dojj quite right. except the fan bit. if you don't have a massive electric fan putting air through the a/c condenser, the pressure will rise very high making the compreesor use more power and for the system to work very ineeficiently. the heat that you take out of the cabin air has to go out of there

the compressor has an electromagnetic clutch so it doesn't use any power when switched off (except from a fraction of 1 hp to turn the freewheeling pulley with the belt). trust me on this, i've worked for an aircon compressor manufacturer for over 10 years