System comprising a refrigerant compressor and an electronic control device for the refrigerant compressor, which refrigerant compressor at least comprises - a drive unit, - a compression mechanism which is operatively connected to a rotor of the drive unit and has at least one piston which can be moved back and forth in a cylinder of a cylinder block and can be driven via a crankshaft, in order to cyclically draw refrigerant into the cylinder during a suction phase and to compress the refrigerant in the cylinder during a compression phase following the suction phase, wherein the electronic control device is adapted - to detect and control and/or regulate a rotational speed (ω) of the crankshaft, - to detect at least approximately a piston position of the piston, characterized in that the electronic control device is adapted - when the drive unit is switched off, to determine an energy assessment variable difference which is proportional to an energy required to perform one crankshaft revolution, - at a measuring speed (ω), to determine an energy assessment variable (E(ω)) which is proportional to a rotational energy at the measuring speed (ω) as well as the number of crankshaft revolutions that are left until the stop of the compression mechanism, with the drive unit switched off, - to check whether the crankshaft revolutions that are left, when the drive unit is switched off at a reference piston position, allow the compression mechanism to stop in its suction phase, - optionally, to switch on the drive unit and, taking into account the energy assessment variable difference, to determine a switch-off speed (ω switchoff) at which the drive unit is to be switched off at the reference piston position in order to bring about a standstill of the compression mechanism in the suction phase and to switch off the drive unit at the switch-off speed (ω switchoff), - or, optionally, to switch on the drive unit and to operate it at a pre-determinable limit speed (ω limit) and to determine a switch-off piston position taking into account the energy assessment variable difference and to switch off the drive unit at the limit speed (ω limit) and the switch-off piston position. - a drive unit, - a compression mechanism which is operatively connected to a rotor of the drive unit and has at least one piston which can be moved back and forth in a cylinder of a cylinder block and can be driven via a crankshaft, in order to cyclically draw refrigerant into the cylinder during a suction phase and to compress the refrigerant in the cylinder during a compression phase following the suction phase, wherein the electronic control device is adapted - to detect and control and/or regulate a rotational speed (ω) of the crankshaft, - to detect at least approximately a piston position of the piston, characterized in that the electronic control device is adapted - when the drive unit is switched off, to determine an energy assessment variable difference which is proportional to an energy required to perform one crankshaft revolution, - at a measuring speed (ω), to determine an energy assessment variable (E(ω)) which is proportional to a rotational energy at the measuring speed (ω) as well as the number of crankshaft revolutions that are left until the stop of the compression mechanism, with the drive unit switched off, - to check whether the crankshaft revolutions that are left, when the drive unit is switched off at a reference piston position, allow the compression mechanism to stop in its suction phase, - optionally, to switch on the drive unit and, taking into account the energy assessment variable difference, to determine a switch-off speed (ω switchoff) at which the drive unit is to be switched off at the reference piston position in order to bring about a standstill of the compression mechanism in the suction phase and to switch off the drive unit at the switch-off speed (ω switchoff), - or, optionally, to switch on the drive unit and to operate it at a pre-determinable limit speed (ω limit) and to determine a switch-off piston position taking into account the energy assessment variable difference and to switch off the drive unit at the limit speed (ω limit) and the switch-off piston position.