Air Flow Control

When the air conditioning system is in the automatic control mode, the air flow is determined based on the TAO calculated by the ECM. The blower fan speed is controlled accordingly.

In the automatic control mode, the minimum air flow is different between DEF mode and the other modes. For the minimum air flow in BI-LEVEL, HEAT and DEF/HEAT modes, a voltage of 5.5 V is applied to the blower motor, while for the DEF mode a voltage of 9.0 V is applied.

The minimum air flow is corrected by the sunbeam intensity if the VENT or BI-LEVEL mode is selected.

Fig 1: Graphical Representation - Air Flow Control

Courtesy of SUBARU OF AMERICA, INC.

When the blower motor is turned ON in the automatic control mode, the fan speed is initially low and then gradually increases (applied voltage increases by 1 volt every second until an appropriate voltage is reached) to prevent air from blowing out in a gust.)

Even when the blower motor is automatically turned ON, the blower fan is kept stopped or allowed to rotate at the minimum speed for a maximum of 150 seconds depending on the cabin temperature and the ambient temperature, if the engine coolant temperature is below 49°C (120.2°F) with the air outlets for the VENT or DEF mode selected.

After the conditions for prohibiting blower fan operation or limiting its speed are removed, the voltage applied to the blower motor is increased gradually (by 0.34 V every minute) such that a large amount of cold air does not blow out toward the leg area.

Once the coolant temperature exceeds 49°C (120.2°F), the normal blower fan control is performed including the starting speed control.

The blower fan is stopped for 3 seconds if the compressor is turned ON with the intake sensor-detected temperature is higher than 35°C (95°F).