Abstract: An air conditioner is selectively operable in a main heating mode, a cooling mode and an auxiliary heating mode. In the main heating and cooling modes, refrigerant is circulated through a main line which includes a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger. In the auxiliary heating mode, the compressor is not activated, and the refrigerant is circulated through an auxiliary line having opposite ends connected by valves to the main line at opposite sides of the indoor heat exchanger. A pump and heater are disposed in the auxiliary line so that in the auxiliary heating mode, refrigerant is circulated by the pump through the heater and the indoor heat exchanger and back to the pump.