3-stage cascade

[before]

Thanks for your reply Norseman I'm gonna stay with R1150 into 2nd stage Concerning a 4th stage, -161C is little bit too cold because CPU are usually cold-bugged after let's say -135C.

Ok then; I've substituted 2nd stage 8100btu/h compressor by a 17000btu/h. Drop in temperature is very significant: evaporating point into HX 2/3 is now at -102C while 3rd stage running (about -105C to -106C unloaded). This is nearly 10C of gain with a bonus: succion line is now frozen until the ACL.

So; this makes me thinking about how colder will be both HX after replacement of 1st stage 10000btu/h compressor by a 24000btu/h one?

Evaporating temperature of 1st stage is currently -44C while the 2 lowest stages are running. But it'll be significantly lower with a bigger compressor and so will be the evaporating temperature of 2nd stage...

I'm afraid that R14 alone into 3rd stage will be impossible to use. It'll be too easy to condensate... and it might require me to try a mixture of R50/R14... or to use R290 into 1st stage instead of R404a. What do you think about that?