Hello, I came home this pm and my heater was running nonstop. I have changed the thermostat, but the fan will not stop running. The only way to make it stop is to turn of the breaker outside. It is a AR36-1

When you say its running nonstop--- is it heating but the blower is on all the time?

It is heating and blowin all the time. I have tried to set it to cool, but it still blows hot air.

Did it do this before you replaced the thermostat? If so Is this a heat pump system?