I was wondering if anyone knew anything about a problem or a similar issue that I have been experiencing regarding my 1982 633. It has the older-style controls (the three knobs in between two airflow selector control arms shown below) and the knob to the far right controls the direction of air flow, either none (3 o'clock position), heat (6 o'clock position), normal (9 o'clock position), or front defog/defrost (12 o'clock position). An unusual problem has started where the selector knob no longer goes past the normal position and I cannot choose the defog setting. The resistance that you feel is not a sudden stop, but rather you can rotate the knob to the position, but then it will spring back, with almost an elastic tension, to the normal position; if you hold it in the defog position it does not work either. Has anybody had this problem before or know what it might be?