Blower Control
IHKA equipped vehicles have a blower final output stage in place of the resistor pack. The output stage is installed in the blower assembly.
In AUTO mode, the blower is automatically regulated. In the manual mode, 8 blower speeds are available. These correspond to approximately 20, 30, 40, 50, 60, 75, 90 and 100% of battery voltage.
The blower relay is energized by the BC1 whenever the ignition switch is in position 1 or 2, and the IHKA module modulates the output stage to regulate the voltage across the blower motor to control blower speed.
In the automatic blower and fresh air mode, the blower speed is corrected for vehicle speed to compensate for the increase in ram effect on the inlet air as the vehicle speed increases.
In the automatic mode, if the temperature is set to LO or HI, the blower runs at maximum speed with correction only for vehicle speed. When the temperature is set to a specific temperature, blower speed corrections are added to compensate for the heater coolant temperature, external air temperature, and the solar load on the vehicle:
- During warm-up, to avoid blowing excessive amounts of cold air into the passenger compartment, the blower speed is limited if the heater core air temperature is below approximately 60°C (140°F). A similar limitation is applied when the exterior temperature falls below -10°C (50°F).
- During cool down, to purge the ducting of hot air, blower speed is limited for a period of approximately 5 seconds after the system is switched on. The blower speed is then progressively increased over a period of approximately 10 seconds.
- As the temperature in the passenger compartment approaches the selected temperature, blower speed is progressively reduced until, once the selected temperature has been established, blower speed stabilizes.
- Solar heating correction is employed and progressively increases the blower speed with increasing values of solar heating.