The Nissens AC Expansion Valve - 999231 is a component used in automotive air conditioning systems. It is responsible for regulating the flow of refrigerant into the evaporator, which cools and dehumidifies the air inside the vehicle. This valve is designed to fit specific makes and models of vehicles and is made with high-quality materials for reliable performance. It is an essential part of the AC system and helps maintain a comfortable and consistent temperature inside the vehicle.