2003 sierra My ac vents stay on defrost on my 2003 GMC Sierra 2500hd 6.0L

[ElJohnnyBoy]

I switched out the blend door actuator under the drivers side (it controls the different modes/vents). The old blend door actuator was making a clicking noise, so I decided to install a new part and when I did clicking noise was gone, but now I couldn’t switch to different vents/modes. When I first started it up the actuator went through all the different vents/mode, but then when it got to defrost it just stayed there. I thought the actuator was bad, so I got another one, but the same thing happened again. What could be the problem?

Edited April 13, 2021 by ElJohnnyBoy

[davester]

It's possible the post on the door itself is damaged/broken.  Maybe try using your phone to take a picture of the area, or an inspection camera, and see how it looks.