Expansion valve:



Orifice tube:



The expansion valve has little springs and valves in it which can fail, get clogged up, etc. The Orifice tube is just a fixed hole in a tube. It'll still stop up but it has no moving parts.

An Orifice tube system also needs a "accumulator drier" which is kind of a reservoir for the refrigerant so it doesn't get "backed up" in the system due to a non adjustable orifice. The receiver/drier on an expansion valve system is also a type of reservoir but the expansion valve keeps pressures from building up too high.

This is the way I understand it. Someone correct me if I'm wrong or fill in the blanks.

An expansion valve system also has the compressor running all the time when cooling with the valve preventing the evaporator from freezing and maintaining proper pressures.

An orifice tube system cycles the compressor on/off via an electric switch to contend with freezing and maintaining pressures.

Someone else who actually knows something want to weigh in?

My car's expansion valve has an "equalization tube" in addition to the bulb:



Not sure what it's function is but most expansion valves don't seem to have one...

Orifice tube:

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD