Well, no. Auto AC is pretty easy, actually. ALWAYS flush the system, ALWAYS replace the Accumulator/Receiver Dryer to dispose of accumulated contaminants and oil, always drain the compressor of oil and then install the recommended amount of the correct oil for the type of refrigerant being used. You CAN retrofit a 1967 Chevelle with the original radial compressor to R134A and have it blow ice cubes, just as cold as an R12 system. I've done it.
The big issue with R134A is not that it's an "inferior" refrigerant; it's actually a better refrigerant. It runs cleaner, the synthetic oil used with it means compressors (as long as they remain uncontaminated) run twice as long, and they run cooler as well.
You just have to engineer the AC system correctly. R134A has a higher latent temperature; it also has a greater expansion coefficient when it changes state. This means that to work correctly, it has to operate in a high volume mode, where R12 works best in a high pressure differential mode. R12 systems use a series core or "serpentine" condenser; all the refrigerant travels back & forth across the airflow surface. The Evaporator is also usually serpentine core; though some later R12 vehicles were parallel-core; meaning the refrigerant is collected in a manifold at one end, which distributes it so it flows through all the cores simultaneously as it changes state to a gas again.
A proper R134A system has condenser and evaporator that are both parallel core. This is also why native R134A systems tend to have larger diameter tubing; they work on volume, not pressure.
Simple, really. Until they come along with variable displacement compressors; now THAT's all a whole 'nuther ball of wax...
mnem
*Under pressure*