Any AC Techs

The clutch cycling switch in the '65-'72 factory heat/AC system is controlled by the temperature slider lever (which also operates one of the air doors on the heater box). Find what moves on/near the box when you operate the temp slider back and forth. The clutch cycling switch has a small-diameter copper sensor tube buried between two fins of the evaporator, so that's another way you can find it. But it sounds like yours might be missing.