Community Forums

grassy · 08-22-2016, 06:14 PM

Odd question.

I was told that running the a/c will cost a couple mpgs ...I have also been told that mileage really doesn't vary when hauling unless you go to extremes..

I am happy with my mpg and I am not turning off the a/c... but these two statements contradict each other..and I am a curious type..

I have asked this question in other areas and haven't heard a good explanation.

If weight pulling really doesn't affect mpg then how is a/c compressor drag a factor ?

Bigd9 · 08-22-2016, 06:43 PM

The question about air using air conditioner versus fuel mileage has been around for the last 60 years! It never seems to die out. But to try and answer your question, I have never seen a credible study where it has been proven to reduce the mileage one iota. Sure many people just know it does, but actual proof is lacking. Sure it cost fuel to drive that air conditioner compressor, but then the windows will be shut increasing the aerodynamics of the vehicle. Some say that their mpg actually increases with air conditioner use.

Fuel mileage is derived by many factors. With my current 330 CAT C7 engine I do not notice any difference in MPG towing vs not towing, probably because I'm not calculating the mpg to enough decimal places. In my previous Cummins 275 HP coach, I did see a 0.5 mpg difference.

Rook · 08-22-2016, 06:47 PM

Hmmm....I think you already know the answer to your question. Using common horse sense, I think they both effect MPG in a small way......but not much under normal circumstances.....and not enough to be concerned about. Rook

1ciderdog · 08-23-2016, 05:44 PM

I've put over 100K on this RV and tracked every gallon of fuel and mileage, with notes such as ran AC all day or ran generator to run AC, mountains, cross winds, etc. Mileage always varies and I think mostly do to terrain and/or head/cross winds. Not the least bit scientific but that's the way it seems to me.

Skip426 · 08-25-2016, 06:26 PM

A/C use , what's your comfort worth ?
Automotive a/c compressor , draws about 11 HP when cycling , I can feel it cut in in my mini van , can't in the coach .

Headwind and a heavy foot will do more to MPG that anything else .

Just in case you don't have it , here's what Cat has to say.

Bigd9 · 08-26-2016, 04:40 AM

Quote:

Originally Posted by Skip426

A/C use , what's your comfort worth ?
Automotive a/c compressor , draws about 11 HP when cycling , I can feel it cut in in my mini van , can't in the coach .

Headwind and a heavy foot will do more to MPG that anything else .

Just in case you don't have it , here's what Cat has to say.

Hi Skip, thanks for posting that attachment. I found it interesting seeing all the things that affect fuel mileage. Most were common sense but a few were a surprise. Like winter time fuel and the fact new tires are worse on fuel economy than tires 50% worn. A real surprise was the fact new tires are worse on fuel economy than idling an engine 10% of the time! Gee and to think I just got rid of 6 tires that were at their peak of their fuel economy just because they were 11 years old!

jtmccarthy · 08-29-2016, 01:13 AM

Quote:

Originally Posted by grassy

Odd question.

I was told that running the a/c will cost a couple mpgs ...I have also been told that mileage really doesn't vary when hauling unless you go to extremes..

I am happy with my mpg and I am not turning off the a/c... but these two statements contradict each other..and I am a curious type..

I have asked this question in other areas and haven't heard a good explanation.

If weight pulling really doesn't affect mpg then how is a/c compressor drag a factor ?

If traveling in Nebraska, then weight pulling costs about 1mpg. In Colorado mountains, 3-4 PMG. Flat requires only rolling friction. Hills cost lifting, not cheap. AC is constant drag when the compressor clutch is engaged. First on, pulls more HP than when compressor is up to speed (very short time, 200ms), but either case requires HP. Pulling and AC are not free....what is?