I have a question concerning a car's air conditioning and how it affects gas consumption.

It's no secret that running the AC in a car reduces gas mileage but do different settings of temperature or fan speed increase or decrease fuel consumption?

For example, if the AC is on, does having the fan on full blast use more gas than having the fan set to low?

Likewise with temperature. If the AC is on, would setting the temperature to half way or even hot use less gas than full cold?

And I suppose I'll throw recirculation in there as well. does turning this on change consumption?

I'm on one of those fuel economy kicks with my car and can't figure this one out. Any insight would be appreciated.

 

These will affect your gas mileage negatively:

Running electronics (but not much)
Temperature set colder
Using non-recirculating setting

 

The compressor on the car or vehicle cycles on and off through a clutch on the belt drive, when the drive belt is turning the pulley on the a/c when it is cycled on, it puts a little more strain on the entire belt drive of the vehicle. Thus making is harder for the engine to turn the belt drive, however this isn't a big difference it is a minuet change. This cycling of the a/c compressor happens when the a/c is turned on, it cycles more the higher the setting and stronger it blows. But you are more likely to get better gas mileage by changing your driving habits, and by leaving your vehicle in Over-Drive more of the time than running your ac less. It will make a difference maybe by 1-2 MPG.. MAYBE. Switching to a little higher octane gas, keeping a clean fuel system, as well as getting the proper servicing and the correct intervals, and driving more conservatively will help you more than running your ac less. I'd sacrifice that little difference for being comfortable.

 

i saw an episode of mythbusters the other day where they were figureing out if tailgaiting someone will save you gas mileage from less air resistence like drafting in a nascar race for instince and wether or not running the a/c or haveing windows open gets better gas mileage, conclusions were that tailgateing about 10 feet back or so from the car in front will increase your gas mileage a little but gettin to close means your usually on and off the throttle more so you loose gas mileage, and windows open actually looses more gas mileage from the air drag factor than running windows closed with ac on, and haveing the fan speed set high or low doesnt make enough of a difference to matter since the fan in the car is not controlled by the motor directly its just an electrical pull from the battery

 

Yeah it's over 50mph or something and the drag from a window down is more than running AC.

 

Also keep in mind, most cars whenever the defrost is used, will cycle the ac compressor as well. So when your using your heat in the winter, it actually kicks on the ac compressor and charges the system. They do this to keep the system operating during a time period when nobody would use the ac. It keeps the pump from seizing up while keeping the system lubed.

You can also run your tires at max air pressure. Low air in the tires will sacrifice a mpg gallon or two if under inflated by only a few pounds.

I've also heard some mpg can be had by keeping the car clean. Air flows over a clean body easier than a dirty one.

Also, a little off topic, but what I found interesting with mythbusters on mpg was when they did the truck tailgate up or down. They found that the tailgate up was actually better for mpg. Something to the affect of the tailgate creating a swirling of wind, that actually made the air move faster over the back end of the truck and was less resistant that the tailgate down.

As already said, the different fan settings should have no effect on mpg.

As bubba said, running your car in overdrive can help. But I would add that only if your in a situation where overdrive is required. If your in too tall of gear and out of the zone where your car makes power, you will get worse gas mileage, especially if your in hilly areas or speeds of 55 or less. Personally, I usually only use overdrive on the freeway. But I live in a very hilly area and overdrive just doesn't work too well here.