Expansion Block/Orifice Tube: Description and Operation

The plastic expansion (orifice) tube (2) is made of a mesh-screen (1) and orifice (3). The expansion (orifice) tube is located in the evaporator inlet pipe at the orifice connection. The tube restricts the high pressure liquid refrigerant in the liquid line. This restriction meters the refrigerant flow to the evaporator as a low pressure liquid. The expansion tube and orifice have filter screens which protect from contamination on both the inlet and outlet sides of the tube. When the engine is OFF the refrigerant in the system flows from the high pressure side of the system to the low pressure side until the pressure is equalized. This may be detected as a hissing sound for 30-60 seconds and is a normal condition.