Originally Posted by funola

I think he may be referring to the danger of oxygen + oil in an ox-acetylene regulator/tanks setup,.......................................
I was wondering if air can be used to do a poor man's "nitrogen" pressure test in a mobile AC system since it is 78% nitrogen. Is there a danger of an explosion with 21% oxygen and refrigerant oil pressurized to 200 psi? Gut feeling WAG tells me no..........................................Granted, some moisture (relative humidity dependent) will be introduced from ambient air, but since the dryer and TXV will be replaced and the system evacuated afterwards, whatever moisture introduced will be removed.