A  expansion  valve ( TXV) is used to meter the flow of liquid refrigerant entering the evaporator coil at a rate that matches the amount of refrigerant being boiled off in the evaporator, This is it's main purpose but like all the other metering devices it also provides a pressure drop in the system, separating the high pressure side of the system from the low pressure side.  thus allowing low pressure refrigerant to absorb heat onto it's self.