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mrgadfly 06-30-2011 12:49 PM

Do I really need a new compressor, or am I about to be ripped off?
I had a local HVAC tech check my HVAC out. He was outside a short time, came back in and said I needed a new compressor. I said I'd have to talk to my wife to see if we had the funds.

I thought he was out there for REALLY short amount of time, something like 10 minutes. I wondered if he really checked anything at all. So, I got to reading this forum and a few others, and I did some testing and checking myself, and I don't think the compressor is bad at all--assuming I did the checking and testing right.

I swapped the thermostat with another identical thermostat on another system, and both thermostats work on the other system.

As the contacts on the contactor were burned and had a small patch of black soot surrounding each contactor, I replaced it with a Mars2 17311 24 volt Contactor Relay, 1 Pole 30 Amp. The compressor still didnít run. It seems like, if the original contactor were actually bad, this should have taken care of it, but it didnít. However, the compressor does come on if I push in the contact button in the center of the Mars2 contactor.

This Mars2 contactor seemed a little light and not as heavy duty as the original one (donít know info on label as it was faded), so I thought Iíd get another one that seemed to look and feel a little more like the original one. I am replacing it with a Cutler-Hammer C25CNB130T Contactor , 30 Amp , 1+ Pole , 24 VAC Coil C25CNB130T.

In the mean time, does anyone have any suggestions as to what else I should test and how?

Interestingly, on another forum, one reply said a compressor could be found to be bad in 10 minutes, but he didn't address the ohm readings I took. If I took them right they were as listed below. If understand the compressor ohming procedures correctly, the ohm reading from the COMMON terminal to START terminal and the ohms from the COMMON terminal to the RUN terminal, when added together should equal the ohms reading from the RUN terminal to the START terminal. They seem to as noted below.

The information on the data plates is as follows:
Payne compressor assembly
Model# PH12NA0204-A
Serial# PH12NA024000AAAA

Copeland Compliant Scroll Compressor
Model# ZR22K3-PFV-230
Serial# 99D3989AL

Compressor ohms:
C-S = 1.9 ohms
C-R = 1.1 ohms
R-S = 3.0 to 3.1 ohms (meter kept fluctuating)

Capacitor uf readings as listed on label:
7.5 uf (the lower reading is the fan I believe?)
40 uf

Capacitor readings as tested from C-Fan and C-Herm:

Fan motor ohms :
Brown-Yellow = 56.2 ohms
Brown-Black = 44.6 ohms
Black-Yellow = 32.7 ohms

Thank you all again for any help or clarification.


hvactech126 06-30-2011 05:04 PM

check for 24v to coil side of contactor..... You said if you push it in the system runs, well if your stat is set to cool and calling for compressor that will pull in the contactor if the it has 24v to the coil of the contactor.

Marty S. 06-30-2011 05:14 PM

Ohms look good and since it ran with the contactor pushed in it's not shorted internally. Could be a mechanical failure inside the compressor or it could be he misdiagnosed the problem. Call the company up and ask why the compressor was deemed to be bad.

beenthere 06-30-2011 09:00 PM

If the contactor isn't pulling in. You need to see where your losing the 24 vols.

clocert 07-01-2011 09:25 AM

What was the problem to begin with ? Did your AC stop working ?

biggles 07-01-2011 06:42 PM

call the cooling from the stat check for 24vs on the pair of low voltage wires going into the compressor...should have it there...see if you have a low or hi pressure switch might be open..find the hot R wire to get the contactor to pull in from the stat...trace the contactor 24v wire back from its slip clip..some thing is open...

Artco 07-01-2011 10:21 PM

Also see if you have a condensate pump safety switch or aux drain pan safety switch, they may be holding the low voltage circuit open.

Ac_Repair 07-02-2011 12:51 PM

San Antonio ac repair
I have had the same problem with my mothers central air unit. the compressor comes on when you push the contactor in. If you know for a fact that your thermostat is working properly and you hear the unit or the blower fan come on, try replacing the start capacitor. you will have to look at the schematic which should be inside the cover that you removed to see the contactor.

If you hear your compressor come on and begin to build pressure it probably is not your compressor which is faulty. I have replaced these on several units for friends, that part unsually cost around 30 bucks and is very simple to replace. It will probably cost you less than a service call.

I cant remember which, but these are a couple of the sites that I used to find out how DIY ac repair.

beenthere 07-02-2011 05:01 PM

Ac repair. You must actually give DIY repair advise to be allowed to have links to your company in your signature. Don't try to fool our members into thinking your a DIYer, and then post links to your company.

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