Hi pc ice. I understand that R-134A is mixed with R-23 to help oil miscibility, but other than that... could you explain why you add R-290, or anything else to the refrigerant charge?

R-13 has a saturation temperature of about -90F to -100F (without a P/T chart in my hand) at atmospheric pressure, whereas say R-404A has a saturation temp of about -50F.

How would one determine the actual characteristics of a proposed blend of refrigerants?