[jayoldschool]

There is a vacuum line disconnected. The "blend door" regulates the hot/cold air by opening and closing the air that goes past the heater core. It is controlled by a diaphragm that is operated by a vacuum line. Get your head under your dash, and take out your glovebox liner (the black felty part) and start looking for vacuum lines disconnected. Check up on the intake manifold, too.