I am working to replace an R-12 condensing unit on an old (30+ years) chest ice cream chest freezer, size 8ft L X 2ft D X 2ft W.
My dilema is what refrigerant to use for the new condensing unit. R134a is not very efficient at the minus 10degree F that I want to maintain, I believe R404a is too high pressure for the existing evaporator and tubing. I am thinking about going with 401a unless I can get some other suggestions.

Any ideas