GM Genuine Parts A/C Orifice Tubes are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These tubes, which separate the high and low pressure sides of the air conditioning system, control the flow of low pressure liquid refrigerant into the evaporator. The orifice tube is essentially a calibrated restriction located at the inlet to the evaporator. This causes the necessary pressure drop to allow the liquid refrigerant to evaporate within the evaporator and absorb heat. Since the orifice tube is fixed, the system is regulated by either cycling the compressor clutch or by a variable displacement compressor. GM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE).