I am servicing my 85 300SD A/C system (with virgin R-12). Besides doing a vacuum pull to remove moisture and check for leaks (with a Welch 1397 pulling a whopping 17.7 cfm ), I want to do a pressure test to test for leaks. I've seen that many people do it with Nitrogen and a little R-22, but I don't have a Nitrogen tank laying around and don't want to buy or rent one if it is not necessary.

I happen to have a full 40 cf tank of Argon/CO2 for my MIG welder and a load of spare gas fittings that I could work onto the manifold. I also happen to have three fully functional military surplus explosion proof noble gas detectors (Argon, Neon, Helium). You can get your own here: http://cgi.ebay.com/Phase-1-Instruments-Leak-Detector_W0QQitemZ130015628605QQihZ003QQcategoryZ53298QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

These detectors were designed to test fuel tanks and lines on airplanes without having to completely remove the fuel residue - simply presurize with a noble gas and sniff for leaks. I figure since they test for Argon, I could presurize my A/C system without having to add the R-22 and using my refrigerant sniffer.

Can anybody think of any downsides to this?

Also, how much pressure should be sufficient to pressure test a system? How much pressure do people use when checking with Nitrogen?

Many thanks

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