Hi. I have a big problem that is killing me. I have a central Heat and AC unit that works well, but the fan won't seem to turn off. The AC and Heat works well, but the fan just keeps on running. I was gone for 3 months for ARMY business and my wife did not know that this was not working right, so I had to pay a 360 dollar electric bill. I replaced the thermostat and it still seems to keep running. Can someone help me?? I hope it's a cheap fix. Thanks all!

Art