An auxiliary air-conditioning system for a motor vehicle, in particular a truck comprising a tractor provided with a driving cab and possibly a sleeper compartment, and a primary air-conditioning system connected to the main engine and to the battery of the truck. The auxiliary air-conditioning system is totally independent of the primary air-conditioning system of the truck and is formed by an external unit designed to be set on the outside of the driving cab and/or of the sleeper compartment, and by at least one heat-exchange unit, which is hydraulically and electrically connected to the external unit and is designed to be set inside the driving cab and/or inside the sleeper compartment.