With an air-cooled packaged heat pump system all air moving fan, heating and refrigeration systems are contained in one weatherproof enclosure located outdoors. Ductwork is normally used to direct and distribute air from the unit to the interior of a building or home. Conventional air-cooled heat pumps utilize electricity to drive the compressor and condenser (outdoor) fan to produce both heating and cooling modes of operation. A supplementary electric resistance heat strip may also be employed on the unit to assist heating operation at lower ambient temperatures and to maintain warm air flow into a building or home when the heat pump enters "defrost" mode to de-ice the condenser (outdoor) coil. These systems range in sizes from 1½ - 20 nominal tons cooling capacity.