Todd inquired:

 >  Is the low side fitting located right off the
 > compressor?  Where is the high side fitting located on
 > the Rear Air of a 90 Westfalia?

And since I was wondering the same thing... I waited. But no response.
So I had to go and find it on my own....

FWIW, Todd, yes, the low side fitting is right off the compressor. The
high side is a bit hidden (lousy, $%&! Bentley doesn't show WHERE it
is....)

Go in to your cabinet on the left side (the one most convienent from
the rear hatch.) Remove the middle shelf (oh and all other things on
that shelf and below it.). Then remove the two screws holding that
corner section in. You'll need a short phillips for that. You'll find
the high pressure fitting in there (along with a couple of fuses,
relays, connectors and such.)

happy trails. (now to get outta here and off to WV for the weekend.)