I've owned several F150's and don't remember ever having this problem. It's starting to get cold here, so I've started running the heater. Everytime I have the vent control set to "floor" my front glass fogs up. I have to turn on the defrost. I noticed that when the vent control is in the floor setting- a small amount of warm air is coming out of the defrost vents at the base of the front glass. What would be causing this?
Also, this is a new 2008 F150.

 

Floor =/= Defrost...


It's because when you turn off the defroster, well uhh... you turned off the defroster...

 

My 2006 is the same way, I have to have the defrost on 100% and even then it takes considerable time to clear the windshield. If I use the 50/defrost 50/floor setting on cold foggy mornings I can not keep it clear. My 2000 had a much better heater/defroster.

 

I've noticed the problem starting with my 2004 and continuing to my 2006. My 2001 never had this problem. Now, I just crank the defroster and just use that to heat my SCrew.

 

Trucks with the standard ***** for heating and cooling don't have that setting. I'm pretty sure that's only trucks with the fancy temqerature control screen or whatever.