Can someone explain.....................

[blackcat77]

To settle a dispute - my OH says that you do not use up any more fuel by having the air-conditioning on. I say you do, based entirely on Jeremy Clarkson driving a car to Scotland and back on one tank of fuel (several series ago) and not having the radio, heating, or any other gadgets on and somehow he managed it! So which of us is correct?

[Postdog]

I agree with you, but then I saw that too....

Mind you it's logic isn't it? The engine drives the car and charges the battery at the same time, so if the battery doesn't need charging to replace lost battery power through having gadgets on, then the engine power is used just for driving. Basic physics say that energy can't be created, only changed to a different type of energy, so it stands to reason that using gadgets requires the engine to work harder, and the engine itself can only do that by using more fuel.

Probably not explained it well, but yes, I agree with you.

[Ethel]

Both right.

Use the air-con sparingly. Air conditioners can use about 10 per cent extra fuel when operating. However, at speeds of over 80 km/h, use of air conditioning is better for fuel economy than an open window.

[greenrook]

Don't know about 'haven't explained it well', postdog, I think your exposition is an absolute model of clarity. Thanks, I never really grasped the fuel/airconditioning thing before - Greenrook

[blackcat77]

I think that you explained that very well, Postdog, and thank you as well Ethel. When you put it like that it makes perfect sense. Mind you, we haven't had to use the air-con very much this year!

[colin6789]

Just a point , although using Air-con will use more fuel, if you are travelling at any great speed, having the windows open will use more fuel.

In some areas if you are travelling slow with the windows open you will loose your bag, wife, kids, life, car, delete as appropriate, and your insurance will be invalid.

[LCDMAN]

This was covered in depth on Mythbusters on the Discovery channel. After extensive testing they concluded that at less than 40 mph then opening the windows and using the aircon had a similar tiny effect on fuel economy. Over 40 mph the effect was greater, using the aircon DID reduce the fuel economy slightly (down from 38 mpg to 36.2 mpg). by it was MORE economical than opening the windows, In conclusion, by experimentation, Yes, putting on the aircon does have a detrimental (albeit small) effect on the fuel economy.

[Toureman]

The main reason the A/C uses more fuel is because around 5% of the fuel that could run the engine is used on powering a compressor.

Just as electricity is used to power a fridge.

[eastern]

One thing you will notice, especially on small engines (1.4 size) is the lack of power when the aircon is on, you therefore drive the car harder to get the power you need. On my peugeot 206 I used to switch off the aircon when I wanted to overtake! Another thing to remeber is to use the aircon at least once a fortnight, there is a lubricating oil in the gas and that keeps your pump lubricated and will prolong its life. Another tip I was told was always start your car with the aircon off as the aircon compressor does put a load on the engine. The best way to improve your fuel economy is to improve your driving! you can easily improve your economy by 10% just by carefull use of your right foot!

[ianglyn]

yes it does use up more fuel...
when you put it on its like a pully putting presure on the fan belt.so it would be pulling a slight presure on the engine..