The MrCool 3 to 5 Ton Thermostatic Expansion Valve is a component in refrigeration and air conditioning systems that controls the amount of refrigerant flow into the evaporator thereby controlling the superheating at the outlet of the evaporator. It has also been designed to regulate the rate at which liquid flows inot the evaporator from the condenser. This controlled flow helps to maximize the efficiency of the evaporator while preventing the excess liquid refrigerant from returning to the compressor.