Fuel consumption & Air Conditioning !

Is it true that when you use Air Conditioning you get poor gas mileage? I was told this recently. It is the first time I have a vehicle that has Air Conditioning a 2006 3.3L Dodge Caravan.

I am told when you turn on the Air Conditioning you can feel and hear "something" kick in, in the engine compartment.

If the above is true and I am assuming it is, please educate me as to how Air Conditioning and gas mileage is related.

Thank you in advance. Denny B

Reply to
Denny B
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A friend of mine did a test. He said he used more gas with the windows open and the air conditioner off, than with the windows closed and the air conditioner on. So try the later. I don't know what the air conditioner scientists say.

Reply to
boxing

Sure. The air conditioner takes a lot of energy to turn it. It's a lot more powerful than a little window airconditioner in your home.

Yes, when you turn on the air conditioner, you can feel the engine slow down because more load is being thrown on it.

It takes energy to turn the compressor. That energy has to come from somewhere. Burning gasoline is where it comes from.

Anything that puts more load on your engine will reduce your mileage. Driving uphill will give you poorer mileage than driving downhill. Second law and all that...

--scott

Reply to
Scott Dorsey

That's a different issue... because opening up the windows increases the body drag, which consequently will require more throttle on the engine to keep the car at speed.

How much more depends a lot on the car... and if it's a VW Bug, opening up the little vent windows will actually _reduce_ the body drag a little.

--scott

Reply to
Scott Dorsey

It depends on what speed you are going, under roughly 40mph the air con will use more fuel than the drag form having the windows down will, above this though the drag on the car from the windows being down will be more than the extra fuel used by the air con.

Nick

Reply to
Nick Bourne

Of course running the air conditioning reduces mileage! Air conditioning requires an input of energy to function, and that comes from burning a little additional fuel. Its simple conservation of energy! ANY device that you turn on in the car will affect mileage somewhat, although the change may be far too small to measure as in the case of, say, the radio. Turning on the headlamps draws about 100-150 watts of power from the alternator, which increases the load on the engine, and burns a tad more fuel (which is why daytime running lights should be banned- it may not amount to more than a pint of fuel per week per car, but multiply that by a few hundred million cars and it adds up). Air conditioning is a bigger load, and draws more energy. Rear defrosters are a pretty big load and draw more energy. What you "feel kick in" is the compressor engaging, and it draws a few horsepower from the engine when its running.

With AC, however, there's an offsetting effect- when you roll the windows down you add aerodynamic drag, so at highway speed you might actually use less fuel with the windows up and the air on than you would with the air off and all the windows open.

Reply to
Steve

Not necessarily 'poor', but it may decrease slightly. I doubt you will go from 20 MPG to 12 MPG...for example. Maybe from 20 to 19.5...not enough to fuss about.

Heat in your car uses "free" heat the engine is already producing, A/C requires energy to drive a compressor. And of course that energy has to come from the engine.

If you research how auto air conditioning and heating work, this may make more sense to ya...

I've been told many times, that at highway speeds, the aerodynamic drag created by having the windows open negates any savings from not running the A/C.

You also have to consider the factors of passenger comfort, screaming grumpy hot kids, arriving at your destination cool instead of hot and sweaty, etc. That's worth something, too, right?

You're mileage isn't going to be that great anyway, in that vehicle...A/C or not. Run the A/C and enjoy it. Your nerves and your passengers will thank you.

Don Byrer KJ5KB Radar Tech & Smilin' Commercial Pilot Guy Glider & CFI wannabe kj5kb-at-hotmail.com

"I have slipped the surly bonds of earth; now if I can just land without bending the gear..." "Watch out for those doves..."

Reply to
Don Byrer

Sure, it probably gobbles 2 to 3 mpg. And yes you could save some money by not running the AC. Just as you could save some money by not running the house AC in summer and the furnace in winter.

Said another way there is a cost to comfort.

Reply to
John S.

Running the A/C does decrease fuel economy. Your A/C is doing work (removing heat from the passenger compartment). In practice, I think it is hard to find the change in mileage. I keep detail fuel purchase records and looked back over them to see if I could see any significant difference in fuel mileage in summer and winter. I couldn't. And here in NC, I run the A/C all the time in the summer. My conclusion is that the amount of energy being consumed by the A/C is trivial, so I quit worrying about it. The Mythbusters on TV tried to answer the question of whether you got better mileage with the windows down and A/C off, or windows up and A/C on, but they screwed up these test so badly the results were meaningless (the highway speed used was too low to be representative of the real world).

Ed

Reply to
C. E. White

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