A/C controls on a 99' Silverado Problem

I need some help. I have a 99' Siverado and the controls that changes the air from the feet to defrost doesn't work. The knob turn yet it stays on the Defroster. I've checked all the fuses and they seem to be good. The fan switch works and the temp switch works okay. Just can't get it off the defroster mode. Does anyone have any suggestions?

Thanks

Ruger9mm

More than likely it's going to be the control head. Dealer item about 135 bucks not including labor. But if you can do it yourself, it's only about a 10 minute job.