Turns out, you're a giga-savant whos brain works better than a trained physicist, who could tell you exactly how air conditioning is supposed to work but has never experimented with one empirically. See, air, much like water, flows in the direction of least resistance. Guess what happens to air when you pump it into a sealed room? Hot air, cold air: it doesn't matter... If you said something along the line of "it begins to push against itself until it finds an easier place to go," then you've got some mind! Just try it for yourself. shade your room with blinds, crack the window, maybe crack the doors open in other rooms. Make sure the other rooms have closed windows (remember, we're directing air at this point), and let the AC blast... Booya! Your friends were just getting on your case because their parents got on theirs, not because closing your window cools a room faster. Should you have all the windows open while running the AC? Heck no. Think of the ratio! how much air does your AC blast anyway? So, then, guess what you do when your room is finally nice and cold, and likely one of, if not the coolest room in the house? Yep. Close the window. It should take about 20 minutes!