When, according to the invention, the air in the so-called Zone 2 areas is ventilated, i.e. sucked out, the ATEX Directive concerning treatment of inflammable coolants may be satisfied in an effective manner. In practice, the suction around the engine (6) of the vehicle and the ventilation of the service equipment (9, 21, 53), respectively, may ensure that the requirements in the ATEX Directive with respect to Zone 2 areas may be satisfied, if possibly inflammable vapors are discharged, since these areas are ventilated to the atmosphere. The use of the method is service-friendly when servicing air conditioning systems and when adding coolant online.