You won't be able to move anywhere near the amount of BTUs your car's AC does.
I'd recommend tinting your windows instead.
http://www.gisdistributing.com/V_Koo...e_Poducts.html
That stuff blocks out most of the heat while letting visible light through so you won't get hassled by the cops. I put limo tint on the back side windows of my car and I'm going to do the back in limo tint too, but on the front windows, I'm going to use V-Kool. Sunlight produces about 1KW of heat per square meter, which is about the size of most rear windows. Every watt of energy you stop at the windows is probably 4 that you don't have to rob from the crank to maintain the same comfort level. You might even be able to get away with just the blower.