Save gas by not running A/C with defrost

[stran]

So can you control when to run A/C instead of running it all the time. Here's what I do when it's cold at night (and hence near the dew point which means things fog easily) or when it's raining:

To prevent fog from forming - defogger mode with cold air. I also do this when I start my car. By not having the A/C on, it's not as cold in the cabin and I don't need to poach heat from the engine so it warms up faster. Cold engine = bad bad gas mileage.
A little fog - defogger mode with warm/hot air. No A/C = no compressor = half the gas consumption at idling (according to SG II).
Heavy fog - haven't had time to see if I even need to run A/C to clear the windshield, but if needed, I will run it in spurts instead of running it all the time.

Also, running the rear defogger has almost no impact on gas consumption - it uses less gas than turning on the headlamps.