It is then passed through a heater matrix, inside of which the engine's coolant circulates, where it can be reheated to a certain degree or even a certain temperature selected by the user and then delivered inside the vehicle's cabin through a set of adjustable vents. Another way of adjusting the desired air temperature, this time by working on the system's cooling capacity, is precisely regulating the centrifugal fan speed so that only the strictly required volumetric flow rate of air is cooled by the evaporator. The user is also given the option to close the vehicle's external air flaps, to achieve even faster and stronger cooling by recirculating the already-cooled air inside the cabin to the evaporator. Finally, whenever the compressor is able to be commanded to operate in a reduced displacement, the vent temperature can also be controlled by acting upon the compressor's displacement. Evaporator freeze over, which stops air from flowing through the evaporator fins, can be prevented in different ways. A temperature switch or a thermistor can control the evaporator coil surface temperature, and a pressure switch or sensing element can monitor the suction pressure (which is in relationship with the refrigerant's evaporating temperature). Both control means can act (either directly or by means of a control unit fed by their data) upon the compressor's clutch engagement status or, in the case of a variable displacement compressor, its displacement; additionally, a secondary valve located on the suction side can throttle the refrigerant flow so that the evaporator's outlet pressure doesn't fall below a precise value during system operation. To complete the refrigeration cycle, the refrigerant vapor is routed back into the compressor. The warmer the air that reaches the evaporator, the higher the pressure of the vapor mixture discharged from it and therefore the higher the load placed on the compressor and therefore on the engine to keep the refrigerant flowing through the system. Compressor load is also proportional to the condensing temperature. The compressor can be driven by the car's engine (e.g. via a belt, often the serpentine belt, and an electromagnetically actuated clutch; an electronically actuated variable displacement compressor can also be always directly driven by a belt without the need of any clutch and magnet at all) or by an electric motor. There are different methods for the repair and maintenance of the tube connections ensuring the refrigeration cycle. Conventional methods like soldering