I like to use Ester Oil as it is compatible with both the old mineral oil and
the 134-A.  Early R-134a systems used PAG oil which is really water absorbent
and not compatible with mineral oil either.  Almost everything I read now
about A/C systems, recommends Ester oil.
As far as where the oil goes, my experience has been that in the Vanagon
system, you have about 2 oz in the evaporator (take it down, drain, and
refill), part of an oz in the high side line and the low side line and the
rest in the compressor itself (if the compressor is empty.  I use between 6
and 8 oz in a typical system.  Hope this helps you.

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