Does turning on the air conditoner in the car waste more gasoline?

Question

you know how people say turning it on waste more gas? so when people are low on gasoline they dont turn the air conditioner on? is it just a myth? or a real fact?

Answer 1

On mythbusters, they showed that it depends on the speed of the vehicle. From their graphical calculation, they determined that a speed of about 45mph was the break point.

Driving less than 45 mph, windows down was more efficient.

Diving more than 45 mph, windows up and A/C on was more efficient.

However, the most efficient obviously is with windows UP and A/C OFF!

If you understand Forces, you'll know that drag forces are directly proportional to the square of the velocity. Which in laymans terms says that that faster your going, the drag forces will dramatically increase.

ie, if you're going 10 mph the drag force is proportional to 10*10 = 100, if your going 30mph the drag force is proportional to 30 * 30 = 900. So by going only 20 mph faster, you've almost increased the drag forces by 8x.

Answer 2

The A/C does not waste water or freon. The a/c has nothing to do with water. The a/c is a closed system that cycles freon. However, in order to get rid of excess heat, the refrigerant must be compressed with a compressor. This takes power to do so, and that power comes from the engine. So to travel the same speed when you don't have the a/c engaged, takes more power or more fuel. And it does not make the engine less efficient. The engine efficiency has nothing to do what it operates. It just means you are using less of the engine's power to move the car. It has nothing to do with the batter, like some people are saying. The compressor is generated by mechanical power from the engine, not electricity. And the only reason those studies show you use less fuel than just having the windows down, is because those tests were done at high speeds. The aerodynamics of the car are worse with the windows down. Therefore, the loss of power due to the a/c is less then the loss of power because of high drag, but only at high rates of speed. At low speeds, the aerodynamics have little effect on vehicle drag, and the a/c will be more dominant.

Answer 3

I've seen copied reports on this site that suggest the aerodynamics on a car is better with the windows rolled up with the air conditioner on.
I'm a skeptical old fool because: When an AC clutch engages on an air-conditioner the engine RPM drops with the added load placed upon it. That soaks up horsepower and fuel. If they had tested more cars maybe I'd change my mind. Till then I'd use the AC sparingly.
Aerodynamics don't really come into play unless the vehicle is shaped well anyway. Particularly when driving under 40 mph with the AC on your going to use more gasoline.

Answer 4

Just so everyone knows, hsueh010 ^^, is wrong about the drag coeficent. Its not the square of the speed, its the cubed of the speed. Heres what its like
1 mile an hour = 1*1*1=1
2 miles an hour = 2*2*2=8
3 miles an hour = 3*3*3=27
4 miles an hour = 4*4*4=64
5 miles an hour = 5*5*5=125
and so on.

So when your going 70 down the highway, the drag is 70*70*70= 343000.

Answer 5

it is a real fact - turning on your compressor uses more gasoline - just as your home air conditioner uses more electricity -

Answer 6

Myth, drag is lessened by rolling up the windows. This only applies to highway speeds though!

Answer 7

Sure,and it puts more strain on the engine,but it is worth it to me.The question is,do you want to save a little gas,or swelter.

Answer 8

yes it does, the air condition needs a large amount of power to keep it running.

Answer 9

not by much