how do you figure? unless you have a lawnmower engine under the hood the added resistance on your pulley from the compressor should be minimal to say the least. and you should be revving to 2k rpm (or whatever the org. allows) when metering anyways...
and i doubt the cold air from your a/c will be that much denser to affect your score at all... i admit i have tried it before but i had nothing to base the score off of...