The air conditioning system is designed to allow up to approximately 10 percent of the air coming from the air vents to be fresh air from the outside. The exact amount of fresh air entering the vehicle on recirculation mode will vary. If the A/C system is turned on in the AUTO mode, then the A/C ECU switches the air intake ducting between "fresh," "fresh and recirculation mix" or "recirculation" according to the required outlet air temperature that the ECU calculates. This calculation is based on the temperature that is dialed in with the control knob, the interior air temperature and the operating conditions.