1999 Chevy Suburban HVAC Mode Selector Switch

The mode selector does not work. In other words when selecting defrost, or other modes it doesn't change to the correct position. It just continues to blow from the same place.
Blower seems to be working fine, and in fact I replaced the entire dash control panel thinking this was the probelm, but it is not.
Is it a relay issue or perhaps something else?

Thank you