Quote:
Originally Posted by MetroMPG
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That 6% hit due to an air conditioner sounds reasonable to me.
I just got off a 400-mile trip in typical-for-around-here 95F weather with the air conditioner keeping me cool in my Mazda3. As I noted above, it always seemed the variables on the highway kept me from seeing a difference on the Scangauge comparing the mileage with the compressor on vs off. However, today the conditions on a very flat section of road let me see that difference for the first time on the gauge. I cycled the AC compressor on/off, and indeed the instantaneous mileage screen showed a several MPG hit with the compressor on vs off.
Usually, variations in the road or traffic or wind made too much "noise" for me reliably to see it on the gauge. Not so today. The differential showed up there.
Today, without the intervening effects of any noticeable wind, with the AC running I got some of the best mileage for my car, 49.2mpg. The only "hypermiling" I do on the highway is speed control, and today I benefited from being able to find a truck that was running about 55mph on a 70mph Interstate over a 50-mile stretch. So, I stuck behind that truck at about a four- or five-second elapsed-time distance for about 50 miles, which let me benefit from the bit of extra mileage without attracting the hatred of those who were passing us at a 70 - 80 MPH clip. Without the truck for them to blame, I would have been running much faster for sure.
So, I know the air conditioner cost me some MPGs, and the Scangauge confirmed that today. I just don't know how many MPGs I lose, as asked by the OP. Because I live in a tropicalesque climate, the air conditioner runs the vast majority of time, and my Fuelly records don't show much difference in mileage winter-or-summer that could be attributed to the air conditioner; at least as far as I can tell.