On our 2011 Sunseeker 3100, the heat pump will go into defrost mode when the outside temperature drops below 40 F. It runs in defrost for a certain number of minutes, putting out no heat, then runs putting out heat for a certain number of minutes. The outside temperature sensor is mounted on the unit. Below 30 F our Dometic thermostat stops the heat pump and runs the furnace, even if the thermostat is set for heat pump. Your thermostat may work differently.
2011 Sunseeker 3100
1997 Pathfinder Toad