System Operation
The solar sensor receives power (5 volts) and ground from the IHKA control module. The
module then reads the voltage drop across the photoresistor and determines the degree of
solar heating based on the change in voltage. The voltage drop across the photoresistor
increases as solar radiation increases. The IHKA control module monitoring voltage will
decrease indicating an increase in solar heating. The module processes the input every 10
seconds and checks it for plausibility based on a limit value monitoring function.
Values outside the limit indicate a malfunction and the signal from the sensor is ignored by
the module.
As solar radiation levels increase, the control curves, stored in the IHKA module, for the
blower fan, mixing flaps and ventilation (face vent) flaps are shifted to compensate for the
additional heat.
The solar sensor inputs to the IHKA control module can influence the settings on the rele-
vant side (driver/front passenger) on the E38 and E39. No separate regulation is possible
on the E46.
When driving at night, during cloudy periods or through tunnels, the control maps are shift-
ed back to their base settings.
20
E46 Climate Control
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