The plastic expansion tube, with the mesh screen and orifice is in the evaporator inlet pipe. The orifice tube provides a restriction to the high-pressure liquid refrigerant in the liquid line, metering the flow of refrigerant to the evaporator as a low-pressure liquid. The filter screens on both the inlet and outlet sides protect the expansion tube and orifice from contamination. Service the tube only as a replacement assembly.

When the engine is turned OFF, after the air conditioning has been operating, the refrigerant in the system flows from the high-pressure side of the expansion tube orifice to the low-pressure side until the pressure equalizes. This is detectable as a faint hissing sound for 30-60 seconds. The hissing is normal.

When system diagnostics indicate a restricted expansion tube, replacement of the restricted expansion tube may not be necessary. Metal chips, flakes, or slivers found on the screen may be removed with compressed air. Reuse the expansion tube under the following conditions: