A high efficiency air conditioning system combining a desiccant assisted air conditioner with a heat pump device is disclosed. The heat pump device has a desorber for separating a refrigerant vapor from an absorption fluid; a compressor for compressing the refrigerant vapor; an absorber for absorbing the refrigerant vapor in the absorption fluid; an absorption fluid passage for circulating the absorption fluid between the absorber and the desorber; a refrigerant compression passage for transporting the refrigerant vapor produced in the desorber to the absorber by way of the compressor; and a heat medium passage means for drawing out heat of absorption and heat of desorption generated in the absorber and/or the desorber. Facilities are provided for storing refrigerant and absorption fluid during various modes of system operation and appropriate valving is provided for operating the system in various modes to increase the economic efficiency of system utilization.