Motor may be too weak to overcome the airflow resistance. You're lucky it works at all.

 

So jaysmachz is definetly right about mode door 1 controlling the defrost and floor vents. I have a 2003 Ram 1500 and I can't seem to get my defrost to work prooerly. I can hear the door close in defrost position and one or two seconds after it flips right back. It's a pretty audible flip flop. So this being said, I blew my cigarette outlet fuse last night and the outlet and my radio went out but I'll be damned if my defrost didn't kick on at the same time. It worked fine for about 30 minutes and then I plugged my dude back it and we're back to square one. Does anyone have any clue what the heck is going on?