manual temp dial won't turn fully
 

The other day in my 99 9-3, I was turning the dial for less heat, and the knob broke off. Today I tried to turn the stem using pliers, and instead of the dial moving from 7 o'clock to 5 o'clock, it only moves from 12 to 5. Basically the heat is permanently on.

Can anyone recommend what part needs replacing? Could it be just the stem is stuck on something? Is there a spring in there - or do I need to replace the entire unit?

thanks.