Air conditioning (Auto operation): Description and operation (page 2 of 2)

When the ignition is switched on, the system will start by measuring the various temperatures and light. If the outside and inside temperatures are low the calculated required air-off temperature will be high. The unit will select maximum heating with blend flap fully open, distribution flap to feet and maximum heating airflow. However, because the engine coolant temperature is low the blower and distribution selections are overriden by a WARM-UP CONTROL.

If the set of conditions selected by the system calculations were allowed at this point, a large volume of cold air would be forced through the car interior. The system overrides to warm-up control until an engine coolant temperature greater than 30 °C, 86 °F is reached. During this phase, all the air is directed to SCREEN and the blower operates at LOW speed. As the engine coolant temperature reaches 50 °C, 122 °F the blower is running at FAST speed for maximum heating. At this point, the distribution flap moves to FOOT level with a small bleed to screen.

The blower will continue to run at FAST speed until the interior temperature is well above zero. Then, as the interior temperature approaches the setpoint the blower speed will start to reduce and the air-off temperature from the heater will fall.