2nd Gen Non-Engine/Transmission Temp in cab is either hot or cold--no inbetween

[Swyers]

When I adjust the in-cab temperature dial in my '99 2500, I either get full heat if the dial is 51% or more on the hot to cold mixture or or full cold air if it is set to 51% or more on the cold to hot mixture.



Engine temp is normal across the board...



Any thoughts?

 

[WestTN]

The position sensor for the blend door is broken.