Electronic Climate Control Question

I have a 98 taurus se and have always wondered something about the electronic climate control. I always just leave it on auto. However, one day i was curious if i hit the max a/c button would the car cool down faster. So i did but i didn't hear any difference in the fan noise. On my other taurus that i had (and any other car i've used max a/c) when max is turned on, there's more noise from the intake fan turning on. Does auto automatically use max a/c or what? Also, it seems that my outside temperature sensor is now off by 5 degrees or so. I know it's on the dash up by the windshield. Is it possible that it's just got dirt or some armor all on it and that's messing up the reading?