my fan and venting is stuck
 

i bought my car used and have done some minor work to it, its a 95 rodeo, and i have one problem that i was hoping to get some feedback on before i start ripping the dash apart.

the vent lever, doesn't seem to change the flow of air... 90% of my air comes out at my feet, but my defroster vents put out very little air... which is incredibly annoying, does anyone have a diagram or photos of how the vent's and their air flow louvers are set up? or any advice on how i could improve airflow to my defroster vents.