Expansion Valve

The expansion valve is adjustable
and controls the freon flow through the system (and the pressure difference between the two sides). The inlet side of the valve is at high pressure and the freon is a room temperature liquid at this location. In the expansion process, the pressure drops rapidly to the low pressure value

Diagram from: Sears, "Thermodynamics," Addison Wesley (1953)

and the freon is superheated in this new pressure condition.The material then undergoes a partial change of phase, using its internal energy to provide the heat of transformation from the liquid to vapor phase. The reduction in internal energy is associated with a decrease in temperature of the two phase material exiting from the expansion valve.