Orifice tubes and expansion valves (commonly called Thermostatic Expansion Valves or TXV's) both perform the same function in auto air conditioning systems, they just look a little different. These components provide a restriction in the flow of refrigerant. That restriction causes the refrigerant to change from high pressure liquid freon into low pressure liquid freon before it enters the evaporator.
Typically, expansion valves (TXV's) will be located at the inlet of the evaporator.
Block type valves will have both the inlet and outlet (liquid and vapor) of the evaporator passing through the valve. The conventional design expansion valve will be mounted on the inlet (liquid line) only.
On the other hand, orifice tubes (also called fixed orifice tubes or CCOT- Cycling Clutch Orifice Tube Systems) could have the orifice tube located in a variety of positions. As shown on the right, the orifice tube could be located at the EVAPORATOR INLET, mid way between the EVAPORATOR and the CONDENSER (in-line) or at the CONDENSER OUTLET.
As a general rule, Expansion Valves and Orifice Tubes are serviced by replacement. In some cases, where an expansion valve is manufactured to include an inlet screen, the inlet screen may be removed and cleaned to restore proper flow of refrigerant to the system. Orifice tubes likewise fail because of debris and corrosion being caught up on the inlet screen. However, as they are usually a low cost item, it is generally accepted that they be replaced rather than cleaned, therefore assuring that debris is eliminated from the A/C system.
**sorced from a diff site, but all the info is correct and I didnt feel like typing it all out lol
