You put the gauges on both the low and high side but always charge through
the low side... there is a chart for what the pressures should be at any
give temperature for each kind of refrigerant... each system takes a certain
number of pounds of refrigerant... the specs should tell you how many on any
system... if it is custom piped there is a formula for determining the
pounds of refrigerant needed to compensate for any amount of special
piping... the Vanagons should be bog standard... I do not have AC in my
Westy... I have worked on AC & R systems for years and hate them all... It
is no place for Wally mechanics... in refrigeration clean and accurate
count... freon systems are unforgiving of contamination... they get even
with sloppy mechanics