Auto Air Conditioning & Heater Repair: Pontiac ac blows from defrost vents only, plastic tank, fire wall

Question
When I run the ac, the air only comes out of the defrost vents on top of the dash and not the front vents no matter if we switch to the front or floor setting. Why is this? 1999 Bonneville with Electronic claimate control


Answer
Hi Will

The system works with vacuum from the engine.  Check at the fire wall on drivers side you will see a black plastic tank.  This should have two hoses connected to it.  Make sure the thick one has vacuum coming the engine area and the thin one is connected to the tank.  Let me know if you need anything else.