An expansion valve is a piece of equipment that reduces pressure in a system. The most common form of these valves is a thermal expansion valve , which is used in heating, ventilation, and air conditioning (HVAC) systems. The two main types of air conditioner expansion valves are thermostatic expansion valves and capillary tubes.
A thermostatic expansion valve controls the flow of refrigerant and can function at various temperatures or pressures. The capillary tube is responsible for transmitting the pressure levels in the system to the sensing tube attached to the TMV and basically acts as a throttle. An air conditioning unit has three main parts: the compressor, condenser, and evaporator. This valve is part of the evaporator.
To cool a building, refrigerated gas, such as Freon®, runs through the compressor where it becomes hot and pressurized. The gas then runs through coils that cause the heat to dissipate, which condenses it back to a liquid. The condensed liquid then runs through an expansion valve where it evaporates and becomes a cold gas, which pulls heat from the surrounding air. The gas runs through another set of coils, and a blower blows the cold air inside the building and the heat that was generated during the process is vented to the outside. A refrigerator or freezer works in the same manner.