Fan trouble '85 Prelude

Trying to find out why cooling fan won't come on after normal operating temp. is reached. When the a/c is turned on, both fans will turn on.Is the fan controled by a temp. sensor that may be out,or am I missing something? Already checked relays and fuses.Hope someone can help.Thanks

The fan will only come on after it gets a little higher than normal, and when it cools back down, the fan turns off.