Icing

Ready for the flame as I am only a homeowner but..... Recently moved into a new to us home which has a Carrier heatpump installed. This is the first home we have had that uses a heatpump so don't really understand them. Now to the question. Home is in coastal North Carolina and weather has just hit the high humidity, barely freezing point. Noticed this morning that outside unit is icing up. Icing starts with three bands spaced equally apart from the bottom of the unit to the top and then fills in so entire unit is covered with a coat of heavy frost. Don't believe this is normal operation but before I call a "qualified technician" thought would run it by this group. Am not asking for a specific diagnosis but would like to have some idea of the causes to protect me from "unqualified technicians" when I make the call.