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:
l 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.
l 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.
l 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 °C (3 °F) or less and the heater coolant temperature is −10 °C (14 °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 .
Timed recirculated air
The timed recirculated air mode sets the inlet air source to recirculated air for 5 ± 1 minutes, after which it automatically
reverts to fresh air. Timed recirculated air can be manually selected:
l In the automatic mode, by pressing the fresh/recirculated air switch for 1.5 seconds or more; the audible warning
sounds twice.
l In the economy or defrost modes, by pressing the fresh/recirculated air switch for less than 1.5 seconds; the
audible warning sounds once.
Latched recirculated air
The inlet air source can be latched to recirculated air:
l In the automatic mode, by pressing the fresh/recirculated air switch for less than 1.5 seconds; the audible
warning sounds once.
l In the economy or defrost modes, by pressing the fresh/recirculated air switch for 1.5 seconds or more; the
audible warning sounds twice.