Ventilation problem

The most common cause is the mode doors are operated by electric motors (actuators) that go bad. Attached below is a guide for blend door actuator replacement.

https://www.2carpros.com/articles/replace-blend-door-motor

Here is a video of actuator replacement on a Silverado:

https://youtu.be/Eqf-H3COtSo

All of the locations and diagrams are attached below.

The mode door control is an electric motor actuator that rarely act like that. You will have to examine the mode actuator during this problem to see if the motor is actually doing that or if there is broken or disconnected linkage there. The mode control will be on the left side of the HVAC housing.

Yes, you are right. The Blend door actuator is on that side but I never said anything about a blend door. I told you to check the mode door actuator. Which is on the left side.

GM has designed in a lot of "got'chas" to cost you money after the sale, and this may be one of them. Volkswagen, BMW, and GM have the most tricks built in that cause these problems after simply disconnecting the battery. Newer vehicles are often worse.

Expect to make a trip to the dealer, but first check the owner's manual, or the service manual if you have one, to see if there is a procedure to reprogram the computer. The only one I am familiar with was on the 1997 and 1998 Caravans and getting half of it to pass could be extremely frustrating. The procedure was initiated by pressing certain pairs of buttons on the control panel.

GM, like almost all manufactures of late model cars, including Chrysler, uses an electric actuator to operate the mode doors and a central module to operate them and either can be bad or one of the air doors can be stuck. It will take someone very familiar with the system and some expensive diagnostic equipment to diagnose it properly.

All good answers but the assumption is this is related to disconnecting the battery. Plus, it works normally for one to three seconds. That should rule out any mechanical problems.

If this happened after disconnecting the battery, this is what happened. Every time the power is cut off the system loses memory and when the power is reconnected the system goes through a calibration process that moves all the doors to their extreme ends for calibration and many of them will get stuck when that happens. It very common on the temp doors. It may unstick itself and you may be able to help it along by pushing on the linkage under the driver's side dash.
There are no vacuum controls on this system.

Thanks Wrenchtech. How long does that calibration process take and how do you it's done and / or passed? If an actuator sticks, then unsticks from bumps in the roads, will it self-calibrate then or do you have to do something to initiate it again?

Sometimes they break free and sometimes they don't. It is initiated whenever the power is interrupted so a battery saver is a good idea if disconnecting the battery for any reason. It happened a couple times to the blend door in my own Blazer. One time it freed up on it's own and another time I had to resort to drilling holes in the housing and popping the door free with a long thin screwdriver but with the mode doors, the gears and detents are on the outside of the case so you can just grab them.

It could be both. You need to check to see if you have a vacuum line disconnected first, but the motor that operates the doors cold be electric. Best thing to do is feel around the heater and see if the door may be stuck. Then you will have to either go through the normal checks to see if it 's the control panel or the switches, etc.

First thing to do is pull the hvac fuse for 30 seconds then see if the heater module will reprogram itself. If not the mode actuator will need to be replaced here is a guide to show you how.

https://www.2carpros.com/articles/replace-blend-door-motor

Please let us know if you need anything else to get the problem fixed.

Cheers