Expansion Valves: The expansion valve is a complex valve which regulates refrigerant flow at the evaporator inlet with an internal moving rod mechanism. This rod opens and closes to differing heights based upon the cooling burden put upon the system. This process of metering modulates the flow according to the temperature of the refrigerant in the evaporator coil. Too much refrigerant could cause the evaporator to get too cold and even freeze up the coils. Too little refrigerant would result in inadequate cooling.
The refrigerant which enters the expansion valve is high-pressure liquid, and is warm. The liquid which flows through the valve and enters the evaporator is low-pressure and cold. This is the exact point where the refrigerant has passed from what is known as the “high side” to the “low side” of the system.
Unlike the expansion valve, the orifice tube is a simple fixed device with no moving parts. It therefore cannot vary the flow of refrigerant into the evaporator, but rather causes a permanent restriction in the system. However, like the expansion valve the orifice tube regulates refrigerant flow through the system and filters debris which may come through in its screen.
It becomes necessary to replace the orifice tube if the fine mesh screen or the internal components of the orifice tube become plugged, restricting refrigerant and lubricant flow. Orifice tubes also designate the dividing point between the “high” and “low” sides of the system.