Depending on car you may have a pollen filter than can be cleaned or replaced. That can be got at from under the glovebox. If you have you you'll see 3 little black mushroom shaped bits facing towards the back of the car. Pull them out then a panel pulls down and the 2 filters slide out. But if you dont have that im not sure of your options, the fan is to the left of that tucked up behind your glove box thats probably where id start.