Questions about A/C vacuuming

[cobram at juno.com]

The chances of pulling -30inches with a Venturi type vacuum and slim.  As
another Qlister said, pull vacuum for around 30 minutes, if you have a
good volume commercial compressor, you should be down around -20inches. 
Close everything off and watch the dials.  If after another half hour or
so you're still have the same residual vacuum, then you can fill the
system.  If you lose vacuum, then you have a leak somewhere that has to
be addressed first.

BCNU,
http://www.geocities.com/cobramsri/