Relays T1 and T2 of engine compartment control unit B1 and external relays J29 and J30 manage the operation of both fans N11 and N12 at four different speeds: the coil power lines are protected by fuses F12 and F13 , also in engine compartment control unit B1 .If the engine coolant reaches the first temperature level or linear sensor K120 indicates to the control unit M10 pin 13 of connector A - that a certain pressure level has been reached, control unit M10 sends a signal from pin 90 of connector A that excites the fan 1st speed relay T1, which then sends power to fans N11 and N12 that are joined in series via switch J29: both fans thus turn together at the first speed.The linear sensor K120 receives a power supply and reference earth from the engine management control unit M10, pin 12 and 22 of connector A.If the engine coolant reaches the first temperature level or linear sensor K120 indicates to the control unit M10 - that a certain pressure level has been reached, control unit M10 sends a signal from pin 69 of connector A that excites the relays T20, J29 and J30, which then send power to fans N11 and N12 via additional resistances O10 and O12: both fans thus turn together at the second speed.If the engine coolant reaches the third temperature level or linear sensor K120 indicates to the control unit M10 - that a certain pressure level has been reached, control unit M10 sends a signal from both pin 90 and pin 69 of connector A that excites the relays T1, T20, J29 and J30, which then send power to fan N11 directly and to N12 via additional resistance O12:If the engine coolant reaches the fourth temperature level or linear sensor K120 indicates to the control unit M10 - that a certain pressure level has been reached, control unit M10 also sends a signal from pin 94 of connector A that excites the relays TT1, T2, T20, J29 and J30, which then send power to fans N11 and N12, which then turn together at maximum speed