Pressure Relief Valve
WARNING: This page is about a different car, the 2004 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.
The refrigerant system is also protected by a pressure relief valve, located in the rear head of the compressor When the pressure of refrigerant in the system increases to an abnormal level [more than 2, 990 kPa (30.5 kg cm2, 433.6 psi)], the release port on the pressure relief valve automatically opens and releases refrigerant into the atmosphere.