HVAC controls
 

Hi, I am having problems with my HVAC air control. It is only blowing out to the floor. I can not change to vents, defrost or anywhere. I am told that I need to replace the actuator. My truck is 2005 Silverado, 4wd, 5.3 liter, extended cab, short bed and has manual dual controls for HVAC. Temp is fine, just cannot move the air around. How can I be sure that it is the actuator and not the control knob itself?