My 4-year old trane 14 seer heat pump won't turn on. Thermostat works and the unit clicks when I set the thermostat, but the unit won't kick on. What could be the problem?

Make sure you have power to the outdoor unit, check for any tripped breakers.

Probably not breakers but the, limit switch , bad . Or might need b cleaned they are two wires connecting to it doesn't matter how you put back on real cheap easy fix

Oh forgot , if that don't work check code on computer . Make sure your heat echange pipes not clogged I have same unit and that's my problem