Ford Repair: F150 Heat and air control problem, electrical actuators, model trucks

Question
The A/C works well and the blower is working fine. but when i accelerate I hear a thump and the air blows worm I can get the air to blow cold if i mass with the controls I would like to try to fix it myself, but I don't know how the system works so i don't know where to start.  Thanks Paul  Vicksburg MI.

Answer
first i need year make and model as early models are only vacuum controlled-later models are controlled by vacuum and or electrical actuators-if your vacuum supply is steady from outside to inside you could have a bad vacuum motor but later model trucks are breaking blend doors and the whole dash may have to come out a 6-7 hour job if you have done several.

later models are 97 up.