Actually, AC can impact FE more or less than driving with cracked/open windows. It depends on how much AC, how much open windows and how fast you are driving. Let me know when you run this study - I may do it when it gets into the 80s in Ohio.

Peace.

Absolutely! My point though is that at city speeds, this doesn't cause as much drag as the AC does. I have no idea how much of an impact opening the windows DOES have though since my mileage is stratospheric in the summer, even with the windows down (and I'm not willing to try driving with the windows up).

Luckily, I only NEED AC about 1 week of the year since our environment is so dry so I can get away with out it (although I still need soap....).

Commuter car, grocery getter, and summer road tripper--average 10k miles per year.


Winter road trips and ski trips, bad weather commuter and my wife's "daily" driver--expected average 4k miles per year.

Actually folks, Harold has a very good point here, one that I should emphasize more often. (Thanks Harold).

The IPU derives its effective cooling from the passenger cabin and it is in out best interest to give it some thermal advantage in doing its job particularly during the warmer days. The effects of a hot pack, MCM and to a lesser extent, the DC-DC can be felt in ways that totally dwarf the negatives of operating the AC. Those of you you have driven your HCH-II through a couple of summers know this quite well.

When it comes right down to it, it pays in more ways than one to do things wisely and with forethought.
So, using the AC moderately actually does some good. Using it strategically and wisely is even better not only for the components I referenced but also for yourself and your FE.

Cheers;

MSantos

That mythbuster test was done at 45 mph if you check the tape. Windows down is better at speeds up to about 55-60mph. If your cruising down the Interstate at 75mph, it will be better to use a/c if you have to than rolling down the windows going that speed.

No offense to mythbusters, but I would test it out on my own HCH2. Probably wont do the 75mph test though, I seldom break 60mph

Since we got the hot weather, our mileage has droppped about 10 MPG. However, we refuse to sacrifice comfort for mileage!

Another factor, as some have touched on, should be on how cool you want it. If you set our AC at 60 then the compressor will run almost continuously, if you set it at say 75 it should cycle on and off to maintain the temp. I would even go further and cycle it up and down as my personal comfort increased or decreased. It's just another thing to be hyper aware of as you hypermilers go about your driving. It works for me.

I usually keep my A/C at 70 and AUTO, when I use it. I found that with the tinted windows and a heatshield visor (when the vehicle is parked) that unless the temps get into the 80s, I'm fine with the windows up and no A/C. My mileage seems negligibly impacted by the use of the A/C, perhaps 2-3 MPG. Comfort is certainly worth that price, especially since MPG is in the mid 50s.

1978 Plymouth Horizon - 165,527 miles, still the longest lasting
1985 Dodge Daytona - 62,500 miles and the transmission gave out
1991 Mazda Protoge - A very good car
1997 Ford Contour - This one saved my life in a driver side impact accident
2000 Pontiac Grand Am - I have a bulls eye painted somewhere, this one was rear-ended
2004 Civic Hybrid - My first Honda, My first Hybrid, ran 88,300 miles before the tax rebates came calling
2007 Civic Hybrid - Going strong and a joy to drive
___________________________________________

194 mile round trip today, at 90deg F, avg speed 69 mph with 3 passengers, trunk full and A/C set at 76 AUTO gave me 50.2 mpg.

When my wife and kids are in the car, I have to use the A/C. I keep it at 75 and shut it off whenever I'm going up hill. It takes more effort, but I can nearly get 60 mpgs.

When I'm alone, I crack the driver's window and the rear passenger's window about 2 inches. I can easily get high 60's, low 70's in mpgs and still feel comfortable with that set up.