for those of you that have done the hvac mods, or fixed your systems, i have a question. my truck just started to not let me direct air to the bottom, at my feet. i can change the vents to top and then back to floor, and it will move the air there, but after a few seconds it will re direct it back to all the vents. was wondering which problem i have?
i also did a search on this, and found some of you have done a write up or know where i can get that write up??? i couldn't find it..
i'm not sure if its a actuator problem, or if a mode door is broken??? nothing rattles or makes noise.

 

My guess would be the heat/floor door or coupler is broken, so that the door does not open when commanded. In that case, air pressure in the case (fan blowing with no doors open) might push past the vent door?

Anyway, here's where a guy did a nice write up. It also links to a write up on dash removal.

https://www.dieseltruckresource.com/....html?t=210483