The working fluid composition for a refrigerating machine of the present invention comprises: a refrigerating machine oil comprising a mineral oil and an alkylbenzene in a mass ratio, the mineral oilthe alkylbenzene, of 8515 to 1585, wherein the mineral oil has a % CN by n-d-M ring analysis of 20 to 60, a pour point of \u221215\xb0 C. The actuator comprises a piston cylinder having a floating cushion piston supported within the cylinder end to support the piston within the cylinder in a retracted position at a prescribed spacing from the cylinder end. When the available bandwidth at that pre-defined location is less than the bandwidth required to convey the signals carried along all these active channels, a rate adjusting mechanism is applied to at least one of the active channels, while repeating this check periodically.