air conditioner / heater / defroster

I have a 1998 chevy silverado that has some problems with the air conditioner / heater / defroster.
The fan works just fine & so does the air conditioner & heater, but the air only comes out at the floor.
When I adjust the knob though all the availabe positions including defrost, the air still only comes out at the floor.
Any help or suggestions would be extremely appreciated.

sounds like maybe the motor that opens and closes the door that changes the direction of air flow has stopped working for some reason maybe an open circuit or ground. or maybe the swith could be bad. just possibilitys.. good luck and let us know what you find is the problem.
Chris

any other ideas ?

Have you tried removing the knob to see what position the switch is in? You may have worn or broken the i.d. of the knob and not actually be turning the switch.

not sure if 98 is the same as 93s but mine was doing the same thing the linkage that opens the vents had fallen off take ash tray out and look up at side of heater box should see linkages move thru positions and see if controls move should be able to determine if its the motor or just the linkage I had to put some epoxy on mine to keep it on.
hope this helps.

some climate controls work with a vacuum instead of a wire or motor, maybe it´s a leak

It also could be an electrical connection to the switch. Seems to me on the my 99 when you change where the air is to go, no mechanical sound is heard.
Maybe change you directional switch and see if that helps.