This expansion valve meters the flow of liquid refrigerant into the evaporator coil of the air conditioning system. It sits on the evaporator inlet, where it maintains a pressure differential that controls the refrigerant's evaporation rate. A failing valve can cause insufficient cooling or a complete loss of system pressure. The valve is designed for use with R12 refrigerant. On installation, ensure the O-rings are replaced and the system is evacuated and recharged to the manufacturer's specification.