Volkswagen Passat 1995 Official Factory Repair Manual page 4172

A/C refrigerant system, servicing
http://ebahn.bentleypublishers.com/vw/servlet/Display?action=Goto&type=repair&id=VW.B4.HA01.87.5
Fig. 4 Pressure relief valve, checking
Function: Protects the refrigerant circuit from
over-pressure.
Refrigerant oil deposited on rear of compressor
indicates pressure relief valve has opened to
release pressure -arrow-. An adhesive plate is
pushed out.
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12/7/2004