Demand-based fresh air control system

A demand-based air conditioning system (18) for a passenger vehicle that may utilize one or both of a contaminate sensor (34) and a door sensor (16). A controller (36) operates a damper (22) to send an estimated amount of fresh air into a passenger compartment, based on the sensed level of contaminate in the passenger compartment, to ensure the air quality in the passenger compartment is acceptable for passengers.