High Pressure Relief Valve
WARNING: This page is about a different car, the 2005 Dodge Stratus and 2005 Chrysler Sebring. However, it is still accessible from the selected car via links, so may be relevant.
A mechanical high pressure relief valve is used to vent refrigerant from the A/C system to protect against damage to the A/C compressor and other A/C system components, caused by condenser air flow restriction or an overcharge of refrigerant.
On the TRS-090 A/C compressor, the relief valve is located on the compressor cylinder head, which is on the rear of the compressor. On the HS-15 A/C compressor, the relief valve is located on the replaceable compressor manifold.