Maybe dealer or aftermarket a/c who knows? There are no obvious signs of it The heater controls are standard there are no extra holes under the dash , no odd ball vents or other hoses. But it is a 53 year old car that isn't completely stock or unmodified. When I bought it there were wires through the double hole with a big gob of black dumb dumb sealing it.
The heater controls would have been left alone and the control for the AC would have been on the under dash unit. The system was removed before you got it. In the 70s and 80s it was common to delete AC systems as they steal HP or so people thought.
