direction knob selector

2000 pontiac grand prix se here with 116,000 on it..........the problem is the selector knob on the temperature control unit will not switch the flow of air from defrost setting to the floor setting to anywhere...........it is set in one spot and changing the knob setting does not change the flow.......the fan knob works fine....so does the temperature setting knob...:runaround: any ideas people ???????????????

Have you done any work around the battery/changed batteries? The vacuum supply line for the HVAC mode actuator (the one that switches from floor to vent to defrost) runs near the battery, behind the washer bottle, then to the firewall. It is very common to inadvertently crack this line while working on/near the battery. You can repair it with a small piece of rubber vacuum hose that fits snugly over the existing hard plastic line.