Air stuck on defrosters

[Synna]

I have a 99 park ave. Supercharger ultra and it’s been stuck on the top air vents since I got it. I’ve tried searching the problem and only finding things for the LeSabre. Is there a way to fix it?

 

[HotZ28]

Typical blend door failure!

 

[02LTD2.0]

I had a 1998 Olds 88 that would always blow through the defroster vents. I had a vacuum leak right before the vacuum line goes through the firewall to the HVAC unit. A one and a half inch piece of vacuum hose solved the problem.

 

[HotZ28]

I don't remember if the '99 was vacuum controlled actuators, or electrical servo controlled. Maybe someone here can help clarify.