High Pressure Relief Valve
WARNING: This page is about a different car, the 2002 Mercury Villager. However, it is still accessible from the selected car via links, so may be relevant.
High pressure relief valve is located on compressor manifold. To prevent damage to compressor and other A/C components, relief valve will open when pressure increases to about 550-600 psi (38.7-42.2 kg/cm2 ).