During the hot summer months, contaminants, such as pollen, dust, mold spores and smog, can easily enter a vehicle’s passenger compartment through the air conditioning, heating and ventilation systems, making the air in the car six times dirtier than the air outside.. Motorists can protect themselves and their passengers from these containments by replacing the vehicle’s cabin air filter annually or more often in areas with heavy containments, or whenever heating or cooling efficiency is reduced. Cabin air filters clean the incoming air and remove allergens. If your vehicle is model year 2000 or newer, there’s a good chance it is equipped with a cabin air filter. Check your owner’s manual. If the cabin air filter is not replaced, it can cause musty odors in the vehicle, and over time, the heater and air conditioner may become damaged by corrosion.