I have a Trane heatpump, and at night it will not heat up to the set temp of 72 degrees. For example it might be 40 degrees outside, and I'll have it set to 72, and this morning when I woke, it was 66 degrees in the house. And when I turn the thermostat to the off position, it continues to run and blow cold air, for at least 30-45 minutes before shutting off. What could be the problem and would should I do? Thank you!