1972 Duster Build with my Daughter

Jim Kueneman said
FINALLY the Daughters Duster will freeze your nipples off. I will try to limit my rant of aftermarket parts. The POS aftermarket expansion valves flood the evaporator and I went through 3 compressors where the super heat was totallly wrong on the valve and flooded liquid into the compressor failing the reed valves. Bought NOS reed valve plates and a NOS expansion valve (yes it is R12 BUT THAT DOES NOT MATTER). I plan to tighten the spring in the valve on turn in to compensate for the R134A with this valve but all the problems are gone and it is flipping cold 32F on the road on a 75F afternoon.

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Unless the superheat is way off, I would leave the valve alone. They are adjusted from the factory for an appropriate amount of superheat, and the difference in superheat with R-134a will only be a degree or two at most. Not enough to worry about.

For the enlightenment of those who wonder about such things, Jim is correct about the NOS R-12 valve being fine to use on R-134a. If you look at, say, a Sporlan medium temp TXV power head for R-134a, you will see it is marked "R-12 R-134a R-401a". That indicates that it is intended for use with any of those refrigerants. In fact, there are about a dozen refrigerants, most of them interim blends intended to replace R-12 without having to change out the mineral oil, that will work with that power head. As long as the pressure-temperature relationship near 32°F is in the ballpark of R-12, R-134a, and R-401a, that power head will work.