Patent ID: 8393170

Claim:
A capacity control system for a variable capacity compressor whose capacity varies with change in control pressure, the variable capacity compressor being inserted, together with a heat radiator, an expansion device and an evaporator, in a circulation path for circulating a refrigerant, to constitute a refrigeration cycle of an air conditioning system, a pressure of the refrigerant at any portion in a discharge pressure region of the refrigeration cycle being used as a discharge pressure, and a pressure of the refrigerant at any portion in a suction pressure region of the refrigeration cycle being used as a suction pressure, the capacity control system comprising: a capacity control valve capable of adjusting the capacity of the variable capacity compressor by varying the control pressure; external information detection means for detecting one or more items of external information related to the refrigeration cycle; and target suction pressure setting means for setting, based on the external information detected by the external information detection means, a target suction pressure for controlling the pressure in the suction pressure region as a control target; wherein the control pressure is varied to adjust the refrigerant discharge capacity of the variable capacity compressor such that the pressure in the suction pressure region becomes equal to the target suction pressure; suction pressure estimation means for estimating, based on the external information detected by the external information detection means, a pressure that is estimated to prevail in the suction pressure region if the variable capacity compressor is operated with a maximum discharge capacity; and discharge capacity determination means for determining, based on the estimated pressure of the suction pressure region estimated by the suction pressure estimation means and the target suction pressure set by the target suction pressure setting means, whether the variable capacity compressor is operating with the maximum discharge capacity or with a controlled discharge capacity.