A portable air conditioning unit, which can be arranged in an enclosed environment of the type of a compartment, cabin, or internal space of a motor vehicle, in order to modify the temperature levels, relative humidity, and the like, comprising at least one duct through which a heat transfer fluid flows, affected sequentially by at least one compressor, for raising the temperature and pressure of the heat transfer fluid in the gaseous state, by at least one condenser, for carrying off heat from the heat transfer fluid and its passage from the gaseous state to the liquid state, by at least one lamination element in which said heat transfer fluid expands, for lowering the pressure of the heat transfer fluid in the liquid state, and by at least one evaporator, for absorbing heat by means of the passage of the heat transfer fluid from the liquid state to the gaseous state, the unit further comprising means of natural, not forced, collection and conveyance, toward said condenser, of condensed water which may have formed along the outer surfaces of said evaporator, for the evaporation thereof by means of the heat carried off from the heat transfer fluid, said means comprising at least one tank, arranged below said evaporator, for the collection of the condensed water, and a layer of highly capillar material, partially accommodated in said tank, for the impregnation thereof with the condensed water collected in said tank, at least one end lip of said layer touching said condenser, for the natural conveyance, by capillary action, of the condensed water toward said condenser and the evaporation thereof by means of the heat carried off from the heat transfer fluid, characterised in that the unit further comprising a first fan, facing toward said condenser, for the forced circulation of a first fluid to be heated by way of said condenser, said means comprising a receptacle, arranged substantially below said condenser and facing toward said first fan, placed in connection with said evaporator for the collection of the condensed water, the rotation of said first fan driving the water collected in said receptacle against said condenser, for the evaporation thereof, and said means comprising said tank and said receptacle, for the collection of the condensed water in said tank and a first transport thereof by capillary action, by way of said layer, to said condenser, the water that is not evaporated being collected in said receptacle for a second transport to said condenser, by way of said first fan, the unit further comprising a pair of tubes, each one of said tubes leading, with a corresponding first free end, outside the enclosed environment, on the opposite side said tubes being selectively associable with one of said pair of air exit ports and said pair of entrances, for the expulsion respectively of the second fluid or of the first fluid to the outside of the enclosed environment, and the corresponding heating or cooling of the enclosed environment, and the unit further comprising an interface plate, having a shape and size adapted to the juxtaposition thereof to an opening of the type of a window of the motor vehicle, for the closure thereof, said plate being provided with respective slots that can be fixed to the free end of a pair of tubes, on the opposite side said tubes being selectively associable with either said condenser or said evaporator, and the corresponding cooling or heating of the enclosed environment, said plate being made of a transparent material, preferably selected from methacrylate and polycarbonate.