no need lah, coz waste time.
aircon is feeding off power via the belt, putting less power to the transmission. however, unless they have been changed to electric units, water pump, power steering, supercharger, alternator, etc, all also draw power. To switch off aircon until engine is heated up to release some amounts of load while still feeding power to the rest of the accessories doesnt make any sense at all, or achieve anything. one might as well disconnect every damn thing that feeds off engine power. It's too insignificant.
I do not see how an aircon compressor, switched off until the engine reached 75 dec C, is going to help prolong the engine life. What do you mean by prolong? Use it until 500000km? It's certainly insignificant to perform this "switch off" aircon action to achieve this end. I would recommend constant engine oil change, sympathetic use of engine power, proper tuning and servicing of belts, making sure valve springs, cylinder heads, vanos units, crank, cams, + all the millions of little parts in an engine are properly tuned and serviced when you reach a milestone mileage of 200000km or something like that, clearing of carbon deposits, making sure your engine doesnt overheat or run too lean/rich in it's lifespan, to be proper ways amongst many others to prolong engine life.
and definitely switching on aircon only after engine has warmed up is way at the rock bottom of the Engine Life Prolonging Priority List. Dont waste time. One might as well not switch on radio at startup, to help prolong the life of your battery.
