[Merlyn2220]

I ran another tank, trying to use the A/C about the same amount as the last one. MPG ended up at 13.92, compared to 13.79 the last week. This is substantially lower than before the 12 degree mod @ 14.31/14.44 for 2 ~32 gallon tankfuls. So now that I'm fairly confident of ~13.85mpg with the mod and A/C, I'm running the next tank without A/C. Hopefully that'll tell me if the aero mod is a net negative or positive.

I hadn't thought about replacing the A/C system, but I don't really use it all that much. That's either a good argument for not bothering to fix it, or that replacing it with a smaller unit would be perfectly acceptable. Conventional wisdom is that the AC compressor uses around 8hp, and is about the equivalent of a 1.5-2 ton system. At around 20,000BTU/hr that's an electric equivalent of 1500-2500 watts, or 2-3.3hp. I could probably get away with an effective A/C about 1/4 that size, since I rarely put it over "low" on the fan except in the middle of summer. Even at 100% efficiency, an electric one would need to be good for 375-625 watts, or up to ~45A. The 12V car compressors are good for around 300-400BTU/hr, which is 1/50th as big as the stock car system. Unless I'm missing something, I don't see how this could work.