I've noticed that the car burns a little more when I use the windheild defroster. Can anyone tell me if thats because the a/c compressor comes on even if its frigid outside? And if it does- can I disable the compressor somehow at least until spring?

the compressor does come on, but it doesn't 'cool' the air. it conditions the air, IE, it dehumidifies it, so that the air on the inside of the car loses some moisture, and doesn't fog up the windows as much. it's a nice little feature, one that's definitely worth 1 or 2 mpg, i think