Guys,
I don't know if this will help or if it will work on your car but -- on my 05 GT, if I turn the system from defrost to off -- then wait about 5-10 seconds -- then turn it to floor, I get a good flow of air out of the floor ducts and almost none from the defroster. I learned this by accident, but it works everytime on mine. Perhaps it will be true for at least some of ya'll as well.
M-73

 

Ding ding ding! Almost all systems bleed a little air to the window even on the 'full' floor setting for that exact reason.

 

It's not a 'little air' - it's like 60% of the air goes to the dash and makes your face all nice a toasty. I want my feet warm not my face.

On a side note, I rented a Mazda6 (which I think is built at the same plant as the Mustang) and it does the same thing - too much heat coming out of the defroster and into your face.

 

I'm now a member of this club too. Something happened to my ventilation system. I did not have this problem up until this past Monday. Car built 3/30 had it since 4/15. I used to hear the air flow and feel the air on the floor when set to FLOOR but now when I set to FLOOR I hear a loud volume of air going to the defroster and little to the floor. I didn't do anything different, just set the selector as usual and it just happened. I'm thinking a break down in the gate system not closing off the path as it should. :scratch:

 

hey- found a workaround for warm feet tonight

put control to the left, use the floor/dash vent setting and close dash vents- if fan set at '3' or less it wont whistle, and you get warm feet...aaaahhhhh

only problem- 5 minutes later windshield foggs up(tells me the bypass is a control issue- NOT a door issue...it shuts defroster vents off completely).

if I ever get into the dash I'll try to figure out plenum controls...theres got to be a way to fix this.

 

Its obvious that it is not supposed to do this because sometimes all airflow comes through the floor, and sometimes 30% floor and 70% defrost. Does Ford think we're stupid?