I just fixed this issue and found a possible fix. When you select a diffrent mode a motor turns more or less a wheel that has arms in specific tracks that open and close vents when it rotates to the desired position. One of the arms on my van came out of its track and Jamed it. I had to remove the panel under the steering wheel, and honestly just used a butter knife to pry the arm back slightly and turned the knob and the wheel rotated until it was above it’s track and I pushed it back in. The arm at the bottom is the one that jumped it’s track and jammed.