before you begin typing, yes i have searched on this topic! this issue has been beaten many times, i know. heat and a/c only come out of the defrost vent. i have come to the conclusion that its a vacuum problem. every where i read talks about checking the canister behind the bumper. i dont have one, never did. bout the truck a year ago with perfectly working ac and heat from all vents. within the past several months, idk what happened but the heat only came from the floor vents.
recently my buddy was messing with the blower motor and found no vacuum going to the blower motor under the glovebox. idk what he did but now even the floor vents dont work. im not sure what im looking for, never worked on the hvac system.
looking in the engine bay, i see where the 2 hoses for the ac go through the firewall, and i think 2 vacuum lines. one is not connected, but as far as i can remember, it never was.

any help is appreciated, pics especially.

 

best pic i could get of the mysterious hose

 

The vac hose doesn't go to your blower motor. they go to the ac/heater controls and if I'm not mistaken it goes from the switch to the blend door which is what controls where the air comes out.

 

heater control valve maybe

 

Yep.