3315699 - E5020 ENGINE COOLING - Functional description

Functional description

The power supply to both fans N11 and N12 (always operated in parallel) is controlled by two external relays J30 (1st speed) and R6 (2nd speed), located inside relay control unit B3. When fans N11 - N12 are supplied by relay J30 (1st speed), the supply line is subject to resistance loads O10 - O12, that reduce actual supply voltage and thus speed; if the fans are operated by relay R6 (2nd speed), this is activated by maximum battery voltage, which corresponds to maximum speed. Both relays are supplied with power directly from the battery - junction unit A5 - by a line protected by a special fuse B8 for J30 (external) and F8 for R6, inside B3.

They are energized by an earth signal coming from four-stage pressure switch K10 via the engine control unit M10.

• if the coolant temperature reaches the first temperature stage, or the 4-stage pressure switch K10 - pin 3 - indicates to control unit M10 - pin 52 of connector A - that the first pressure stage has been reached, control unit M10 sends a signal to 1st speed relay J30 from pin 20 of connector A.
• If the engine coolant reaches a higher temperature level or the 4 stage pressure switch K10 (pin 3) signals to the control unit M10 (pin 51 of connector A) that a high pressure stage has been reached, then the control unit M10 sends an earth signal (from pin 19 of connector A) to the 2nd speed fan relay R6.