the mig gas is perfect for both flushing and pressure testing.
nitrogen is CHEAPER than Ag/CO2, and it's moisture free. that's the only reason it's preferred.
I have started using Liquid CO2 supply as a flush gas, I've got this COOL little tank with a blow gun attachment. works great, and I charge it up at my Restaurant customers!!! FREE REFILLS!

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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!