A/C Pressure Relief Valve
WARNING: This page is about a different car, the 2002 Lincoln Blackwood. However, it is still accessible from the selected car via links, so may be relevant.
An A/C pressure relief valve is incorporated in compressor A/C manifold and tube to relieve unusually high refrigerant system discharge pressure buildups. See SPECIFICATIONS . It will prevent damage to compressor and other system components. It will avoid total refrigerant loss by closing after excessive pressure has been relieved.