This GMC truck arrived at the shop with an a/c issue.

The a/c worked, but would not blow from the dash vents.

The photos above and below look into the duct that feeds the center vents in the dash.

The door seen in the photo above moves and directs air to the dash vents.

In this case, the bracket that allows the door to move is broken.

With the door bracket broken, the door is free to move at will and gets stuck in the "floor" position.

With no parts available, my solution was to fabricate a bracket to brace the door permanently in the "vent" position. This means that air will always blow from the vents, which will be fine.