Karl Townsend writes:

If you
pull a vacuum on a properly selected fluid (IPA???) it will boil and
cool. So, all you'd need is a little vacuum pump and a double wall
container sized for a beer can.

If the fluid boils low enough (R134a etc) then you don't even need to pump
it. But that's cheating to vent the refrigerant. This is supposed to be a
closed system other than the crank input and heat output.