A damper door controller is provided for remotely controlling damper doors of a cooler/heater unit of an automotive air conditioner. The controller comprises a knob holder; at least one rotary knob rotatably connected to the knob holder; a pinion coaxially connected to the rotary knob to rotate therewith; an elongate guide slot formed in the knob holder; a rack member slidably received in the guide slot, the rack member being operatively meshed with the pinion; a cable assembly including a control cable and a sleeve in which the control cable slides, the control cable having a leading end fixed to a leading end of the rack member; and a clamp member provided by the knob holder and extending across a generally middle portion of the guide slot to clamp a leading end of the sleeve.