Why do cars burn more gas with the air condition on?

Question

can anyone help me to understand the mechacism of the air condition and how it relates to gas usage

Answer 1

More power required to run the a/c compressor (about 3 hp), fan motor uses electericity, more power required to make electricity!  Yes the alternator spins all the time, but it pulls more power when making elcetricity,( than when just "spinning")!    In order to provide more power, the engine burns more gas!

Now the difference in mileage might be 2-3 mpg on a car that  gets 25mpg, - so the question here is are you willing to "roast" for that extra mile or two!....This is a good thing to know however if you are out in "boonies" somewhere, and it appears you may not be able to make it to gas station before the car might run out of gas! ... Slow down about 10 mph (from 65-70 as speed limits allow), - turn off a/c and accelerate slowly ,"coast" -by letting foot off gas a little going down hill (if you loose 5mph) - it is not that hard to pick it back up just before incline levels out! You possibly could make an extra 5 miles, - which beats walking!

Oddly enlough the older cars with the bigger heavier engines (that get less mpg) ,-- also have less decrease in fuel mileage, as the very large engines work less to pull that extra hp out running a/c compressor!

The way you drive also costs you horsepower!  Most people still stick with "squirly driving",-- which possibly uses more than a/c when driven smoothly, and skipping the jackrabbit starts!

Answer 2

It uses more gas because the engine has to expend extra energy to turn the A/C compressor.

The compressor is turned by a belt, just like the alternator. Look under the hood, and you will see one or more belts wrapped around a series of pulleys. The engine uses the belt(s) and pulleys to operate different things such as the alternator, power steering, etc. One of those pulleys is attached to the A/C compressor. When you run the air conditioning, a clutch on the compressor grabs that pulley, making the inner workings of the compressor turn. The engine has to work harder to run the compressor than it does when the compressor is off.

Answer 3

Instead of using power to move the car the A/C compressor uses power to move heat out of the car. A/C does not cool air it removes heat.

Answer 4

The engine needs a certain amount of fuel to push the car forward at a given speed.  When you add the air conditioner to the mix you also add an aditional energy requirement.  That means more fuel has to be used to get the same speed with the additional equipment running.