So, I have not yet mapped out the entire circuit yet. The information I have gathered to date points towards this unit as being a simple linear voltage regulator controlled by the zero to six plus volts DC coming into the unit and providing a low to 12 volts DC to the fan motor. This is inefficient and wasteful (Heat).
It has been suggested that this module has some sort of function relating to temperature control of the system. IT DOES NOT!
The HVAC Fan is only low to high with five stages of speed adjustment. The ambient temperature and the temperature of the air moving through the system tells the HVAC system how much heat or cooling the air requires to achieve the desired temperature setting of the occupants.
From the Crossfire Specialist Student Reference Book:
Heater Mode
The heater core temperature sensor measures air temperature at the heater core while the ambient air temperature sensor determines current outside temperature. The system electronics compare the various measured values with the requested temperature. The electronics adjust the coolant flow to the heater core to add or remove heat, as required.
Cooling Mode
An evaporator temperature sensor measures the temperature on the evaporator air outlet, while an ambient air temperature sensor determines current outside temperature. The system electronics compare the desired temperature set on temperature dials with ambient temperature, and control blower temperature by programming stored in the control and operating unit. Electronics adjust the air conditioning or hold current settings constant as required.
From this we can deduce that the control is to the temperature of the air itself ultimately, NOT the fan speed. So the fan speed is occupant controlled only.
That being said, I am looking into a cheaper PWM control system that can simply replace this POS. BMW, Mercedes and of course Crossfires all suffer from these regulator modules dying. Funny that both BMW and Mercedes use the same ELMOS IC in their units.