I am trying to build a system that will allow me to cool a small heat load (say 100 watts) down to -55C, but I also want to be able to have the same evaporator run at 100C and at any temperature between those two extremes with that same 100 watt load. I've made similar systems in the past that will do -30 to +120C with a single stage sytem by adding hot gas bypass to the compressor so that it can run with anything from full load on it to no load on it. I then added a pulse width modulated valve to regulate the amount of refrigerant that goes to the evaporator so when I want to go to higher temperatures I just reduce the amount of refrigerant sent to the evaporator. I don't see any reason I couldn't do this same thing on just the low temperature stage of a cascade system, but wanted to see what others thought before I build something to try this. Thanks for any input.