Air Conditioning - Heating and Cooling

When cooling, the air conditioner operation is similar to that of the home refrigerator.

The indoor air circulating fan draws air into the conditioner through an air filter and over a cold coil (containing refrigerant) cooling the air before it is circulated back into the room.  
In addition to being cooled, the air is dehumidified when moisture in the air condenses on the cold coil. This condensate is caught in a drip tray and drained away.   
  

The refrigerant carries the heat absorbed by the cooling coil (evaporator) to the outdoor heating coil (condenser) via the compressor and expansion and reversing valves. The outdoor air circulating fan forces air over the hot condenser coils, cooling the refrigerant.

When switched to the heating cycle a  valve simply reserves the flow of refrigerant,  so that the heat is gained by the outdoor coil  and used to heat the inside air. The operation  of the heat pump is possible because even on  very cold days usable heat can be extracted  from the outside air.