A/C Compressor Pressure Relief Valve
WARNING: This page is about a different car, the 2004 Lincoln Aviator. However, it is still accessible from the selected car via links, so may be relevant.
An A/C compressor pressure relief valve is incorporated in the compressor manifold and tube assembly to prevent damage to the A/C compressor and other system components, and to avoid total refrigerant loss by relieving unusually high refrigerant system discharge pressure buildups.