In order to improve a refrigerant compressor for refrigerating systems comprising at least one cylinder unit, which has a cylinder housing and a piston which can move in an oscillating manner in the cylinder housing, a cylinder head, with an inlet chamber, flowed through by an inlet flow of the at least one cylinder unit, and with an outlet chamber, passed through by an outlet flow of the at least one cylinder unit, and a switching valve for interrupting the inlet flow in such a way that it can be operated in any desired part-load range, it is proposed that a control for activating the switching valve is provided, which control, for operating the refrigerant compressor in a lower part-load range, operates the switching valve in successive switching intervals, respectively comprising an opening interval and a closing interval of the switching valve, which are shorter than a shortest time period after which a temperature of an evaporator in the operating refrigerating system has risen by approximately 10% during an interruption of the inlet flow.