A ductless system consists of 2 parts, the outdoor compressor/condenser and the indoor evaporator/blower combination unit or indoor unit. The 2 units are
connected via refrigerant lines that cool the air in air conditioning mode, or heat the air in heating mode (for heatpumps only). In the AC (air conditioning)
mode if the thermostat calls for cooling the compressor sends the refrigerant to the condenser as a hot and high pressure gas. In the condenser it
cools and turns into a liquid and it then travels to the evaporator / blower unit inside the home. As the liquid travels through the evaporator, the
blower is operating and blowing the room air over the evaporator coil which in turn is cooling the air. The refrigerant goes back into the compressor
as a liquid and is then converted back into a hot, high pressure gas and starts the cycle again.
In the heating mode, the heat pump extracts heat from the outside air and sends it into the evaporator/blower unit via the refrigerant lines. Even at relatively cold temperatures the heat pump can still extract heat from the outside air. However when the temperature drops below the capability of the heat pump to provide heat, you would have to run your primary heat source such as your boiler or base board heaters.