R134 Conversion Woes - Evaporator Freeze-Up

Something that nobody mentioned is that in 1974 and up Chrysler used an Evaporator Pressure Valve in the back of he compressor suction inlet to shut off the flow of R12 if the suction pressure dropped too low to prevent freezing the Evap coil up. Previously in 1973 back there was an antifreeze switch wired inline with the clutch to shut off the compresser until the temp came up in the evap. In any R134 retrofit you must install a switch to prevent freeze ups and you must remove the R12 calibrated EPR valve for proper system operation. Chrysler went to this setup in 1974 and up to address the complaint of roughness in the engine when the compressor cycled off and on.
The old RV2 compressors were not known for their smoothness but they were a quite rugged design.