The cooling fan unit

Cooling fan unit speed calculation

The engine ECU sets the cooling fan speed setpoint according to the following parameters:

• engine coolant temperature measured by the sensor, and pre-programmed tables in the engine ECU,
• cooling requirement associated with air conditioning, managed by the internal B.R.A.C. function.

GMV speed control

The GMV has 3 operating speeds.

The engine ECU controls low speed and high speed.

The BSI controls medium speed, based on information supplied by the engine ECU via the CAN network (engine coolant temperature and refrigerant circuit pressure).

GMV speed control

+ APC: + After ignition on

+ BAT: + Battery

Low speed is obtained by supplying the cooling fan unit through a resistor connected in series in the supply circuit.

Medium speed is obtained by supplying the cooling fan unit through two resistors connected in parallel in the supply circuit.

High speed is obtained by supplying the cooling fan unit directly.

The 2 resistors are located on the front panel, near the air-to-air heat exchanger and the cooling fan unit.

Post-run ventilation

Ventilation must continue when the +APC supply is switched off with the engine running if the engine coolant temperature measured by the sensor is above a programmed threshold. The cooling fan unit is then required to run at low speed for a maximum of 6 minutes.

!!! Note: The cooling fan unit must not be activated during:

• the entire duration of power-latch operation,
• shutdown of the Engine Control Module electronics,
• the engine starting phase.

Degraded mode

A fault in the Cooling Fan Unit (or a fault in the low-speed and high-speed controls) causes it to run at high speed.