Is my unit bad? RC winding only 0.8 ohms

R-C (Run-Common) winding normally has the lowest resistance, 3-4 times lower than C-S (Common - Start ) and the remaining R-S (Run - Start) resistance is the sum of the other two. 
In other words, quite a big difference in numbers is to be expected. In fact, the values he has measured are almost perfectly matching the winding resistance values listed by Copeland (manufacturer of compressors for Payne) for single phase 208/230V models for <strong>3-ton</strong> (or, rather 38,000BTUs) compressors. The 5-ton (50,000BTUs+) compressors would have the R-C measured around 0.4Ohm or lower.
This difference may not necessarily mean an issue with the compressor because the resistance measurements  of such low values are not always precise and depend on several factors, including even how fresh was the battery is in his Ohmmeter. Also, to be absolutely sure, the compressor needs to be disconnected from all external connections to its terminal block.
All that said, has replacement of the capacitor fixed the problem? I could not grasp from the question what state of (dis)repair the compressor was left in...
Reply to
homeowners
Thank you for your very helpful reply! The history of this unit is that we replaced the dual capacitor in 2010 and it blew out again last week. The technician noted that the capacitor would probably blow again because of the mis-matched ohms. He said the readings across all the windings should be the same.  When it went out again this week we had a second a/c repair company give us their opinion before we sank the money into a new system. The second technician found that the dual capacitor in the unit was from 2010 and was probably a bad capacitor put in by mistake. I am thinking the first technician accidentally put our old one back in since 2010 was when we had the work done. The second technician also found that the disconnect switch was burned up and thought that might have caused the capacitor to blow in the first place. He said the ohm readings on the unit looked fine. We have asked the first company to come out again and replace the broken capacitor but I wanted to have all my facts straight in case they argued that my defective compressor blew out the "new" capacitor that he put in. In my research tonight I found that three-stage units are supposed to have the same readings on all windings and ours is a single stage unit so I think that was where the technician was getting confused. I feel well-equipped to handle any disagreement we might have over the repairs. Thank You!!
Reply to
Anonymous
Also, where can I find a listing of the expected winding resistance values for this unit? I searched everywhere on the Internet and I wanted to be able to reference the information as the manufacturer lists it to back p my argument. Thanks again!
Reply to
Anonymous
My Payne 5-ton compressor is 7 years old. It blew a run capacitor and the service tech told me it might be a defective unit. He measured the R-C winding and it was only running 0.8 ohms. The other two windings are showing 1.5 and 1.7. He said this large difference in numbers meant the unit might be bad. I know nothing so any thoughts would be appreciated.
Reply to
FortWorthGal
The winding resistance readings seemed OK for the single phase (not single stage) unit. Three phase motors are virtually non-existent in residential A/C systems because homes are usually only wired for one phase.  I don't know why he expected a three phase unit unless it is a commercial location.
Anyhow, there could be a number of reasons the capacitor is blown. The starting relay they changed is definitely one of them. But there can be other issues, not necessarily with the motor of the compressor. For example, it could have a hard time starting because of high pressure in the sealed system, and a hard start kit can be installed to help it start. Also, I though it was rather strange that the resistance values looked like those of a motor for a smaller 3 ton unit even though you're certain it's 5. I would look into this.
The resistance values are from Emerson Climate Technologies, Inc. (current owner of the Copeland brand of compressors) Electrical Handbook which I got on CD. I think (but don't quote me on this) that you can register yourself for an account at Emerson's Website and access their Literature section that should also have it. Registration address is here:
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If you can read and post here the nameplate of the compressor with the part number, I can see if I can just copy the relevant table from the book and post it here.
Reply to
homeowners
Thanks for correcting my phase/stage confusion. I think the technician may just not know all his facts. It is a residential unit and says on the plate that it is a single phase. Either that or he was trying to sell me another one. The plate on the unit matches the original invoice I have from when I purchased the compressor. The product number in both places is PA12NA060000 and my invoice describes it as a A/C 12 Seer Teardrop Payne 5 TO but I cant find the 5 ton written anywhere on the unit. 
We installed a "kick start" on the unit also in 2010 but I understand that those can go bad. 
Reply to
Anonymous
Re: Is my unit bad? RC winding only 0.8 ohms full size image
Re: Is my unit bad? RC winding only 0.8 ohms full size image
Yes, that's a 5 ton packaged (meaning outside unit+furnace+air handler) A/C system part number. They can no longer sell anything less efficient that 13 SEER so info on your unit is not easy to come by. I was not able to positively identify the actual compressor but I think this one highlighted on the cutout from the Emerson/Copeland book is very close. This is ZR57xxx, but you can also have a ZR54xxx which would bring the resistivity values up a bit: R-C would be 0.386 Ohm and C-S - 1.12Ohm
Be sure to click on the "original" link next to the picture to see the table in real size.
Reply to
homeowners

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