I recently had a new Trane XL15i heat pump (4TWX5036) with variable speed air handler installed replacing an older Bryant system. The system seems to be a big improvement over what I had at least when the temperature is above 40 deg outside. My question is about how the defrost on demand should work and how best to verify it is working. The overnight setting is 60 deg and the daytime setting is 68 deg. I usually adjust the set point around 5 am and when the outside air temp is below 40 deg the unit frosts up quickly and the heat output goes way down taking an hour to raise the inside temp 1 deg. Heavy frost is a solid blanket of frost/ice on the coil fins from top to bottom of the inlet vents. It is clear that very little airflow is reaching the coils at this level of frost. After an hour or more I usually lower the set point and wait for the outside air temp to increase when the sun comes up which is obviously not a solution. The installation contractor has come out and tested the defrost board and the coil temperature sensor and both checked out and they feel everything is ok. I want to be able to provide better input for the contractor so they can correct this problem. It is difficult for them to be here at 5 am to witness the level of frost. If I could monitor the actual coil outlet temp and outside ambient temp and if I knew the logic used to activate the defrost then I could provide the contractor with the information they would need to troubleshoot the issue.