Does using the AC really really use more gas in your car?

Question

Being extra humid the last few days and with the cost of gas being so high I rally want to know am I burning a bigger whole in my pocket by turning on the AC and is it burning even more if the AC is on high?

Answer 1

Yes, having the a/c on will burn more fuel than with it off. The a/c uses a compressor to compress the refrigerant used for the a/c system. This compressor runs off of the crank shaft so it takes away some of the power used to move the vehicle. When you are driving the car keep the accelorator pedal steady and turn on your a/c. You should feel a slight jump that results from the a/c compressor engaging. You'll also notice your velocity decrease slightly. If you want to maintain your previous velocity, you'll have to give the engine more fuel. This is were your decreased fuel mileage comes from. However, the cost difference you will experience by using the vehicle without a/c compared to with a/c will not be that significant. I say, stay cool. If you are really curious. Drive a week with a/c and the next without a/c and compare your fuel mileage difference.

Michael M says that the pullies are all operation whether the a/c is on or not. This is correct. But if the a/c is not engaged, the compressor is not drawing any power from belt. So it acts almost like an idler puller.

Another user said that the engine is hotter and that is why more fuel is used. This is not correct. The increased fuel consumption is from the extra power need to run the compressor. The engine will get hotter, but that is because the engine's power output increases, which means more waste heat is generated.

Answer 2

Yes, A/C uses more fuel. If you think about it, the A/C compressor is a big pump that pumps coolant through the condenser and the passenger cabin to cool the car. It takes energy to make that pump push the coolant through (it is at high pressure). So the engine uses some of it's available power to turn the compressor to cool the cabin.

Now, I read somewhere in a car magazine (can't remember where now, maybe Car and Driver) that they compared the fuel usage of a car with A/C on and a car with A/C off and the windows rolled down. The results were that the aerodynamic drag of the windows rolled down make fuel economy worse than running the A/C. So, run the A/C if you're hot. I see about a 2 mpg drop in my fuel economy with my A/C on. On a hot day, it's worth it!!!

Also, the A/C compressor has a clutch that only engages when the A/C is turned on. So the person who claimed the A/C is used whether you run it or not is completely wrong. In fact, you can even see the clutch engage and disengage by watching the compressor when the engine is running and having someone turn the A/C on and off.

Answer 3

True, the drag from opening windows makes you lose as much as running the AC on most models. On many new cars the AC only take 1 to 2 MPG. Don't use it if your trip is so short the car never really cools off anyway. Keep tires properly inflated. Remove all the "stuff" from your car - extra weight takes more gas. Take your foot off the gas when you see red taillights ahead and coast instead of rushing up close and hitting the brakes. Try not to come to a full stop - unless at a stop sign - since it takes more gas to get back up to speed while in low gear. Carpool. Park right at the entrance to the shopping area or store instead of driving around looking for the closest parking space; the walk will be good for you, too. Keep close to the speed limit; consumption goes up when you go over 70.

Answer 4

Anything that makes your engine turn with more resistance will cause it to use more gas. Going up a hill that's a harder load, more gas. Running the lights and other electrical things makes the alt. harder to turn and a little more gas, though it would be slight.

A/C, big user of gas. Just sit at an idle, turn it on and listen to your engine slow down a bit for a second.

But, given the fact that it may save you a buck or two not to use it, is saving 5 or 10 dollars a tank worth suffering in the heat.

Answer 5

Not enough to worry about. As a matter of fact at highway speeds the drag from having open windows would be more wasteful than having the A/C on. I suppose if you were truly motivated you could drive along without A/C and the windows up and get the most for your gallon of gas, but in real life and at summer temps do yourself the favor and enjoy your A/C!

Answer 6

I did the math ...if u get 30mpg wo ac and 28 with ac...on a 100 mile drive u save 73 cents.....now concider u paid about 1000 dollars to haves ac in ur car.... do what u want but i use heat in the winter and ac in the heat....im not gona sweat myself up over a few pennies

Answer 7

it uses a little it more,but not enough to worry about really,id rather spend the extra few pennies it uses as burn up in a hot car,rolling the windows down doesn't really help save gas either,it creates a wind pocket and takes more gas to run the vehicle,so either way its going to use gas,id just use the air,good luck.

Answer 8

Yes, it really really does use more gas.

The engine has to work harder to turn the AC compressor, making it run hotter, which burns more fuel.

Answer 9

Yes.

Our Landrover uses about 2% extra fuel if we have the AC on all the time.

The fuel is needed to drive the regridgerant unit and the energy has to come from somewhere.

Answer 10

Not enough to worry about. Driving with the windows down consumes extra fuel because of the aerodynamic drag the open windows creates. Just use your a/c and be comfortable.