@Konneh ,
Your heat pump uses auxiliary heat when necessary to assist on those very, very cold nights. Additionally the heat pump will build up ice on the outdoor coil. The heat pump defrost control board detects the ice buildup and when needed, it initiates a defrost cycle. During the defrost cycle, the reversing is switched to bring warm air from inside the house to speed up ice meting. This means it is temporarily acting like an air conditioner. So, the defrost board will activate Auxiliary heat to ensure the air cycling over the coil is warm and not cold. By design, the thermostat does not allow the homeowner to control the auxiliary heat. What is possible, is that a heat pump capable thermostat can provide an Emergency Heat function. This Emergency gives the homeowner the ability to activate the electric heat strips on the case when the outdoor Heat Pump fails and needs repairs. In this way the homeowner has some heat until the HVAC Technician can arrive the fix the heat pump.
To get thermostat support for both auxiliary and emergency heat, you must use a Nest Learning Thermostat 3rd Generation.
AC Cooling Wizard
NestPro, Google Pro, Mechanical Engineer and HVAC service company owner.
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