HVAC 092 Automatic Expansion Valve AXV AEV and evaporator pressure should be 

quick review of the importance of saturation and the refrigerant boiling is what absorbs the BTU that is the power of the latent heat. Also review how conditions affect pressures and the elimination of the single pressure myth for the majority of units.
Then at 4:42 I introduce the Automatic expansion valve and how it maintains a constant pressure.
At 14:00 I dissect the automatic expansion valve and how the internal workings.
Automatic expansion valve is abbreviated AXV and AEV
Its also known as a Constant pressure expansion valve.
SCHR news article about Automatic expansion valve
www.achrnews.com/articles/947...
www.achrnews.com/articles/110...
here is an example of different valves and their application.
www.parker.com/literature/Aft...
www.brighthubengineering.com/...