I tried but could only buy the get the 134a rotary compressor and reasoned that if I wanted to upgrade the compressor in future the increased Max pressure rating would be still good for 134a refrigerant upgrade .
Also just trying to get out of pulling the expansion valve ! Also have a bottle of R12a that I would like to reuse for the recharge .
I would have thought the refrigerant type itself , volume of refrigerant in the system combined with the expansion valve orifice effectively sets the maximum circulation pressure of the system and if the compressor is rated for a higher maximum pressure all well and good. The system should stabilize at the pressure drop set by the TX valve and the refrigerant vapor pressure and fill . If the compressor was pushing more R 12 a refrigerant around it would just be a bit colder in the cab .
It appears the seals and lubricant in the compressor would still be compatible with the R12a as this is less aggressive than the R134a.
If not sounds like the dash may have to come out again ....
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