Volkswagen Passat 1995 Official Factory Repair Manual page 4105

A/C refrigerant system, notes
http://ebahn.bentleypublishers.com/vw/servlet/Display?action=Goto&type=repair&id=VW.B4.HA01.87.1
R-134a refrigerant oil
A special Polyalkylene Glycol (PAG) synthetic oil
is used in R-134a systems. This oil is NOT
compatible with mineral based oils used in R-12
systems.
CAUTION!
Refrigerant oils used for the R-134a system
and R-12 system are NOT compatible. Use
only the specified synthetic oil for the R-134a
refrigerant system. DO NOT use R-12 system
oil in an R-134a system or R-134a system oil
in an R-12 system. If the refrigerant oils are
mixed, system contamination will occur and
compressor failure may result.
R-134a refrigerant system oil (PAG oil)
absorbs moisture very rapidly. Moisture
combines with the refrigerant to form acids
which will damage the system. Use only the
specified oil from a sealed container and
ALWAYS reseal oil container immediately
after use. DO NOT use oil if it has become
contaminated with moisture or if container
has been left open..
Do not allow refrigerant oil to come in
contact with engine oil or transmission fluid
(for example when disposing). Dispose of
used PAG refrigerant oil separately following
laws governing hazardous waste disposal.
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