03 Century climate control question

2003 Buick Century with dual climate control. The selector knob that chooses defrost, floor, bi-level seems to move very easily - too easily. I only get a bit of air out of the defrost vents but the system blows strong over all. Closing the dash vents doesn't increase the air flow much. I was thinking at first that it may have a flapper stuck in the system but that selector knob doesn't seem to change anything, like it isn't hooked up. Will pull it apart and have a look. Is it a mechanical vacuum selector or electronic? Hoping I can at least temporarily adjust and get it to blow strong out of the defrost vents instead of the floor and dash. Might have to block the floor vents as well as shut the dash vents to get a temp fix if all else fails. Am I on the right track? Any tips appreciated.

Edit: Air flows from the dash vents at any setting. Air blows slowly from the defrost at any setting.

Pull the knob off.....you will find it broken on the backside.......dealerships have them in stock.....replace them all the time....

The knob looks good. I see that it is electronic switch so it's not hard to turn like on older cars. The dual sliders change the temp fine. But the selector doesn't seem to change anything until it goes to max it kicks on the air conditioner. The vacuum line from the manifold looks good under the hood. I'll take a closer look under the dash and inspect it closer. Friend with a 99 said his system would stick occasionally and flipping the switch about would sometimes free it up. I tried that but no luck yet.