Car High Pressure Relief Valve
Many systems incorporate a high-pressure relief valve as a safety device in the event that pressure inside the system exceeds safe levels. (Some systems use a disc instead of a valve; when a predetermined pressure is reached, the disc will burst.) Most pressure relief valves will close when the system pressure has returned to a safe level. Excessive pressure can be caused by an overheated condenser or an overcharge of refrigerant.
The high-pressure relief valve is usually located on the receiver/drier (expansion valve type systems) or on the compressor. It’s usually mounted in a safe place so that there’s no risk of refrigerant being discharged toward anyone working on the vehicle.
If the high-pressure relief valve opens for any reason, the system will require recharging with refrigerant and compressor oil.