First about your heat pump system. Basically a heat pump is a
compressor. When in the "COOL" mode, it will remove heat from your
home and transfer the heat to the outside. In the "HEAT" mode, it will
remove heat from the outside and transfer to the inside. When the
outside air temperature drops the amount of heat extracted from the
compressor is no longer suffiicient to heat the house and electric heat
is required as supplement heat. Also, the heat pump manufacturer will
have specifications as to when the heat pump should be turned off below
a certain outside air temperature.

The last post was correct about the heat pump in the way that it
functions. However I feel that Minasota Is way to cold for a heat pump
application. When it gets as cold outside as it does there the heat
pump wont work and you will have to rely on your electric back up
heat.It wont damage your furnace to run the Back up heat strips but
will cost more to run. When the outdoor unit gets a covering of ice on
it it should go into a defrost mode and run as a normal A/C unit to
melt off the ice. You will see steam and hear hissing and cracking as
the ice melts. This is normal and dont be worried. If it never defrost
then there is a problem with that part of the system and it should be
checked by a HVAC service tech. Hope some of this helped. Steve. Arctic
A/C Services. Fl.