etc. one of these numbers will be represented in the model #. Kepping in mind 12000 btu's = 1 ton.
Well based on your clarification I'm thinking at this point its a mute point.. If the compressor is working all I want to do is get it to stop tripping the breaker and work like its supposed to. Hopefully with some more pointers I'll be able to troubleshoot this and stop my family and I from sweating like Tour de france cyclists.
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Old 06-08-2008, 08:01 PM   #14
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Bad compressor, and coil question...


Yes resistance in the compressor winding is telling you that the windings are good (TO A POINT). A shorted compressor will be to ground. With the leads off of the comp. Take your ohm meter and place the red probe on c terminal and place the black probe on any good known ground. all unpainted screws should be a good ground source. Check all 3 terminals and report your findings. Mike
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Old 06-08-2008, 08:13 PM   #15
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Bad compressor, and coil question...


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Originally Posted by ridgevilleac View Post
Yes resistance in the compressor winding is telling you that the windings are good (TO A POINT). A shorted compressor will be to ground. With the leads off of the comp. Take your ohm meter and place the red probe on c terminal and place the black probe on any good known ground. all unpainted screws should be a good ground source. Check all 3 terminals and report your findings. Mike
What I did was measure the resistance across pairs of all three, ie red and brown, then red and black, then black and brown. The black and brown gave me the low ohm reading I though would indicate a shorted compressor. I read it's good if it's zero and bad if there was low resistance between them. I did remove the red/black from the switch block and the brown from the capacitor. BTW the system has been switched off for a while, and I know capacitors discharge eventually, but I read no voltage across the terminals of the capacitor. Is this normal?

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