Expansion Block/Orifice Tube: Description and Operation

Fixed Orifice Tube:

Position in the refrigerant circuit
Line between the condenser and the evaporator.

Function
The fixed orifice tube has the following functions:
- Regulating the amount of flow to the evaporator
- Separating the high-pressure side from the low-pressure side

The liquid refrigerant flows under high pressure from the condenser to the inlet side of the fixed orifice tube. Two O-rings prevent the refrigerant from flowing past the fixed orifice tube. Two filters at the entrance and outlet of the fixed orifice tube remove any particles from the refrigerant. The outlet filter has the additional function of further atomizing the refrigerant. Only a quantity of refrigerant commensurate with the pressure can ever flow through the calibrated internal diameter of the fixed orifice tube. As a result the amount of flow through is restricted. The internal diameter of the fixed orifice tube varies according to the required cooling performance of the air conditioning system. The internal diameter can be determined by means of the color of the fixed orifice tube housing and an appropriate color code chart.