sorry if you think my answer was flippant. not trying to be. just warning you and others about the damage shop air can do to the internals of a system.
I would use 134a if no dry nitrogen was available. CO2 would also work.
if you have a large tank, and some good filters on your air line, the oil may not be a problem, but the moisture would be. be sure you evacuate well.
I did give some good info on the frozen lines.
sorry again if you thought my response was flippant.
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!