Refrigerant fluid circuit for thermally conditioning a cabin of a vehicle, comprising: - a first branch in which are installed in series at least one compressor and an interior exchanger designed to ensure thermal exchange between the refrigerant fluid and an air stream, termed the interior air stream, intended to be dispatched into the cabin, - a second branch in which are installed in series at least one first means of control of the circulation of the refrigerant fluid in said second branch, a first expansion member and an evaporator, - a third branch in which are installed in series at least one second expansion member and an exterior exchanger designed to ensure thermal exchange between the refrigerant fluid and an air stream, termed the exterior air stream, arranged outside the cabin, - said first branch being in series with the second branch and the third branch, said second branch being in parallel with said third branch, - a means for placing the third branch in communication with the second branch, said means being installed between a sector of the third branch situated downstream of the exterior exchanger and a portion of the second branch situated upstream of the first expansion member, characterized in that the circuit is designed to operate according to a mode of heating where a quantity of heat absorbed by the exterior exchanger is dissipated in the interior air stream by the interior exchanger, according to a mode of cooling where a quantity of heat absorbed by the interior exchanger is dissipated in the exterior air stream by the exterior exchanger, and according to at least three modes of dehumidification which combine the mode of heating and the mode of cooling, and in which a refrigerant fluid circulates in the same direction whatever the mode. - a first branch in which are installed in series at least one compressor and an interior exchanger designed to ensure thermal exchange between the refrigerant fluid and an air stream, termed the interior air stream, intended to be dispatched into the cabin, - a second branch in which are installed in series at least one first means of control of the circulation of the refrigerant fluid in said second branch, a first expansion member and an evaporator, - a third branch in which are installed in series at least one second expansion member and an exterior exchanger designed to ensure thermal exchange between the refrigerant fluid and an air stream, termed the exterior air stream, arranged outside the cabin, - said first branch being in series with the second branch and the third branch, said second branch being in parallel with said third branch, - a means for placing the third branch in communication with the second branch, said means being installed between a sector of the third branch situated downstream of the exterior exchanger and a portion of the second branch situated upstream of the first expansion member, characterized in that the circuit is designed to operate according to a mode of heating where a quantity of heat absorbed by the exterior exchanger is dissipated in the interior air stream by the interior exchanger, according to a mode of cooling where a quantity of heat absorbed by the interior exchanger is dissipated in the exterior air stream by the exterior exchanger, and according to at least three modes of dehumidification which combine the mode of heating and the mode of cooling, and in which a refrigerant fluid circulates in the same direction whatever the mode.