Hi,

Converted my A/C from R12 to R134a (Volvo kit) earlier this year. System worked great for a while, then my tranny went out and the car sat for 4 months. After I got the car back on the road again, I noticed that the A/C compressor would cycle constantly, on for 1 second and off for about 4-5 seconds. Cooling was so so. one day the compressor started to make a loud screechin sound and I shut it off and did not use it for a long time.

Lately it's been real hot here in So. Cal. and I thought I would take a look at the problem. My first thought was that when the car sat for 4 months the refridgerant leaked out, so I bought some more R134a and was going to charge the system, however I decided to check the pressure first at the charge port and discovered that the pressure was 150psi! I let enough pressure out so that it read 25 and tried to run the A/C, it stil cycles on 1 sec. and off 4-5 sec. but provides absolutely no cooling...

Any ideas/suggestions what I should do?

Thanks,
JJ

First. The screeching sound when the compressor starts up is the clutch slipping. Bad news.

Second. When you check the pressure, turn the AC on first! Otherwise the pressure will always read high, this is normal. Your system kicks the compressor on when it reaches 25-27 psi and turns off at about 18psi. Add a can of r134a and you will get cold air. Make sure the can has coolant in it by shaking it at the store. I got an empty can once without realizing it and nothing happened when I "added" it to the car. Baffled me for about 2 days.
--
95 854T, 88 780, 88 245, 01 A4 Audi

Thanks for your reply. ok, so my compressor or clutch may be bad then?

I did start the engine and turned the A/C on to see what the pressure reading was, and when the compressor cycles on the pressure drops to about 20psi, then when the compressor is off for 4-5 seconds the pressure builds back up to about 40. Does that sound normal?

Thanks,
JJ

I recall that at 70 or so outside you should get something in the range of 90 lbs of pressure with the system standing still. Refrigerant expands greatly with heat, however, so at 90 ambient I wouldn't have a clue as to what you could expect--one fifty might not be unrealistic with the higher-running R-134a.

I have a sneaking feeling that there was some of the old R-12 still in the system. It can hide in the oil and leach out over time. When R-12 and R-134a are combined they make an azeotropic--I may have the spelling wrong--gas, i.e. one whose pressure when heated runs higher than either of the combinants. My recommendation is to evacuate the system and be sure it is held at a vacuum for an hour or so after you have it as low as the vacuum pump will take it. That should remove all of the old refrigerant and any moisture present. Then add some oil and recharge with two cans of R-134a.

Good luck.

-Steve