Need a new heater core, presumably.

[ChickNorris]

Simple check. If the cruise control works it's your blend door. If the cruise doesn't work it's a vacuum leak

Can't remember using cruise control in the last five years. Nope, doesn't work. Idiot light in the console does however. Heh, forgot what a lovely shade of green it is.

Thank you very much. That was a nifty trick.