To prevent this last situation from occurring, Behr Hella Service recommends motorists to have their air-conditioning systems checked once a year or every 15,000 km. This check includes replacing the cabin air filter that removes dust, pollen and particles of dirt. These filters have only a limited capacity, and after about a year they can no longer adequately ventilate the vehicle and clear fogged windows. The annual check also inspects and tests all the components and the air-conditioning system as a whole, if necessary also disinfecting the evaporator, whose fins provide a dark, damp environment that is an ideal breeding ground for bacteria and fungal spores. The thermal management expert also advises a full air-conditioning service every two years. This provides the same benefits as the annual air-conditioning check, plus a complete change of refrigerant, a check for any leaks and a new filter drier. The filter dryer removes particles of dirt from the refrigerant and binds the moisture, but its capacity is limited, and once this is exhausted any excess moisture in the air-conditioning system can release acids that attack and corrode the individual components.