Inlet Air Control

Inlet air control
The inlet air source is automatically controlled while the system is off or on. While the system is on, the inlet air source can also be manually controlled to give timed recirculated air or latched recirculated air.

While the system is off, the ATC ECU uses vehicle speed to determine the inlet air source. With the vehicle at rest, the inlet air source is set to recirculated air. When vehicle speed reaches 17.5 mph (28 km/h), the inlet air source changes to fresh air. The inlet air source then remains at fresh air until the vehicle speed decreases to 5 mph (8 km/h), when it returns to recirculated air.

While the system is on, the ATC ECU uses the LH and RH temperature selections, vehicle speed, ambient air temperature and coolant temperature to determine the inlet air source. In the automatic mode:
^ If one temperature selection is set to LO and one is set to a specific temperature or HI, the inlet air is set to recirculated air.
^ If one temperature selection is set to HI and one is set to a specific temperature or HI, the inlet air is set to fresh air.
^ When specific LH and RH temperature selections are set, the inlet air source remains at fresh air except when the air distribution function is set to face level only or face level and footwell outlets. If the air distribution function is set to face level only or face level and footwell outlets, at 56 mph (90 km/h) the inlet air source changes to recirculated air (to exclude ram effect, which becomes excessive at speed). When the vehicle speed decreases to 37.5 mph (60 km/h), the inlet air source returns to fresh air.

In the defrost mode, the inlet air source is set to fresh air except at low ambient air and coolant temperatures. If, within 5 minutes of the ignition being switched on, the vehicle speed is less than 5 mph (8 km/h) while the external air temperature is -16 degrees C (3 degrees F) or less and the heater coolant temperature is -10 degrees C (14 degrees F) or less, then the inlet air source is automatically set to the timed recirculated air mode. The timed recirculated air mode is cancelled immediately the vehicle speed reaches 8 km/h or more.