heating adjustment dial stuck on ford mondeo 1996?

the dial for adjusting the heat temperature in my ford mondeo is not working it seems to be stuck in one position and if you try to move it , it springs back to the original position.
my daughter has been playing in the car on a recent camping trip and i think something has maybe been stuck down a vent.
ive tried moving the dial back and forth in a bid to dislodge whatever it is. i `am wondering if i need to take the dashboard off to reach the heating system???????

lee johnson
September 2007