I'll start the ball rolling.

to properly test a refrigeration (A/C) system for leaks you need PRESSURE! it must be in the form of a gas. NO liquid can be present or it invalidates the test.
Standard test gas is Dry nitrogen. CO2 can be used as can any gaseous refrigerant, but refrigerants are NOT legal to vent, so it's not a good idea to use them unless you have recycling equipment.

testing for leaks with vacuum is a ridiculous plan. I know MANY shops and individuals think it's a good way to test for leaks. It is NOT!
on a rigid piped system (home a/c or refrigerators etc) vacuum can and is used to test for leaks as well as moisture presence... but a DIGITAL micron gauge is required for the test.
mobile refrigeration with flex lines, and semi hermetic compressors with a shaft driven compressor simply cannot reliably be tested with vacuum. the rubber will mask a vacuum leak test, and the crank seals will vent moisture into the compressor, and the dryer in short order...

__________________
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 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!