Expansion Block/Orifice Tube: Description and Operation

Expansion (Orifice) Tube:

EXPANSION (ORIFICE) TUBE DESCRIPTION

IMPORTANT: The presence of small amounts of debris or metal chips in the expansion tube is considered a normal condition.

The plastic expansion (orifice) tube (2) is made of a mesh screen (1) and an orifice (3). The expansion (orifice) tube is located in the evaporator inlet pipe at the liquid line connection. The tube restricts the high pressure liquid refrigerant in the liquid line, metering the refrigerant flow to the evaporator as a low pressure liquid.

The expansion tube and orifice have filter screens which protect the refrigerant from contamination on both the inlet and the outlet sides of the tube. The expansion tube is sealed inside the refrigerant pipe by an O-ring. This O-ring is necessary for proper operation of the refrigerant system. When the engine is shut OFF and the A/C has been running, the refrigerant in the system flows from the high pressure side of the tube to the low pressure side until the pressure is equalized. This may cause a faint hissing sound for 30-60 seconds, after the vehicle has been turned OFF, and is a normal condition.