Auxiliary Fan

AUXILIARY FAN







The auxiliary fan is a three stage operation as introduced on the 1996 E38.

Stage 1: Activated simultaneously with the compressor with an ambient air temperature > 10°C (50°F). If the coolant temperature rises to > 91°C the tan will also be switched on. Fan Speed = 1250 RPM.

Stage 2: Activated when the medium pressure switch on the receiver/dryer closes at 17.5 bar. Fan Speed = 2000 RPM.

Stage 3: Activated when the coolant temperature reaches 104°C at the double temperature switch. The stage 3 switched voltage circuit is protected by a 50 amp remote fuse (red). The fuse is located in the electrical carrier forward of the glove box.

AUXILIARY FAN CONTROL ('99 MODEL YEAR - E39)







The Auxiliary Fan motor incorporates and output final stage that activates the tan motor at variable speeds.

The auxiliary fan is controlled by ECM. The motor output stage receives power and ground and activates the motor based on a PWM signal (10-100 Hz) received from the ME 7.2.

The fan is activated based on the following factors:

- Radiator outlet temperature sensor input exceeds a preset temperature.
- IHKA signalling via the K and CAN bus based on calculated refrigerant pressures.
- Vehicle speed
- Battery voltage level







When the over temperature light in the instrument dust is on (120°C) the fan is run in the overrun function. This signal is provided to the ECM via the CAN bus. When this occurs the fan is run at a frequency of 10 Hz.