The Nissens AC Expansion Valve - 999221 is a component used in automotive air conditioning systems. It is responsible for controlling the flow of refrigerant into the evaporator, which allows for the cooling process to occur. This valve is designed to regulate the pressure and temperature of the refrigerant, ensuring efficient and effective operation of the AC system. It is made of high-quality materials and is compatible with various makes and models of vehicles. This product is essential for maintaining a comfortable temperature inside the vehicle during hot weather.