1997 galant 2.4 fan inop

[foxygoliath]

I have a 2.4 liter galant found car was overheating changed the thermostat still over heats changed the temp sensor behind thermostat housing still the same thing. I notice the temp gauge reads the same on the dash it is in the middle and doesnt move. I had the car checked for codes no codes stored in pcm. I noticed the fans only comes on when the ac is on. The fan doesnt turn on unless the ac is on. What could this be thanks in advance for your help.