It doesn't randomly turn on lol.
If any of you bothered to read the handbook it says in there.
1. If the air distribution control is in the windscreen de-icing position, the air conditioning system will start operating automatically when the engine is switched on.
2. If the air flow control is in the AUTO position, and air recirculation is selected, air conditioning will start automatically in order to prevent condensation on the windows.
3. When you switch on the ignition, the air conditioning will automatically return to the operating mode it was in when it was last used.
4. If the inside temperature is greatly different from the required temperature displayed and the outside temperature is above 5 °C the air conditioning will switch on automatically regardless of the position of the air flow control. When the ignition is switched on, if the system had been in air recirculation mode, the system will automatically allow entry of outside air unless the temperature inside the vehicle is over 30 °C
But yes I agree, its a complete pain in the arse.
Even worse when the AC don't even work but the damn light still comes on!