I am looking to add A/C to my '69 roadster. Does anyone know the difference between the VIR equipped cars ('73 to '77) and the P.O.A. valve cars that preceeded them? It would appear to this A/C illiterate that the VIR is a combination of the dryer, receiver, and expansion valve. Is it better to allow for compressor cycling with the Sanden 508 compressors?