I use the Jetta/Golf Bentley numbers for the pressures.  I then fill the
system until the pressures are right for the ambient air temp of that
particular day.  Works every time for me.  Of course I use Freeze-12 instead
of R-12 because it is much cheaper and I have had alot of good success with
using it and it lasting.

Example 1: 86 Jetta with low R-12 charge.  I charged last summer around the
beginning of summer with Freeze-12.  On an 80 degree day the vent temps were
in the mid to upper 30's!  Tested again this summer, same level of freeze out.

Example 2: '91 Vanagon Carat.  Went the whole 9 yards with a/c conversion,
new dryer, o-rings, etc.  On an 80 degree day I got in the low 50s to high
40s at the vent directly above my head all the way in the front of the van
and it is a dark maroon color.  This summer (after a winter of not being
used) it works the same.

Example 3: Just charged a '86 Westy today (basically just added Freeze-12 to
low R-12 charge).  Has the older style Westy A/C with the SD-508 compressor
on it.  At the vent at 80 degrees ambient temp I got 37 degrees!  I was
blowing up on the back of my neck and almost gave me an ear ache.

I would recommend anyone doing any A/C work to check out Freeze-12.  It is
around $8-9 a can, no propane to blow you up, and it works excellent.  I plan
on posting some more A/C info on my web page soon so keep an eye there.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16
Phone: (856)-765-1583
Shop:   (856)-327-0027
Fax:     (856)-327-2242