Volkswagen Passat 1995 Repair Manual page 29

A/C refrigerant system, notes
http://ebahn.bentleypublishers.com/vw/servlet/Display?action=Goto&type=repair&id=VW.B4.HA01.87.1
CAUTION!
R-12 and R-134a refrigerant are NOT
compatible. Never add R-12 refrigerant to an
R-134a system or R-134a refrigerant to an R-
12 system. If the refrigerants are mixed, total
system contamination will occur and
compressor failure may result.
Refrigerant oils used for the R-134a system
and R-12 system are NOT compatible. Use
only the specified synthetic oil (Polyalkylene
Glycol/PAG) 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.
Immediately plug open connections on A/C
components to prevent dirt and moisture
contamination. Likewise, DO NOT remove
new component from packaging until ready
to install. Immediately tighten component
connections after installation.
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12/7/2004