Expansion Block/Orifice Tube: Description and Operation

NOTE: The A/C evaporator core orifice should be replaced whenever an A/C compressor is replaced.

The A/C evaporator core orifice has the following characteristics:
- is color-coded red
- has a diameter of 1.57 mm (0.062 inch)
- is located in the discharge tube
- has filter screens located on the inlet and outlet ends of the tube body

The A/C evaporator core orifice is the restriction in the refrigerant circuit that creates the pressure drop necessary for cooling by metering the flow of liquid refrigerant into the A/C evaporator core, which reduces the pressure.

Operation is as follows:
- The temperature of the A/C evaporator core is controlled by sensing the pressure within the A/C evaporator core with the A/C cycling switch.
- The A/C cycling switch controls compressor operation as necessary to maintain the pressure in the A/C evaporator core within specified limits.
- The inlet filter screen acts as a strainer for the liquid refrigerant flowing through the A/C evaporator core orifice.
- O-rings on the A/C evaporator core orifice prevent the high-pressure liquid refrigerant from bypassing the A/C evaporator core orifice.
- Adjustment or service cannot be made to the A/C evaporator core orifice assembly. It must be replaced as a unit.
- The same A/C evaporator core orifice is used for all A/C equipped vehicles with or without an auxiliary A/C system.