Relays T6 and T7 of the engine compartment junction unit B1 manage the switching on of the two speed fan N11: the coil power lines are protected by fuses F6 and F7 , also in engine compartment control unit B1 .Both are energized by an earth control signal coming from the engine management control unit M10.If the engine coolant reaches an initial temperature level, or the linear sensor K120 signals to the control unit M10 - pin 13 of connector A - that a certain pressure level has been reached, then the control unit M10 sends a signal - from pin 90 of connector A - which energizes the 1st speed fan relay T6 which sends the power supply to the fan N11 via the additional resistance O10: the fan turns at the first speed (slow).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 a higher temperature level, or the linear sensor K120 signals to the control unit M10 - pin 13 of connector A - that a higher pressure level has been reached, then the control unit M10 sends a signal - from pin 69 of connector A - which energizes the 2nd speed fan relay T7 which sends the power supply directly to the fan N11: the fan turns at the maximum speed.