K 3500 Truck 4WD V8-5.7L VIN R (1998)
Expansion Block/Orifice Tube: Description and Operation
The plastic expansion tube, with its mesh screen and orifice is located in the condenser outlet pipe in all models except models with rear air conditioning
(RPO C69). Models equipped with rear air conditioning use a Y-shaped junction block in the tube between the condenser and the front evaporator. The
junction block is located near the right side of the radiator support. The expansion tube is located between the junction block and the front evaporator.
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 expansion tube and orifice are protected from contamination by filter screens on both inlet and outlet sides. The tube is serviced
only as a replacement assembly.
When the engine is turned OFF with the air conditioning operating, the refrigerant in the system will flow from the high-pressure side of the expansion
tube (orifice) to the low-pressure side until the pressure is equalized. This may be detected as a faint sound of liquid flowing (hissing) for 30 to 60
seconds and is a normal condition.
When system diagnostics indicate a restricted expansion tube, it may not be necessary to replace it. Metal chips, flakes, or slivers found on the screen
may be removed with compressed air. The expansion tube may be reused if:
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The plastic frame is not broken.
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The expansion tube is not damaged or plugged.
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The screen material is not torn.
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The screen is not plugged with fine gritty material.
