I put a fan in our coop too. At first they were scarred to death of it, but once they figured it was sooo much cooler in front of it, they all bunch up around it.
I have a fan in mine also. I put a mister in front of it to cool off the air before blowing it in the coop. The hens play in the water (as much as chickens can "play") and scratch around in the mud. It helps a little, but I can't wait for fall either.