Maybe it is still going but not getting through to you?
I am sort of looking at the possibility of low vacuum to the HVAC controls, sort of "defaulting" the door(s) to another position.
A few possibilities might be:
Engine wear/need of a tune up/possible vacuum lines broken or cracked or not attached. If there is a vacuum reservoir, maybe it is not hooked up.
A vacuum gauge hooked to the intake and ran back into the cockpit might show what the actual vacuum is when this is happening.
I have a "shop gauge" for tuning and one mounted on each of my Jeep dashes. Vacuum gauges are great diagnostic tools for an engine before tearing into one!
Here is a guide for vacuum leaks:
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
Keep us posted, if you need more information let us know.
The Medic
Images (Click to make bigger)
Tuesday, May 29th, 2018 AT 3:35 PM