2009 lacrosse air flow

The heater in my otherwise perfect 2007 LaCrosse has developed a strange malfunction. When the temp knob is all the way to the left (as for max A/C), the air flow is strong. However, the further to the right the knob is turned (into the red), the weaker the air flow becomes until nothing comes...

I'm not getting hot air on the floor or defroster settings. Last winter was a pretty frigid drive to work. In the vent-only mode the air temp is 115 f. (kitchen thermometer). Outdoor temp today 75f. Vent-floor mode does get a little heat to the floor, floor-defrost and defrost does not get...