Metering devices are used on AC systems to create a restriction that causes the refrigerant to change from a high-pressure liquid into a low-pressure liquid. The most common types of metering devices are the orifice tube and the thermal expansion valve.
Orifice tubes are available in several sizes, and care should be taken when replacing them in order to install the correct one for the vehicle being repaired. Each size of orifice tube is recognized by a unique color. It is wise to always check the orifice tube each time the system is open for repairs to find out if the system is dirty or has foreign materials flowing through it. The dirt or foreign material will get stuck at the orifice tube since it has a
Thermal expansion valves are available in two styles. The standard valve (left) has a thermal-sensing coil that connects to the evaporator core exit line and is typically located inside the duct box. The block- style valve (right) is self-contained and is typically mounted at the entry point of the evaporator core and can usually be serviced without removing the duct
Some manufacturers design the system with the orifice tube near the entry point of the evaporator. This access point typically is accessible with little obstruction or disassembly required. Make sure that the orifice tube is installed with the arrow facing the direction of normal refrigerant
