High Pressure Relief Valve
WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
The A/C system is mechanically protected with the use of a high pressure relief valve, located in rear of compressor. If refrigerant discharge pressure exceeds 455-525 psi (32.0-36.9 Kg/CM2 ), high pressure relief valve opens, venting refrigerant to prevent system damage.