When conditions require, the climate control system control unit switches on the air cooling and dehumidification circuit, activating the air conditioning compressor.The special button in the climate control system control panel enables the operation of the air refrigeration circuit; the LED comes on when the button is pressed.The above button enables operation of the air cooling circuit, but actual compressor activation is dependent upon the climate control system control unit logic: for more details Characteristic of working principle 5040 AIR CONDITIONING CASING AND COMPONENTS.The compressor can also be switched off through the intervention of the 4 stage pressure switch or by the engine management control unit Characteristic of working principle 1056 PETROL INJECTION SYSTEM.The compressor is controlled by means of a special relay located in the engine compartment junction unit; the supply line is protected by a special fuse located inside the engine compartment junction unit