Abstract: An automotive HVAC system controls two side by side film belts with a single drive motor. Two co planar wind up rollers, one for each belt, have inboard ends that are indirectly connected by a rotation transmission means that has a defined level of turning “slack”. Rotation is transmitted from one wind up roller to the other only after the slack has been taken up, allowing a certain degree of offset between the two belts. When a first belt is turned past a first position, it eventually moves the other belt to a new position, with the defined belt offset maintained. The first belt can then be turned back, breaking the indirect connection between the two shafts.