Quote:
Originally Posted by gsxr
UPDATE: The winter temperature control problem has been fixed with the new duovalve. I'd be ecstatic if there wasn't a new problem, described here... I now have proper temperature regulation, but there is a vacuum issue which prevents airflow to the footwell area in sub-freezing temps.

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If you're speaking of the W210, I had that issue very early in my ownership of the car. It ended up simply being the control rod popped off the flap just inside the foot well heater exit.
I just took the grill off it and reached in with a finger and popped it back into place. Toasty feet!