2006 UZJ100 HVAC gets stuck in hot or cold until restart

[glorm]

Been chasing a problem with the HVAC, that based upon searches here and elsewhere, is caused by the air mix servo system. What happens is it will get stuck in full cold position or full hot position and will stay there until I turn off the ignition and then restart. I can see the arm circled in the pic move to the what I think is the other end of its travel (hot vs cold might be reversed, I can't remember lol), and air does change to hot (or cold).

Now if I move temp back to cold, the air stays hot and the arm doesn't move. However, when I turn off and restart, I can see the one part of the mechanism circled move smoothly to the other position and air is back to blowing cold.

So, because the arm does move and the air is hot and cold as expected, I'm thinking there's actually nothing wrong with the servo motor but instead something confused in the electronics that gets reset when powering up. This actually makes me feel better because I wasn't looking forward to trying to replace the servo motor based on how awkwardly it's located.

Thoughts on how to proceed with troubleshooting/repair? Also, should that nipple actually be riding in a groove somewhere? Since it works I'm thinking not, but can't find a good pic in the service manual or here that shows it.

And yes, I checked the tube & sensor near the drivers seat. No, I haven't checked codes - will do that this pm.

 

[leveeguy]

I think the rod located where I put the yellow marks (right behind the piece you circled) at is responsible for moving the blend door. Check that rod make sure that rod is properly engaged into the plastic arm it moves and is not free spinning without moving the arm. Hard to tell but that rod may be slightly lower than it should be or the plastic piece is a little to high.

Correction: The plastic arm connected to the metal rod I highlighted, moves the rod connected to the blend door, not the rod moving the plastic arm as I first mentioned. The piece you circled is correct and not connected to anything but it moves along with the other parts when temp adjustments are made

 

[glorm]

I was thinking along those lines, but the fact that it actually works right now except for getting stuck, made me think otherwise.