Airflow

Operation
Blower motor voltage depends on the position of the airflow selector wheel and of the control unit lever, and can be seen on the airflow graph. The blower is continuously varied in speed by 2 electronic power output stages.

This principle comes into effect only when coolant temperature has reached at least 60°C (140°F) (see also cold-start inhibiting circuit).





The airflow selector wheel has the following settings:
Between 0 and 4 % of the adjustment range of the airflow selector wheel, the entire air conditioning and heating system is shut down and blower motor voltage is then 0V.

Between 5 and 34 % the blower motor voltage remains constant at 4.5V. In this range, the airflow can be additionally influenced in three stages by opening the two fresh air flaps.

[] 20 % of full airflow
[] [] 50 % of full airflow
[] [] [] Full airflow (100 %)

Above 35 % blower motor voltage is influenced additionally by the position of the control unit lever. The blower motor voltage graph is trough-shaped, so that the voltage now rises steadily as the airflow selector wheel is advanced further. At 94 % airflow volume, the maximum voltage of 11V is reached.

If the airflow selector wheel is moved to the 95- 100 % setting, the blower relay connects it to the car's electric power supply directly. This eliminates a voltage drop of approximately 1.5V caused by the control unit.

The blower stages of the regulating electronic circuit are located in the blower half-shells. They are provided with an electronic overload cutout, which also protects the blower motor.

Airflow Graph:

1 = Airflow selector wheel setting in %
2 = Through flow of air in %
3 = Blower voltage in V
4 = Position of control unit lever in %