At around 38 and below degrees, the outside unit will heavily frost up or ice up and run continually like that for an extended period of time. Say around 1 or 2 hours before defrost mode kicks in. Its doesn't seem to do a complete job of defrosting all the time either. It will run almost continually most of night blowing out cool or room temperature air, barely keeping a degree below set temp. Aux. heat has never kicked in during defrost or otherwise. But it will, if I crank up set temp a couple degrees above original. Is there a problem with it, running constantly all night like that?