For 1990-2009 cars

The compressor is equipped with a pressure relief valve, which acts as a mechanical safety device. Under certain conditions, refrigerant pressure on the compressor discharge side may exceed the designed operating level. In order to prevent system damage, the valve is designed to open automatically at approximately 3171-4137 kPa (461-599 psi). This will vent the refrigerant to the atmosphere. Fix any condition that causes this valve to open incorrectly. Replace the refrigerant oil and the refrigerant as needed.