Abstract: In a cooling fluid circuit comprising a compressor, a condenser, an expansion valve and an evaporator, a heat exchanger is provided to transfer heat from the duct arriving at the expansion valve to the duct arriving at the compressor, so as to condense the residual vapor and/or to vaporize the residual liquid respectively which may be found therein. The fluid reaching the expansion valve and the fluid reaching the compressor are thus practically free from a vapor phase and liquid phase respectively, which improves the operation of the device. The invention is particularly applicable to the air-conditioning of the passenger space of motor vehicles.