Heat pump. The aux light comes on and stays on the whole time the compressor is running.Outdoor temp is between 45-55 deg. Checked outdoor fan unit and it is real cold, telling me that it is on the heat cycle.
Ron

Even an old HP should be able to produce enough heat at those temps. Can you confirm your aux heat is in fact on? What type of aux heat is it: furnace or heat strips? What happens when you switch the tstat to EM/Aux heat only; does the HP still run?