Auxiliary Fan Control

IHKA E38 [1][2]AUXILIARY FAN CONTROL (up to 96 MY)
The auxiliary fan on E38 vehicles is a two-speed unit, and it operates similar to the auxiliary fan on previous IHKA systems.







- The IHKA control panel/module energizes the normal speed relay to run the fan when the A/C compressor is operating and ambient temperature is 50°F (10°C) or higher.

- When refrigerant high-side pressure exceeds 290 psi (20 bar), the pressure switch contacts close, energizing the high speed relay. The fan runs at high speed.

- When coolant temperature reaches 196°F (91°C), the coolant temperature switch normal speed contacts close. The fan runs at normal speed.

- If coolant temperature continues to rise and reaches 210°F (99°C), the coolant temperature switch high speed contacts close. The fan runs at high speed.

[1][2]Auxiliary Fan Control







The [1][2]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 fan 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.

[1][2]AUXILIARY FAN CONTROL ('99 MODEL YEAR - E38)







The [1][2]Auxiliary Fan motor incorporates an output final stage that activates the fan motor at variable speeds.

The [1][2]auxiliary fan is controlled by ME 7.2 (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 cluster 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.