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I've got a 30 drive, mostly highway, both ways to work and now that it's getting hotter I'm wondering if it's more economical to ride with a window open, or use the air conditioner?

I'm a fresh air kinda guy, and I would *like* to just open a window but with gas prices what they are, I want to get the best mpg I can.

I'ts going to be one or the other though, I CANNOT take the drive now with just the vents, and it hasn't even really gotten hot yet, still in the high 60's low 70's and we're going to have some 90+ days before it's all said and done.

TIA
 

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( o Y o )
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I had to drive a car w/o air conditioning in florida over 2 summers (it was an 83 and the we cant get the freon for it cuz its illegal). I now drive a focus and have the a/c on most of the time, havent noticed a diff in gas mileage. Mythbusters tested this with 2 expeditions, 1 with a/c on and one with all windows open at 45 or 50 mph. The one with the a/c on died first even though everyone thought the one with windows open would have first because of the extra drag from the open windows.
 

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I always ride windows down.. A/C robs to much power from the Engine when its on. But really it doesnt have much effect with steady highway driving. Fuel economy will be the same on or off.
 

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i had read a test done on this and it turned out to be better mpg with the a/c on actually due to the drag from the windows being opens , you dont have to hqave the a/c on full blast bc the climate in the cabin will eventually be to what your comfortable with and with just need a low power to keep it there along with the car moving at a steady speed....
 

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TwighlightBlueZx5 said:
i had read a test done on this and it turned out to be better mpg with the a/c on actually due to the drag from the windows being opens , you dont have to hqave the a/c on full blast bc the climate in the cabin will eventually be to what your comfortable with and with just need a low power to keep it there along with the car moving at a steady speed....
if the a/c is on it does not matter how high it is. the a/c is only on and off. the fan speed does not affect gas milage or power. so if you use the a/c dont be shy to crank it up.
 

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"if the a/c is on it does not matter how high it is."

Not true at all. The compressor cycle time is altered by how fast the heat is taken out of the heat exchanger in the HVAC system, and the faster the fan speed, the faster the heat is taken out. The more time the compressor is on, the more negative impact on fuel economy.
 

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there really isnt much "drag" when driving with the windows down, especially at anything close to legal speeds.

basically, when I'm in town, driving less than 50 mph, windows are down, if I'm on the highway, it's windows up, A/C on.
 

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Capt. Urn
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i always drive with my windows down, but thats cause i love the feel of the wind in my face.

i have heard that at highway speeds, the mpg pretty much evens out. i think you would see more differance in stop and go driving, as others have said.
 

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Here's a couple of bit of real data, vs. opinion:

"* Several sources claim that closing windows and using a car's air conditioner will provide better fuel economy at freeway speeds than leaving the windows open without the air conditioner. However, FSEC tests showed this in not the case. In repeated evaluation at 65 miles per hour, our test car experienced 11% better fuel efficiency with no A/C and the windows open than using the air conditioner. We also found that closing windows at freeway speeds improved fuel efficiency by 2-3%.

* Other tests done more recently by Edmunds.com showed similar results to those from FSEC: open windows without air conditioning at freeway speeds was, in fact, more efficient than closed windows with air conditioning: http://money.cnn.edmunds.com/ownership/driving/articles/106842/article.html
"
 

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what do you guys call hot......it gets to 150 where i live?!?


70 is the best weather that we have :)
 

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DTF
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i go for both, it depends on the situation

edit* if i were worried about gas mileage i wouldnt have spent so much money on performance parts. thats right, this little beast is my "race car". at least thats what i tell the ladies!
 

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penguin said:
"if the a/c is on it does not matter how high it is."

Not true at all. The compressor cycle time is altered by how fast the heat is taken out of the heat exchanger in the HVAC system, and the faster the fan speed, the faster the heat is taken out. The more time the compressor is on, the more negative impact on fuel economy.
Ok, Thanks, i guess i worded that poorly. The compresser is indeed only on or off though. yes?
 

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that show MYTH BUSTERS on discovery channel tested this....and their results showed almost no difference with either a/c on or windows down...they ran the same car with a full tank of gas around a track at the same speed ...once with the a/c on, and the 2nd time with the windows down and no a/c and they ran out of gas after the same amount of laps.......i do both myself...depends on the damn new orleans humidity....
 

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eatstoomuch said:
Ok, Thanks, i guess i worded that poorly. The compresser is indeed only on or off though. yes?
Yep, and the AC will cycle more frequently the lower the temp is set. Our vehicles have a little bonus though- thanks to modern engineering. Our AC compressor is limited to the # of rpm's it will turn, and will cut off at WOT. The first bonus is longer compressor life, the second bonus is that it won't rob power if you need it for acceleration. I imagine that there is some sort of rpm limiting at higher non-WOT engine speeds also which means less drag on the engine.

I am not sure if the recirculation setting (AC Max) affects compressor cycling like in older US cars. If not, then I'd definately keep the system in recirc mode while the AC is on.

A good common sense idea that hasn't been listed here: If you prefer to have your AC on while driving, leave it off for the first 2 minutes of your trip and roll down all the windows to release trapped hot air.
 

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"The compresser is indeed only on or off though. yes?"

Yes, but the percent of time it is "turned on" depends upon how "high" you have the A/C set. The A/C control system does this automatically. The faster heat is taken out by the system, the more time the compressor is actually "on," and the greater the impact on the fuel mileage.

I'm not an A/c man, but I believe that GM cars in the past, and perhaps even today, had a more complex variable output compressor which used a "swash plate" to vary the output. With that design one could actually vary the output and not have to cycle it on and off to approximate the appropriate output. But I'm only 50% certain of that little factoid.
 

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That all does not seem right to me. The a/c has to always be loading the engine when you turn it on, as far as i knew. i never turn it on at high rpms, i have seen that throw a belt in a car before (an older one though)

anyhoo not trying to argue just getting the facts sorted out
 

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The car automatically turns the A/C of when you hit high rpms. Thats why when you floor it, then let off you notice instead of nice cool air, you get hot air. The car automatically does this to give you the extra power that the A/C robs.
 
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