Mode box (air/heat)

I have an 04 cavalier and my switch no matter what setting its on still blows through the vents. Hot or cold air..no defrost or floor. I believe my rear defrost works. And by the way its not digital and the switch if its all the way to right (on defrost) it jumps back same as all the way to the left i can get it to stick but still doesnt work. I talked to chevy and they wanted me to buy the whole box for 228 just seeing if anyone else could help a little.

Seems to be something stuck in the diverter vent/flap assy; or a bad vacuum hose somewhere.
I'd suspect vacuum; unless you lose stuff down the defroster vents often.

Tookie