Most cars today have a cabin air filer, this is fairly new in the automotive industry and it works great. It filters the air that is blowing in your face from your A/C and wow do these filters get nasty. they are usually located behind the glove box in the duct work, it needs to be replaced about once a year depending on where you drive. If you are getting a musty or bad odor from your a/c.. you might need a new cabin filter, we also recommend treating the A/C system at that time. This cleans out the mildew and leaves a fresh clean scent in your car!