How does AC, in a car, use gas when it runs off of electricity from the aldernater?

Question

yeah i think i spelled aldernater wrong, but that's not the point.

if the AC runs from the electricity that the aldernator makes, then why does running AC use more gas? the aldernator and belt all run at the same speed, it doesn't slow down or anything, and the extra electricity that is made from the aldernator is sent to the AC unit. so why would running the AC use more gas? the aldernator doesn't spin faster to generate more electricity. so just why would running AC use more gas? wouldn't it just use the same amount?

sorry, i've just been stuck on the question for days and i can't find my answer anywhere! i asked my dad, and he just kept going in circles and just wouldn't give a straight answer (lol i can tell he doesn't know! but he works on cars quite a bit and i would think it's something he'd know). but anyway i hope you guys can help me out with this. thanks!

11 points to best answer!

Answer 1

Using the air conditioning in a vehicle turns on the compressor which makes the engine work harder to run this component of the car along with the other parts the engine is already running. The harder the engine works the more gasoline or fuel that it needs and uses.

However if you are comparing using the AC on the car to rolling down your windows there may not be a difference in the amount of gas used. Rolling down the windows and driving puts drag on the car and again makes the engine work harder to overcome the drag coefficient and thus uses more gas than if the windows were in the up position.

Answer 2

The a/c is driven off a belt which runs off the motor. In todays cars, you really dont use much more gas at all. You used to feel the a/c kicking in and out.

Actually, mythbusters did a test, and you get worse mileage with the windows down

Answer 3

a/c uses more fuel because it requires the engine to work a lil harder to power the a/c compressor the a/c is powered by the pulley system on your vehicle the alternator is set to recharge a certain amount of amps but not to get away from your question more power is required by the engine when the a/c is on but studies show that using the a/c is about the same as riding with the windows down but wont affect  gas mileage enough to really notice maybe if you logged all year your fuel consumption with and with out it on i hope this helps  

Answer 4

The air condition system containes a compressor which is a pump. The pump is driven by a belt. The crankshaft turns this belt which also turns the compressor pulley. This compressor takes energy to turn it (parasidic drag) which take more fuel to burn to create the work. In other words, the engine drives the air condition pump.

Answer 5

Because in order for the alternator to turn and make electricity, the engine has to be running. In order for the engine to be running, the car has to be running. In order for the car to be running, it has to burn gas.  

Answer 6

Almost all cars run the AC from a belt on the engine, and it uses gas. My car MPG drops from 28 to 26 MPG on the open highway when the AC is on.

Some new cars, like hybrids, have the AC running from the battery, and that still takes power, more power actually, from the car engine, as it has to run the alternator to keep the battery charged.

Your arguments are specious. Using electric power from the battery means the alternator has to work harder to keep the battery charged, and that comes from the alternator putting more drag on the engine, which uses more gas.

Bottom line, you don't get something for nothing. The power has to come from somewhere, and that is the engine.

.

Answer 7

If you look under the hood of the car, you'll see the fan belts, either one serpentine wide belt or two/three of them. One of the belts is looped around the AC compressor unit which propels the freon through the AC unit's hose system. This belt is also looped to the main cam wheel of the engine that is moved by the actions of the pistons when the gas/air mixture is "exploded" by the spark of the spark plug. The AC motor is electrically activated through the alternator and or the battery. You can hear the AC compressor working electrically by the clicking noise with the engine running and the AC on. Essentially, the AC can run on the battery alone but it is the fan motor only and you won't feel any cool air unless the engine is running. So to get cool air, the engine has to be on, and the engine uses gas to run.

Answer 8

the ac isn't really just running of the electricity of the alternator. it has its own pully that runs the compressor that is driven by the engine. by turning on the ac, it engadges the pully which adds an extra load to the engine, takes away a minute amount of rotational energy from the motor.  

Answer 9

The A/C has several parts. The electric fan that blows air into the cabin is just the same fan that blows heat in from the heater. However, you also have a compressor, which is basically a mechanical pump that is driven by the motor. This pumps R134a gas through the coil, which cools it, then the fan sucks air through it, which cools the air and brings it inside the car.

That's oversimplified, but you get the idea.

The cars engine has to turn the compressor, so it has to work harder when the A/C is on.

Answer 10

it creates engine drag making the engine work harder therefore burning more fuel.

Answer 11

the reason why it uses more gas is because your ac compressor is belt driven. when the clutch is engaged on the compressor it takes power to turn. if u took the belt off your car and turned the alternator by hand it will turn freely   leave the belt off and just turn the key on and not start it turn the ac switch like you was fixn to drive and try to turn the compressor it will b like its locked up and it will take more power to turn it by hand.  the more power it takes the more fuel it takes. kinda see what i sayn.

Answer 12

The AC COMPRESSOR takes about 10 Hp to run..it is not electrical it runs off a belt and uses power from the engine......

Answer 13

Using a/c requires motors to work harder belts most turn more rpm

Running your air conditioner does cause your vehicle to consume more fuel, but driving with your windows rolled down can be even worse due to the increase of drag on the vehicle. If you are driving slowly, such as around town or in city traffic, then you are better off leaving your windows open, if at all possible. For highway driving, roll up the windows and turn the air conditioning on.

Answer 14

A/c is not run from the Electrical of the car the clutch to the A/C is and the accessories connected to the A/C. the A/C is really driven by the motor as a pully, much like the alternator. the A/C pushes presureized gasses and fluids through the system and this draws a fair amount of horsepower from the motor.

Answer 15

Running the AC uses more gas because the alternator has to work harder to keep up with the demands being put on it, and the alternator is run by the motor whch uses gas to make it go.  So therefore, everything has to work harder to meet the demands when the AC is on, which means you use more gas to make it all go.  Hope that helps, if not I can try to be more specific.