The present invention relates to a device for controlling a working fluid with low freezing point circulating in a closed loop (10) working on a Rankine cycle, said loop comprising a compression/circulation pump (12) for the fluid in liquid form, a heat exchanger (18) swept by a hot source (24) for evaporation of said fluid, expansion means (30) for the fluid in vapour form, a cooling exchanger (42) swept by a cold source (F) for condensation of the working fluid, a working fluid tank (48) and working fluid circulation lines (52, 54, 56, 58, 60, 62). According to the invention, tank (48) is connected to a depression generator (50).
