The emergency heat keeps activating and the unit runs constant while the emergency heat is activated. The unit while not exceed the temperature setting on the thermostat. The unit seems to be operating okay, but it does not cycle on and off. When I change the thermostat from say 68 to 70 the temperature will change on the thermostat and by feeling in the house to 70, but the emergency heat will activate and the unit will not go above 70 or cycle off. Any suggestions? My unit is a Trane installed in 1999.