Pressure Relief Valve
WARNING: This page is about a different car, the 2002 Infiniti I35. 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 3,727 kPa (38 kg/cm2 , 540 psi)], the release port on the pressure relief valve automatically opens and releases refrigerant into the atmosphere.