I run window air conditioners. Every year I go through this when it is in the 90's outside. I live in Detroit, Mi. The flies hang out in the sunny windows. I don't think they like the cool air inside and are trying to get back out. I think they get in through the air conditioners. Every few hours I open the windows and shoe them back outside. I let out at least 60 at a time. Any clue about this situation?

Likely they are actually breeding inside the a/c units if you have that many coming in. You could try puffing some roach powder into the units(not the air handling part, the part that sticks outside where the compressor and drip pan are) to see if that will lessen the problem.