from what i can tell off of the wiring diagram. the ac does turn on the radiator fan, so that is normal. if you are positive of no leaks. try replacing the radiator fan switch. its on the thermostat housing. that is the only other thing in the circuit that has an affect on when the fan comes on.

fyi- i had a civic in this morning with an over heat problem. fan wasnt coming on. fan blew the 20amp fuse. but you said theyre all good so i beleive you