Here is a guide that will give all the detail on this issue:
https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position
Your vehicle does not have vacuum control actuators so I am sure you have an issue with either the first or second item in the guide. Either the actuator or the control module. The defrost position is the default position so that if the actuator or anything else fails the system will always have defrost so that your windows stay clear while driving. It can be a safety issue if you windows fog while driving.
Let us know if you have questions and we can go from there. Thanks
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Sunday, May 24th, 2020 AT 5:24 PM