A double-acting refrigerant compressor comprising a piston freely guided on two cylinder portions (41,42) arranged opposite to each other and being immobile relative to each other, said piston comprising a flow channel extending internally through the piston, each cylinder portion (41,42) and the piston comprising, along the flow channel, respectively at least one back-check valve (10,11,12), wherein the back-check valves (10,11,12) are arranged in such a manner that their flow directions are unidirectional, wherein the piston on an end side thereof comprises a low-pressure compression face adjacent to a compressible low-pressure working volume, and on the opposite side thereof comprises a high-pressure compression face adjacent to a compressible high-pressure working volume, said high-pressure compression face being smaller than the low-pressure compression face, wherein the compressible low-pressure working volume is formed between the low-pressure compression face, an inlet valve plate comprising a first back-check valve as an inlet valve, and a first cylinder portion, and wherein the compressible high-pressure working volume is formed between the high-pressure compression face, an outlet valve plate comprising a second back-check valve as an outlet valve, and a second cylinder portion, characterized in that that the piston comprises, between the low-pressure compression face and the high-pressure compression face, an auxiliary compression surface which together with the first cylinder portion forms an auxiliary volume that is designed, in case of a stroke movement of the piston caused by a drive force, to generate a restoring force acting against the drive force and thereby to assist in the control of the piston in that the auxiliary volume - can be brought into a first state in which the auxiliary volume is vented toward the ambience of the refrigerant compressor so that an atmospheric normal pressure is caused to prevail in the auxiliary volume, - can be brought into a second state in which the auxiliary volume, while being gas-tight and having a constant pre-pressure p0, is operative as a gas pressure spring, - can be brought into a third state in which the auxiliary volume is connected to an inlet line connected to a refrigerating system so that the pre-pressure in the auxiliary volume is equal to the working pressure in the refrigerating system, and - can be brought into a fourth state in which the auxiliary volume is connected to an outlet line connecting to a recycling bin so that the pre-pressure in the auxiliary volume is equal to the working pressure in the recycling bin. - can be brought into a first state in which the auxiliary volume is vented toward the ambience of the refrigerant compressor so that an atmospheric normal pressure is caused to prevail in the auxiliary volume, - can be brought into a second state in which the auxiliary volume, while being gas-tight and having a constant pre-pressure p0, is operative as a gas pressure spring, - can be brought into a third state in which the auxiliary volume is connected to an inlet line connected to a refrigerating system so that the pre-pressure in the auxiliary volume is equal to the working pressure in the refrigerating system, and - can be brought into a fourth state in which the auxiliary volume is connected to an outlet line connecting to a recycling bin so that the pre-pressure in the auxiliary volume is equal to the working pressure in the recycling bin.