Straight propane has pressures that are WAY too high for MVAC use. The P/T curve for propane is almost exactly that of R22, not R12. It's use in Mexico would add more excitement to an already exciting driving experience there
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The addition of ~30-40% isobutane to propane puts the thermodynamics more in the R12 range.
I AM NOT ADVOCATING THIS. I have used a "test" refrigerant when I had a particularly difficult leak to find (it was leaking thru the WIRES of the aux fan switch as it turned out!!) and found it performed nicely; very much like R12; not better, but like R12 IMHO.
Your symptoms (would REALLY help to have pressures, ambient, RPM, but.....) are classic for lack of heat exchange at the CONDENSOR. I know you say the fans are perfect, but the rain scenario says otherwise. Low charge will do the same.
Why are you replacing those parts on an operating system? Leak? compressor noise?