Today I went and bought some bottles of propane/butane mix (70%/30%), which I'm going to use for brazing, and I'm also planning on using it as a refrigerant.

As far as I've understood, using a low-pressure gas, will help in condensing a higher-pressure gas, and therefore allowing me to use a weaker compressor and a smaller condensor, than if I only used the higher-pressure gas.

Now, the butane has a boiling point of only -0.5C, whilst, the propane boils at -42C. Do you guys think using butane as an auxiliary condenser (proper term?) for propane will help much?

I've also found this mix of propane, butane and isobutane (or, since this is VPCC: R290/R600/R600a). I don't know the percentages here, but I at least know the isobutane boils at -10C. Would this be a better mix?