[quote[So the test was - OFF or AC/MAX.
Maybe there's a more normal setting that results in less MPG dropoff? I think many people do NOT leave their AC on MAX all the time. Although in hot climates, like mine, it is more often than I'd like to admit![/quote]
The problem with setting it to a more "normal" level is that there is no easy way to control that experimentally. Of course, the problem with running it at max all the time is that it does not take into account how powerful the different air-conditioners are. A vehicle with a small, underpowered AC on "max" would not do as much cooling as a more powerful unit, but that does not make it more efficient just because it affects MPG less...

However, showing max AC does show a good "worst case scenario" for the sake of reference. To accurately gauge a "normal" ac use, they'd need to determine the gas consumption to maintain vehicle temperature X degrees below ambient temperature, quite an undertaking.

 

I'm sure you can just interpolate between the AC-off and max AC figures to come up with a reasonable estimate.