1) Affect =/= effect. Learn the damn difference.
2) At normal city speeds, the AC decreases fuel economy.
3) At highway speeds, you generally approximately break even, so no reason not to use the AC.
4) Ricers drive with the window down to share thier sh!tty techno or bad pop-hip-hop music with everybody around.
2) At normal city speeds, the AC decreases fuel economy.
3) At highway speeds, you generally approximately break even, so no reason not to use the AC.
4) Ricers drive with the window down to share thier sh!tty techno or bad pop-hip-hop music with everybody around.
Transfering the parasitic drag from a compressor to the alternator doesn't really solve the problem.
High and low fan settings make a difference in how often and the length of time the compressor cycles, especially if it's in recirculate (MAX-AC) mode, so it can make a difference. For best efficiency, set the air to recirculate (or MAX AC) and the lowest fan speed that keeps you comfortable.
In city driving the AC will decrease milage dramatically, especially on cars less than 15 years old. (after they changed the type of freon used to one more "environmentally friendly" - yet it has 2.5x the impact on milage/horsepower leached....)
With highway driving it's not such a big hit. But if I'm moving at highway speeds I'd rather get fresh air coming in through the windows than AC.
With highway driving it's not such a big hit. But if I'm moving at highway speeds I'd rather get fresh air coming in through the windows than AC.
- Mar 20, 2000
- 102,402
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ummm... no, the power used to run the compressor can't just come out of thin air... if you're increasing the electric force you're going to have to increase the drag the alternator makes. and then you won't have the option of turning it off to save mileage.
Nah, they just need to create an alternator with multiple gears it can switch into. High drag when battery needs more charging, low drag at other times.
The drag varies on depending on the current draw. No need for a gearbox. I don't know what ElFenix is talking about... when the compressor is off, there wouldn't be any drag from it on the alternator.
So how come the drain is so pronounced when flipping on the AC, but headlights make no noticable difference?
The headlights and other running lights only use about 200 total watts, if that. That's about 1/4 HP. You typically wouldn't feel that when you turn on the headlights.
I don't know how many BTUs per hour automotive ACs are typically rated at, but a 10000 BTU/hr window AC unit with a very good EER still uses about 1200 watts of electricity. It looks like once 36-48 volt automotive electrical systems start being used, they might be able to make the auto AC a bit more fuel efficient, but you absolutely cannot get something for nothing. The more power drawn from the alternator, the more drag on the engine.
I don't know how many BTUs per hour automotive ACs are typically rated at, but a 10000 BTU/hr window AC unit with a very good EER still uses about 1200 watts of electricity. It looks like once 36-48 volt automotive electrical systems start being used, they might be able to make the auto AC a bit more fuel efficient, but you absolutely cannot get something for nothing. The more power drawn from the alternator, the more drag on the engine.
what if you turn on the option that allows air to be recirculated through the car... and then activate the AC for lets say 5 minutes every half an hour... would this give you pretty "cool" results with less hit on your MPG?
I always do that and I dare you to call my car a ricer
It makes it easier to signal other drivers, the wind gives me a second sense of speed and when I have to put both hands on the wheel, it usually means im going too fast.
-or-
the ac is and windows are up on because I have the girl in the car, in which case i still only have one hand on the wheel
I did a little unscientific experiment with my van in regard to this subject. My data was based off of the real time computer mileage readout. It didn't matter if I had the air on or off, at 78MPH, I got 23MPG on flat roads. It was a calm day and I had the windows up in an Olds Silohette with ~8000 miles and a 3.4L V6. and of course, YMMV
Originally posted by: redly1
I did a little unscientific experiment with my van in regard to this subject. My data was based off of the real time computer mileage readout. It didn't matter if I had the air on or off, at 78MPH, I got 23MPG on flat roads. It was a calm day and I had the windows up in an Olds Silohette with ~8000 miles and a 3.4L V6. and of course, YMMV
Does the mpg reading update immediately when you change speed or does it take a minute? If it's near immediate I can guarantee you the number is just a simple calculation based on your speed and is not truly connected to your real mileage.
He was talking about the hypothetical electric A/C compressor. The A/C in a car is run with the engine, as we all know.
I think it's going to totally depend on your car/engine. But remember, that energy is not free. It isn't created or destroyed. So yes, running your A/C will lower your gas milage.
Whether it's 0.25MPG or 5MPG, will depend on your specific case.. engine/car/driving habbits/weather/fuel blend/penis size/etc.
That is probably true at highway speeds, but for slower speeds the load from the A/C would be greater than the aerodynamic drag due to open window(s).
DrPizza
Administrator Elite Member Goat Whisperer
I've read that it's actually about the same as driving with all the windows open.... Nonetheless, I'm going to go on the record to maintain that whether it uses more gas or less gas than having the windows open is dependent upon the speed the car is driving, since the air resistance would be a function, most likely, of the velocity squared.
10mph, windows open uses less gas
70mph, A/C uses less gas
and, some place in between, there's a tie.
(Oh, and personally, I have the air conditioning on AND the windows open, so there!)
Demon-Xanth
Lifer
- Feb 15, 2000
- 20,551
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It depends on the car.
My Grandma's old Escort Wagon actually had a difference you can feel going up hills.
My Dakota has a much larger, much more torquey engine, I don't notice any difference. (the aerodymanics aren't too hot anyways)
My dad's truck probably can't even concievably measure it at any RPM/load. (Cummins diesel), the aerodynamics of a brick are better than the way his truck is setup.
My Grandma's old Escort Wagon actually had a difference you can feel going up hills.
My Dakota has a much larger, much more torquey engine, I don't notice any difference. (the aerodymanics aren't too hot anyways)
My dad's truck probably can't even concievably measure it at any RPM/load. (Cummins diesel), the aerodynamics of a brick are better than the way his truck is setup.
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