My car doesn't have A/C. But when I'm in a car that does, I usually only turn it on to take the edge off and then go with the windows down, just because getting out of a cold car and into the heat, sucks more than being ready for it.

If I'm going to be in the car for 25+ mins, AC for longer. But less than that and I'm just going to be right back out in the heat again, it's more annoying to go from nice and cold to balls hot. Than it is to just get a warm breeze the whole ride.