I have Trane xl1800 heat pump with a trane 5 ton air handler. The system seems to cool fine but when I call for heat it is the luck of the draw if it heats or blows luke warm/cool air. The outside fan is running-it is not stuck in defrost, the emergency heat works when I call it on. If the system has been off awhile or if I toggle back and forth between cool and heat it will sometime work. The only options I can find is either a short or the reversing valve is getting stuck. Any input/help on what I should look for would be appreciated. I have not check voltage at t-stat or condensor yet or tested the defrost board.