If your ac is calling for heat and it is instead blowing hot then it sounds like you have a heat pump, am I right? And it sounds like either your thermostat has failed or (more likely) possible the switching solenoid (can't remember the frigging term.. its where there's one pipe coming in and three coming out). You can check.this n yourself but if you don't know what your doing you're in for a bad time. Heat pumps when they fail default into heating mode. Have a tech come out and check. Probably an easy fix, but since there is high voltage involved i don't recommend you do it yourself.