More interesting about the 60's GM A/C controls in all but the Chevys is the fact that the A/C controls were on the left of the steering wheel and the heat on the right. I don't remember how the blower figured out which control to comply with. I think the Caddy's with early comforton were the only ones with a single hvac control. The early GM A/C used bypass controls for the freon to control temps instead of the later reheat setup. My uncle gave me his 60 Biscayne with factory A/C (but manual steering!) in the mid 70's. I took it to our local Chevy dealer to have it re-charged. All the young mechanics clustered around it since the A/C system was so "old"!