I went on a 400 mile trip today.
First 204 miles I used approx 5.5 gallons = 37 mpg next 196 miles, 4.0 gallons = 49 mpg
This only difference between these two trips is that I used my AC for the first 200 miles.
I had no idea the AC affected the gas mileage so dramatically.
This makes sense, if you look at the power levels required at steady speed (which is what these numbers would indicate).
At a steady speed, especially one below 50-60 mph where wind resistance is much lower, much less power is required to keep the car moving than to accelerate or climb grades. The power consumption of the a/c compressor remains fairly constant. As the ratio of power between locomotion and compressor drops--as the compressor takes a bigger proportion of the engine's output--the relative effect of shutting of the A/C becomes larger.
In more than 65,000 miles of driving my '00 Accord, I have seen little difference in gas mileage whether or not I was using A/C. The difference might be more marked in the Civic, with a smaller engine, but it's unlikely you'll see a disparity of almost a third over the long run.
IMO.
Paul
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