Cooling Fan Description and Operation (Diesel)
Cooling Fan Description and Operation (Diesel) |
The engagement of the different steps is depending either on coolant temperature or A/C pressure. If the coolant temperature is too high at ignition off there will be an afterrun for maximum 2 minutes.
At step 1 (lowest speed) ECM activates relay K9 in UEC and the fan motors are in serial circuit. One motor is without pre-resistor, the other one with pre-resistor.
At step 2 ECM activates the relays in the relay box and both fan motors are connected in parallel. Both motors have pre-resistors.
At step 3 ECM activates relay K9 in UEC and the relays in the relay box and the motors are in serial circuit, one with and one without pre-resistor.
At step 4 ECM activates K9 and K13 in UEC as well as the relays in the relay box and the motors will be in parallel with no pre-resistor.
Refer to Engine Cooling Schematics .