Yep, this happens when the small vacuum line going into the firewall from under the hood is broken or disconnected from the engine, I would raise the hood to inspect this small plastic hose. please go over this guide to see what I am talking about:
https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position
Check out the images (below). Please upload pictures or videos in your response to any problems so we can see what to help you with. Here are the vacuum lines under the dash which can sometimes be broken as well.
Images (Click to make bigger)
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Tuesday, June 11th, 2024 AT 11:20 AM