Heater/Defroster

My 2002 LS 4WD blows air out of the AC vents on the dash, regardless if the switch is set to defroster or to blow towards your feet. There is also a hissing (air leak?) sound from behind the dash.

Locate and repair the "hissing" sound. It is a vacuum leak in the HVAC system starving the blend doors of the vacuum needed to open and close the doors properly.