OK we all know that running the ac can take away from your milage. But does it matter if i have the fan on full or just set to 1 is there a difference? Or if the ac is on its on and nothing really matters.

I know this is a dumb question but i have always wondered this.:confused:

Technically, with only the fan on your load is only on the alternator instead of both the alt. and compressor. The higher you have your fan speed, the more power is needed to overcome the additional resistance from the alternator. So yes, there is a difference. Is it measurable in the course of a tank of fuel? I wouldn't think you would be able to calculate the differences unless you were on a dyno, conditions were exactly the same, and the same quality fuel used.

Electrical usage isn't really measurable fuel wise. The thing is, your clutch fan is on whenever the a/c is, so that is the main thing that uses more fuel.

If the AC is on, it is pretty much on. As stated above, the fan speed will also add some resistance because of the additional power needed from the alternator, but how much is hard to say.

Jon

If the AC is on, it is pretty much on. As stated above, the fan speed will also add some resistance because of the additional power needed from the alternator, but how much is hard to say.

Jon

Thanks thats what i wanted to know.

forget where this study was done but it was basically windows down and no AC used more fuel than with windows up and AC on, BTW higher fan speeds equal more amp draw=loss of HP/milage but not something that could be measured or amount to anything....

The fan clutch does not lock up and run the fan when the A/C is on all the time. The only time the clutch fan is locked up is when the air running across the bimetal piece on the clutch fan changes and locks the clutch. Normally that is a hot day when the engine is idling. The A/C creates more heat across that fan clutch and will cause it to lock more when idling that if it were not on. But once you get moving down the road, the fan is not locked in. Otherwise you would hear an enormous roar from the engine, and you would be getting about 6 mpg with it.
Actually, no fan is not needed when you are running down the higway. It is only when you stop and are idling.

Also your A/C is on whenever you have the defrost mode selected, whether its is only defrost or defrost and floor as well. So remember to switch it to vent if you don't need the defrost.