Radiator fan: Notes
The Saab 9 -3 is equipped with a radiator fan to keep the coolant within definite temperature limits. Depending on the market, the cooling fan may be of either 1-speed or 2-speed type. The 2-speed fan runs at high speed and low speed.
If the car is equipped with A/C, the radiator fan is not controlled on the basis of coolant temperature alone. Several other parameters are also taken into account:
- Coolant temperature (bus from MIU)
- A/C pressure (own pressure gauge)
- Car speed (bus from MIU)
- Outside temperature (bus from SID)
- A/C system status (active/inactive)
The information is used in DICE and determines whether the radiator fan is to be started or stopped and whether it is to run at high speed or low speed.
To maintain idling speed at a constant level, DICE sends information on the estimated current consumption. This information goes via bus to the engine management systems and is sent 0.1 seconds before DICE switches the radiator fan on or off.
To understand the operation of the radiator fan, it is important to note that it can be activated differently at the same value (within certain given limits), depending on whether the value is rising or falling.
Even after the engine has been switched off the coolant could still overheat and for this reason DICE can start the radiator fan up to 20 minutes after the ignition switch has been turned to OFF. In such case the radiator fan can only run at low speed and for a maximum of 3.5 minutes. The coolant circulates through thermosiphon action after the ignition switch has been turned to OFF.