Expansion Valve: Description and Operation

Evaporator Unit and Expansion Valve
High pressure liquid refrigerant is delivered to the expansion valve which is the controlling device for the air conditioning system circuit. A severe pressure drop occurs across the valve and as the refrigerant flows through the evaporator it picks up heat from the ambient air, boils and vaporizes. As this change of state occurs, a large amount of latent heat is absorbed. The evaporator is therefore cooled and as a result heat is extracted from the air flowing across the evaporator. The refrigerant leaves the evaporator, on its way to the compressor, as a low pressure gas. An evaporator sensor measures the air temperature at the evaporator and engages or disengages the compressor clutch to prevent icing of the air ways.