Engine Cooling Fan Control
Engine cooling fan control
The engine cooling fan (FC) is switched in as normal by closure of the thermostat in the radiator.
However, the FC can also be started by means of the ECC control module, in which case it is controlled by the vehicle speed, by the ambient temperature and by whether the compressor is running.
When A/C is engaged, the FC is also controlled by two pressure switches, one for low speed and the other for high speed.
On and off operation is subject to hysteresis (the overlap between switch-on and switch-off). (Compare the case of an automatic transmission shifting up at 70 km/h/44 mph and down at 65 km/h/40 mph.) Conditions a, b and c below must be met for switch-on.
a. Ambient temperature >= 28 °C (82 °F): Switch-on if b and c are also fulfilled
(Ambient temperature <= 24 °C (75 °F): Switch-off operation in all cases)
b. Vehicle speed >= 50 km/h (31 mph): Switch-off (in all cases)
Vehicle speed <= 15 km/h (9.4 mph): Switch-on if a and c are also fulfilled.
C. Compressor running
(On 960s from 1995 on, the FC is controlled by the engine control module (ECM) instead of the ECC control module.)
Example:
The FC will start when the temperature measured by the sensor on the blower housing is at least 28 °C (82 °F) and the vehicle speed is less than 15 km/h (9.4 mph) and the compressor is running. (However, the FC will not stop unless the temperature falls below 24 °C (75 °F) or the vehicle speed exceeds 50 km/h (31 mph) if the compressor is still running.)
The FC will not start, even if the temperature exceeds 28 °C (82 °F) and the vehicle speed is less than 15 km/h (9.4 mph), if the compressor is not running.
Override control in certain cases
- If the defroster setting is selected, A/C will be engaged in all cases (if the ambient temperature is at least +5 °C/41.0 °F) and recirculation is deselected.
- If max. cooling is selected (and A/C is engaged), recirculation will be engaged in all cases, except when the defroster setting is selected.
- If max. cooling or max. heating is selected, the blower will run at max. speed in all cases if the blower selector is set to auto.
- If the 0 blower speed setting is selected, the A/C compressor will be switched out to prevent icing of the evaporator.
- At high vehicle speeds, the control module reduces the blower speed to provide a constant air flow inside the car. (Under these conditions, air is forced into the car by the ram action' of the air in front of it.) This applies to all blower settings, but not at max. cooling, max. heating or recirculation.
- Compressor switch-in is delayed for 10 seconds when the engine is started. This is to prevent stalling of the engine before the speed has stabilized. (However, the A/C button will be illuminated afier 2 seconds.)
Special functions
The control module will substitute a preprogrammed value for a missing or incorrect parameter.
The control module will restart the program if it should crash'. (This may be caused by the effects of external interference on the electronics).
Parking heater input
The control module is provided with a special input for use when a parking heater is installed. When the parking heater is started, the climate unit is automatically set as follows:
- blower between settings 1 and 2
- floor/defroster
- max. heat