The Air Vac is a vacuum system which allowed KITT to suck out smoke (mostly from a small bomb) from the car's interior.
I swear, Michael. No more bean burritos for you!
("Knight of the Chameleon")
KARR contemplated using his Air Vac to suck the air out of the passenger compartment as a way of killing his captive. Instead, he chose to raise the temperature ("KITT vs. KARR)