2012 peterbilt 388

Go in through the 2 main dash panels and follow the y ducting for defrost down to a big chamber. There is a drum inside that rotates to direct air. Actuator is on the left of it. Pull the actuator and grip the drum stub with you fingers and see if it moves. If it moves you need an actuator, if it doesnt there is some spitz or a pen caught in the drum. You can try blowing air down the defrost as you wiggle the drum to dislodge it.

 

Pull the actuator off and rotate the drum by hand back and forth. Whatever is lodged needs to come out the top by hand or may fall out the bottom and gone to neverland.

Once the debris is gone, put actuator back on and check op for full travel.