In an R-12 system, with 81 degrees ambient temp, I am getting 25/220 PSI lo/high at high idle (2k rpm) with the fan and A/C setting on max. Vent temp. is sub-40's. Compressor doesn't seem to stop.
What do you guys think?
Thanks once again for all of your help. Temp. gauge in vent reads 38-39 F.
Thanks also for the A/C education. I didn't know an A/C system can only drop air about 17-20 degrees MAX.
Hope I get an opportunity to run into you sometime. I definitely owe you a pitcher.
One trick I learned from a refrigeration mechanic friend of mine: after finding all the leaks you can, vacuuming down, verify the system will hold a vacuum overnight.
This is unfortunately no guarantee it'll hold pressure; I've had bad old hoses on a car that would hold vacuum but not pressure.
So then he charges the system up with leftover R-22 from home A/C service (obtained from another friend) and verifies that it will run and hold pressure with the R-22. R-22 will show up on those electronic freon leak-detectors.
Unfortunately, R-22 won't cool in an automotive system, but it will develop pressure.
NOW if the system is leak-free, it should hold R-12.
The method you describe using R22 is illegal unless you recover the R22. Very few auto shops will dedicate a machine for recovering R22.
A better way to use R22 to look for leaks, and a method that is legal, is to use 4 oz. of R22 and then build pressure with Nitrogen, up to about 200PSI. This is enough R22 to show up with a leak detector, and enough pressure to show up even high pressure only leaks. it is then legal to release this small amount of R22 into the atmosphere.
This method is approved by the EPA with the thinking that it's better to allow 4 oz. of R22 into the atmosphere as an environmental trade off against a leak remaining that allows a larger amount of more harmful R12 into the atmosphere.
As far as holding the vacuum, you should ALWAYS do a gross leak check after evacuating the system for a short time, by seeing that it will hold a vacuum for five minutes. If it will hold it for five minutes, it would be rare that it would not hold it overnight. As you pointed out vacuum does not show up leaks that will show up under pressure unless they are significant.