[E90330iS]

Hello guys! On really hot days I find that having AC at 60 degrees 1 bar has the same effect as 70 degrees with 2 bars, but which one is more fuel efficient? Which one uses more power from the energy? I am just wondering on how the A/C works!

[rawpower]

i wasnt aware that 10degree change would make a really noticeable fuel efficiency

[Potty_Pants]

(not being mean... just messed up)

does it really matter ? or is it just a hmmm wonder which is better question ?

its like me complaining to my buddy about getting 15mpg... his response WTF do you care ? you drive 5k a year you fill up once every 3 weeks.

so if it saves you 1/5 of a gallon over a tankfull you/we've bought a car where fuel efficiency wasnt top priority.

but to answer your question... i cant. im sorry.

ppp

[iatacs19]

Well think about it, it's common sense. If you set it @ 60F then the A/C will cycle more to maintain the 60F temperature inside the cabin in contrast to 70F. So, 70F will be more fuel efficient since the A/C compressor has to be used less than if it were set at 60F.

[LEDZEP]

I hope you're not one of those people that think the car will cool faster if you set the temperature lower...

[tibook]

I always thought the compressor either runs, or it doesn't, the only thing that changes is the interior fan speed...you save gas by turning it off.

[kuthair]

Originally Posted by iatacs19

Well think about it, it's common sense. If you set it @ 60F then the A/C will cycle more to maintain the 60F temperature inside the cabin in contrast to 70F. So, 70F will be more fuel efficient since the A/C compressor has to be used less than if it were set at 60F.

+1... fan speed uses too little power to make a difference. AC compressor cycling will be the biggest hit.

I wouldn't worry about it all that much tho...

Mythbusters actually had an episode comparing using the A/C vs keeping windows open, but I dont remember the results.

[Potty_Pants]

IMO the mythbuster's episode was seriously flawed.

they had to limit their speed to 45 due to potential tire blow out.
its been mentioned many times before around 45 and under their is less drag on the car and this would result in the recommendation they reached. "Keep the windows down and the AC off". While this may work at 45 or so this doesnt fly at 55-60-75-80 which is where the original tests were performend and they (non mythbuster's) found it more efficient to have the AC on.

ppp

[KL2DC]

aerodynamics for each car is different, I think AAA did a similar study about having the windows down causing unwanted aerodynamic drag. In the end economical use of the a/c is a better alternative.

[Carnage]

Just set it to whatever temp makes you comfortable and don't worry about it. It's not like you're going to lose 10 MPG by running the A/C alot.

[Revlis]

ROTFL....

OK, Seriously though the MAX setting? That has to use more fuel cause it damn near removed my hat the other day... That's a tool we must learn to use responsibly.

Bottom line IMHO, Why worry about fuel mileage? Seriously, are you going to STOP driving? No, are you going to swelter in the heat to save gas? No, so why spend one more second discussing the price of gas or whether or not this or that will get me an extra 4-5 MPG. Just doesn't matter, chances are you are not going to change your driving habits, you're not going to start riding the bus, and you're not driving a freaking Prius so obviously you are really NOT that worried about fuel mileage.

Unless we are just discussing it as small talk, kind of like the weather. In which case I'd have to agree with the others and it would make sense that your A/C running at and maintaining 60 deg would be working harder, placing a higher load on the engine, thus using a thimble or two more fuel than running it at 70deg.

[GS833]

The A/C compressor is either going or not, it has nothing to do with the speed of the fan. If you see the little light on the A/C it means it's running no matter what your fan setting is. Like someone said, the fan doesn't use enough power to make a difference in fuel economy. Besides, new A/C compressors don't suck up enough power as they used to...

[BMW_drei]

Originally Posted by KL2DC

aerodynamics for each car is different, I think AAA did a similar study about having the windows down causing unwanted aerodynamic drag. In the end economical use of the a/c is a better alternative.

+1
Aero drag increases with the square of speed (remembering back a ways...) -- with the windows open, you're driving a parachute. At low speeds it doesn't matter, on the highway it can be big.

[tibook]

Originally Posted by GS833

The A/C compressor is either going or not, it has nothing to do with the speed of the fan. If you see the little light on the A/C it means it's running no matter what your fan setting is. Like someone said, the fan doesn't use enough power to make a difference in fuel economy. Besides, new A/C compressors don't suck up enough power as they used to...

Also, the MAX button recirculates the air, and gives you the most fan speed, thats all. It doesn't turn the compressor into super-overdrive.

[kuthair]

Originally Posted by GS833

The A/C compressor is either going or not, it has nothing to do with the speed of the fan. If you see the little light on the A/C it means it's running no matter what your fan setting is. Like someone said, the fan doesn't use enough power to make a difference in fuel economy. Besides, new A/C compressors don't suck up enough power as they used to...

Yes, but set at 60 vs 70 the compressor turns on more often. Just because the A/C light is on, doesn't mean the compressor is on. It just means it will use the compressor when needed. This is my understanding anyway.