ok, so this morning was the first time I've had to use my defrost since getting the car. I found out that no matter what buttons I push on my HVAC, the air only blows out of the vents and a little on my legs. the rear defrost seems to work just fine, but the front ducts don't change.

there's a slight hissing noise coming from around the HVAC controls that gets louder if I push in just the heat/feet button.

any ideas? is the HVAC run with vacuum? something just isn't changing correctly...

J.

 

yup the vent controls run on vacuum. there's a vacuum line from the intake manifold that has a 1-way valve and goes through the middle of the firewall somewhere, the vent controls vary with year and model car and version of ventilation you have (ECC vs MCC on the 700/900s, etc).