Engine Size: 250
Refrigerant Type: R12
Ambient Temp: na
Pressure Low: na
Pressure High: na
As I stated in previous posts, I bought this car in October, 2010 and noticed that the A/C wasn't cooling. When I got the car home, I pushed in the Schrader valve and saw no refrigerant. I pulled a vacuum and when it held for one hour, I charged in R12. The A/C immediately cooled to 42 degrees. I alternate driving a 2008 Chevrolet with this car and in October, 2011, I found once again that the A/C wasn't cooling. A check of the Schrader valve confirmed a loss of refrigerant. I again pulled a vacuum and found that the vacuum wasn't holding. After several hours the vacuum was gone. Members of this board suggested an input shaft seal leak and I installed a rebuilt A6 compressor in May of this year. The system held vacuum for hours so I charged in R12 and the A/C cooled to 45 degrees while driving and 38 degrees with the car idling in the garage.
I last drove this car in September and Monday it was time to change cars. As I was backing up out of the garage, I turned on the A/C and felt no cooling. It was a hot day and I really missed the cold air coming out of the vents as I drove along the highway. When I installed the new rebuilt compressor in May, I added UV dye to the oil. Back in the garage I took out the UV test light and checked the hoses, expansion valve, condenser, drier, and compressor for any UV dye. I didn't see any so I got out the Robinair 15600 vacuum pump and pulled a vacuum. I got 29 inches and left it overnight. The next morning the gauge still read 29. The only thing I could do next was pressurize the system with nitrogen. I could only pressurize to 150 psi but I immediately heard hissing that was coming from the fitting connecting the high pressure hose from the compressor to the condenser. I shined the UV light and saw dye at the fitting. I put wrenches on both sides and found that the nut was loose. I disconnected this fitting and found that the O ring was also damaged. I replaced the O ring, tightened the fitting, and pressurized to 150 psi. The system is holding with no leaks and tomorrow I will pull a vacuum. I won't charge in any refrigerant because I only have enough R12 for one more recharge. It is now cold and overcast so I probably won't need A/C until next year.
I bought a 30 pound jug of R12 from Kragen for $120 back in 1994 before it was banned. I thought I had enough to last me for the rest of my life. I should have listened to a co-worker who told me he was buying two jugs and that I should buy two as well.
Edited: Fri October 19, 2012 at 10:11 PM by Scratch
Sounds to me like you found the leak, good luck to you.
As you know now, always pressure test R-12 systems before charging. Some leaks hold vacuum but leak under pressure. It's good that you didn't exceed 150 psi because that is about the limit before the evaporator is prone to blow out.
Thank you cussboy and mk378. Unfortunately, I celebrated too soon. After replacing the damaged O ring and tightening the nut, the system held 150 psi for a few hours. But a gradual leak has developed and I find myself right where I was in April when the system would not hold a vacuum. That leak was also gradual and turned out to be the compressor. I sure hope it's not the rebuilt compressor because it only had a ninety day warranty.
If you havee an electronic sniffer, pull a vacuum amd put an oz of r12 in it. Then put 80 to 90 psi of N2. you should find the leak. Put a plastic bag around the compressor for a few hrs. Then stick the sniffer in there and see if you have an alert.
Thank you Dougflas. I don't have a sniffer so I'm going to try and eliminate the compressor by removing it and pressuring the system. If the system holds pressure, the culprit will be the compressor. I have the original compressor and will have a steel plate welded onto the rear part that has the inlet holes. I will then install this test jig onto the steel block that has the two pipes. I wonder if I might have caused this gradual leak when I pressurized the system to 150 psi.
In an attempt to find a suspected leak, I had a machinist make a block so I can pressurize the a/c compressor out of the car. What I would like to ask the a/c experts on this board is how many pounds pressure should I pressurize the compressor to and how long should the pressure hold to definitively assert that the compressor is gas tight? I will be using nitrogen gas to pressurize the compressor.
You would need to use a trace gas in there with the nitrogen that the sniffer can detect if it's a slower leak. That way you can pinpoint the leak e.g a shaft seal, or O-ring but
if your going to re-seal the compressor might as well change all seals. Most people do Pressure tests on the system at 300 PSI, so that would be a good Idea if you like.
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