A heat pump type refrigeration system for air conditioners. The system has a heat pump type refrigeration circuit including a compressor the suction side and discharge side of which are switchably connected to an indoor heat exchanger and an outdoor heat exchanger through a four-way valve. The other sides of the heat exchangers are connected to each other through a first pressure reducer, gas-liquid separator and a second pressure reducer. A refrigerant tank is disposed in a pipe interconnecting the four-way valve and the indoor heat exchanger, in a heat exchanging relation to the pipe. The gas-liquid separator is connected at its upper portion to the refrigerant tank. The heat pump type refrigerant circuit confines a bi-component refrigerant consisting of two refrigerants of different boiling temperatures.