Morphing Air Conditioner into Autocascade System

[mytekcontrols]

You're expecting to condense ethan or ethylen with respectively R600a or R290? Good luck
Considering they won't blend (I'm not sure they won't...) :
R170 is the hardest mid range second stage refrigerant (~-85°C @ 1bar like R23 and R13) to condense because of very high latent heat of vaporisation. A R600a compressor must have 65% greater displacement than needed with R12 to get the same capacity, so don't expect to remove the heat of R170 to condense it at decent pressures.

Actually I think I can condense it at reasonable pressures with only R-600 (43 suction/240 discharge):

First Test Results (-102.6C @ 125 Watts)

And with R-123+R-22 (49 suction/275 discharge):

-101C @ 150 Watts Applied Load

On a similar note, could you get away with strictly R290/R1150 or should you keep the R600 loop for compressor cooling and as a way to help purify the R1150 by having 2 loops to pull the R600/R290 components out of the mix?

I think it best to use both the R600 and the R290 for the reasons that you stated in the end.

Edit: I'll be running my next test with R600 and R290.