If the 67 you have is anything like the 62's then the switch runs a cable to the heater box which opens and closes a flapper. I would grab a flashlight and look under your dash while operating the controller or heater switch and see where and to what the cables run to. You may find one is missing or simply off. Let us know what you find; again the 67 may be a totally different operation than the 62 models.

What kind of car is this on?