Pressure Relief Valve
WARNING: This page is about a different car, the 2001 Volkswagen EuroVan, 2000 Volkswagen EuroVan, 1999 Volkswagen EuroVan, and 1997 Volkswagen EuroVan. However, it is still accessible from the selected car via links, so may be relevant.
Pressure relief valve is mounted on compressor or receiver drier. To prevent damage caused by excessive pressure, relief valve opens at greater than 580 psi (40.8 kg/cm2 ) and vents excessive pressure into atmosphere. Relief valve closes after pressure is reduced to prevent total refrigerant loss.