Expansion Block/Orifice Tube: Description and Operation

EXPANSION (ORIFICE) TUBE DESCRIPTION

The plastic expansion tube contains a fixed diameter tube. The tube has a mesh filter screen at either end. The expansion tube is located in the evaporator inlet pipe. The expansion tube creates a restriction to the high-pressure liquid refrigerant in the liquid line. The flow of the refrigerant is then metered to the evaporator as a low-pressure liquid. When the engine is turned OFF while the air conditioning is operating, the refrigerant in the system continues to flow. The refrigerant flows from the high-pressure side of the expansion tube (orifice) to the low pressure side until the pressure is equalized. The equalization may be detected as a faint sound of liquid flowing (hissing) for 30-60 seconds. This is a normal condition. You may not need to replace the expansion tube when the system diagnostics indicate a restricted expansion tube. Remove the following materials found on the screen with compressed air:
^ Metal chips
^ Metal flakes
^ Metal slivers

You may reuse the expansion tube under the following conditions:
^ The plastic frame is not broken.
^ The expansion tube is not damaged or plugged.
^ The screen material is not worn.
^ The screen is not plugged with fine gritty material.