there are a series of vacuum lines behind the dash that allocate where the air is to be bown upon your selection with the heater/ac ****. There are 3 vacuum bases I believe. If you hear ANY hissing behind the dash selector **** you have a leak there, and can use clear silicone to tighten the seal. If there is no hissing there listen around under the middle and right side of the dash for other "hissing/Leaking" sounds. Here is a pic of the unit under the dash
Last edited by MONSTERPRE; 12-28-2010 at 05:48 PM.
Reason: 3 vacuum bases. far left is for defrost, middle is for floor/vents, under the hood is for heat/econ