I am going to say this again and I will keep saying it untill all you jackseed a/c techs get it through your head... test for leaks UNDER PRESSURE, DO NOT TEST FOR A LEAK IN A VACUUM, AND DO NOT VACUUM A SYSTEM UNTIL YOU ARE SURE THERE ARE NO LEAKS!!!
reclaim the original charge. or if it's already empty... YOU KNOW THERE IS A LEAK! pressurize the system with nitrogen and VERIFY IT DOES NOT LEAK OUT. if it does find the leak before you try and evacuate. look for oil stains, look for bubbles, but LOOK!
evacuating a unknown tighness system is just asking for the lines to acid fail. moisture from the air mixed with oil and refrigerant will turn into an acid and eat your seals and lines from the inside out.

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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!