Drawing Down a Vacuum

[robmaxfli]

Hi all,

Working with a 1992 Buick park Avenue ( an R-12 car) . I took the AC completely apart and bought new everything: compressor , evaporator, Main Hoses, Accumulator , Condenser, O-Rings. I have R-12.
so I finally got everything hooked back together with 8oz. on Oil in the system as well as some UV dye.
Vacume time: Ist set of gauges took it all the way down to 29Hg but it slowly went flat. I tried another set of gauges and the most if will go is 25Hg on the gauge. I turned it off but it in indeed slowly leaking down to zero.

I'm trying to think of the best way to find the source of the leaks. I hate to sacrifice a can of r-12 to locate the leaks.

Any other ideas that you have?

thanks

[webbch]

Standard procedure is to put in a small amount (1 ounce) of R134a (to avoid wasting the precious R-12) and pressurize with nitrogen, then use a sniffer to find the leak. As long as you don't run the compressor with the R134a in, you'll be fine. Once pressurized, sounds like your leak rate is probably high enough that you'll hear the hissing. If it's anything like it was for me on my first system replacement, a wrong size oring may be the culprit.

[GM Tech]

Pull a vacuum and hold test on gage set first (not attached to car) to make sure it is not leaking

[robmaxfli]

I forgot to mention - I changed the vacuum pump (as well as the gauges) for the 2nd reading of Hg. - Autozone rentals

So I checked the current gauge set as suggested above and found that 25 Hg is the most it will pull down to on the gauge (no hoses used). So maybe it is the gauge for the amount of Hg. However , the 25 Hg will hold steady onto itself with no loss of Hg.

I don't have Nitrogen to test with and I do have R12 Mineral oil and dye already inside. How much R12 would be enough to test with if I had to install some?

thanks