Inside the engine goes like this. At idle you use little fuel because it only has to maintain about 600 RPM. When you drive at 60MPH your engine is running at about 2000 RPM and needs more fuel to do it. Want to go faster need more fuel pull heavy loads use more fuel want more horsepower need more fuel. It is a heat engine it uses fuel for that heat.
It uses more fuel going somewhere. However, the fuel efficiency of the engine drops like a stone near idle (after all, at idle all the energy of the gasoline does noting useful) because of a technical consideration called the Carnot ratio and because of "pumping losses" - the energy needed to pull air past the nearly closed throttle. The A/C adds useful load but at exremely low efficiency.
However, efficiency is not the same as consumption. It does not take a lot of energy to run the A/C (1-4 hp, depending on temperature, humidity, size of vehicle...). It takes even more energy to drive somewhere, but the efficiency is higher. Bottom line: it costs more to drive than to idle with the A/C on, it costs more to idle with the A/C on than to idle with the A/C off, and it costs more to idle with the A/C off than it does to just shut the engine down. At the end of the day, it is your money to spend as you please.
man really you need to get a better hobby
when i search for answers i got idling of V6 and 2 litre to 3 litre engines ya sure they consumes more fuel but my question is about just an 800 cc suzuki alto , here the situation is too hot so vehicle is left idle with AC on when we wait for someone or in traffic , so my question is if i idle the car for an hour or if i travel to some place for an hour the fuel consumption is same or not? and what's happening technically inside the engine
