EXV is a component in an air-conditioning system that controls the rate at which liquid refrigerant can flow into an evaporator. This is accomplished by use of temperature and/or pressure sensing devices that allow the control to calculate a preset amount of superheat in the evaporator. An air conditioning system with a EXV valve is often more efficient than other designs that use TXV (mechanical thermal expansion valve) because it quickly adjusts the system after compressor cycles and it reacts faster according to the variations in the environment.