What is the altitude of San Diego versus Ventura?

What were the prevailing winds?

My point is that you can't get an accurate comparison by looking at only one leg of a round trip. You'd have to repeat the entire trip under identical conditions to be able to isolate the one variable.

That's not to say that using AC has no effect on fuel consumption, of course it does. But there are so many variables in regular driving that it'd be very difficult to isolate just one. That's why the EPA test is synthetic, it allows them control of all the variables.