pretty sure only one fan will come on with the A/C unless the engine coolant temp is over 207 degrees...then both fans will come on
if you have auto climate control it blow cool until it drops to say 65 degrees, but then it should stop....not start blowing warm air.
Do you have the temp control set to the coolest temp or to 85??? Set it all the way to cool and see if it just blows cool air only