Volkswagen Passat 1995 Official Factory Repair Manual page 4103

A/C refrigerant system, notes
http://ebahn.bentleypublishers.com/vw/servlet/Display?action=Goto&type=repair&id=VW.B4.HA01.87.1
Effects on metal
In its pure state, refrigerant R-134a is chemically
stable and will not attack iron or aluminum.
However, the mixture of R-134a and PAG oil
may deteriorate certain metals (copper) which
could lead to blockage, leaks or deposits on the
compressor piston. Therefore, when making
system repairs, use only genuine Audi
replacement parts which are specified for use
with R-134a refrigerant.
Water solubility
Liquid R-134a refrigerant will absorb only very
minute quantities of moisture. However, R-134a
vapor can absorb large amounts of moisture.
Water in the system forms ice in the expansion
valve or restrictor causing the system to stop
cooling. In addition, moisture combines with the
refrigerant to form acids which will damage the
system.
Toxicity
Refrigerant R-134a is non-toxic up to a
temperature of 101 C (214 F) and is safe
when handled and used properly.
Above 101 C (214 F), gas pressure is above
39.5 bar (573 psi) and R-134a begins to
decompose into poisonous gases (hydrogen
fluoride, carbonyl fluoride and fluorine). These
gases give adequate warning of their presence
since they cause irritation of the mucous
membrane (throat).
Refrigerant R-134a gas has no effect on
foodstuffs; it does not poison food or make it
inedible.
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