Expansion Valve: Description and Operation

A/C EXPANSION VALVE
The "H" valve-type thermal expansion valve is located in front of the heater-A/C housing between the liquid and suction lines and the evaporator coil.

The expansion valve is a calibrated unit and cannot be adjusted or repaired. If faulty or damaged, the expansion valve must be replaced.

High pressure high temperature liquid refrigerant from the liquid line passes through the expansion valve orifice. The refrigerant is converted into a low-pressure, low-temperature mixture of liquid and gas before it enters the evaporator coil. A temperature sensor in the expansion valve control head monitors refrigerant temperature leaving the evaporator coil through the suction line. The valve adjusts the orifice size at the liquid line to let the proper amount of refrigerant into the evaporator coil. Controlling refrigerant flow through the evaporator ensures that none of the refrigerant leaving the evaporator is in a liquid state, which could damage the compressor.