The compressor engagement circuit is controlled by relay F5 housed in the engine compartment junction unit B01.It is supplied by the direct line from the battery entering pin 1 connector A of the junction unit and protected by fuse F19.The coil for relay R5 is supplied by the signal coming from relay R9 which, in turn, receives a direct supply from the battery from pin 1 connector A.The supply for the coil for relay F9 is ignition-controlled (15/54) and arrives via a line protected by fuse F16.Relays R9 and R5 are energized by an earth signal coming from the engine management control unit M10 from pins 15 and 41 respectively of connector A.In this way the control unit M10 controls the engagement of the air conditioning compressor L20 via relay R5.The engine control unit M10 connector A receives the 4 stage pressure switch K10 signals for engaging the radiator fan:- operation at first speed from pin 35;- operation at second speed from pin 21;- engagement of the air conditioning from pin 48.