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Bad compressor, and coil question...

9K views 24 replies 6 participants last post by  randyt58 
#1 ·
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.
 
#2 ·
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)
 
#4 ·
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.
 
#5 ·
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.
 
#6 ·
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.
 
#8 ·
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.:eek:
 
#9 ·
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
 
#12 · (Edited)
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? :eek: 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? :(
 
#11 ·
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.
 
#13 ·
Well based on your clarification I'm thinking at this point its a mute point.:laughing:. 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. :laughing:
 
#14 ·
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
 
#15 ·
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?
 
#16 ·
quote "all I want to do is get it to stop tripping the breaker "

This is not in your previous posts. Think like a service tech. does the breaker trip as soon as it is reset? Is the t-stat calling for cooling? If it is. Can I turn t-stat off and breaker stays on? (Remove the compressor wires from the contactor and try the breaker. With no power going to the comp. this will eliminate or confirm the Comp.) Can I isolate the low voltage wires going to comp. contactor and breaker stays on? Basicly anything in this cond. is subject to trip a breaker. of course the compressor. or the contactor the cond. fan motor, the reversing valve the compressor heater element. You will have to test all componets that run on 240v just like the compressor to find the culprit. I am not going to get into the air handler could be on the same circuit. Make sure this is not the case. There are lots of componets there too. Good Luck, Mike
 
#18 ·
Mike, thanks for your help and patience. I'm not familiar with the components in the system so its taking some time for things to register. The reason I say I want the breaker to stop resetting is because I'm guessing that once I determine what was making it trip, I'll know what's broken. The system was working during winter, there was some time of inactivity during spring and when I placed the thermostat to the cool setting, ambient air was all that came out the of vents. The breaker trips as soon as the thermostat calls for cooling. The handler blower runs with no issues besides a faint humming thats constant even when off. I exposed the electronics of the handler and saw no obvious signs of damage. The handler has it's own breaker switches in the main box so that tells me it's on its own circuit. I'll search the net for a basic diagram of components and with your tips I'll try some more troubleshooting. My fear of tripping the breaker too much was a possible short in the house that could trigger a fire.
 
#23 ·
Sorry..missed the K in your equation.....Why?...Because there is no single phase AC compressor that I know of that has an 1880 ohm winding. Most are in the 3- 10 ohm range. Therefore I suggest you recheck your readings. You have the formula..if the windings do not match up,what does it matter...you have to replace it either way. And if you do, then ensure you replace the capacitor as well.
 
#24 ·
I see. I wasn't aware that the resistance range was supposed to be so low. :eek: I guess at this point I'm going to try and find recommendations on good companies that can service the unit, although I have serious trust issues and won't be comfortable no matter who comes to do the work. :(
Thanks for all your advice and help.
 
#25 ·
Undepelo,
I think I have the same or similar problm.
I am working on a Coleman Mach EL 15k BTU rooftop unit. I violated my normal rule of not waiting a few hours to a day to power up after moving and tipping the unit. When I first turned on, blower and fan working fine. turn to cool and after a few seconds, got the buzz briefly, then only the fans running. I turned to fan only and waited 14 hours then tried again. Now a fuse blows. (wall fuse). Changed fuse, same thing.
After researching, symptoms pointed to the starter capacitor. Took my 3 caps to appliance parts dealer. He checked and confirmed. Will be installing caps later today so will report back my success hopefully.
On the winding resistance... If you think about it, it would have to be a very low resistance. After all, you are basically checking the resistance of a long piece of wire.

Don't give up doing it now! You are almost there. And if you have a bad starter cap, mine was only 8 dollars!

Good luck

Randy
 
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