The vertical heat levers are attached to square rods behind the unit. By lifting or lowering the lever it turns the rod. There is not a lot of play in it so that may be why you either get hot or cold without much in-between. It is a bear to get to but it can be reached by removing the cardboard shield below the glove box and working on your head. Taking the front unit (where the levers and climate controls are located) off does not gain much of an advantage and there is a chance of breaking some of that old plastic facing. This info. is from my 74 450sl.