Expansion Block/Orifice Tube: Description and Operation

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.