The engine in your Ford Fusion has an air filter that keeps abrasive particles out of your engine components, but it also has a filter that does the same for the passenger cabin. Cabin air filters were rare on American cars before 2000, but have since become fairly standard. However, they only work well when they provide a free flow of air, so be sure to check them every 3 months or so, and replace them when they appear dirty.
Pull the bonnet release latch in front of the driver's seat to release the bonnet. Lift the bonnet and lift the support arm to prop it up.
Look at the area just in front of the passenger side windshield wiper. You will see a rectangular, black plastic case with a removable lid. Unfasten and remove the lid to expose the cabin air filter.
Note the direction of the arrow printed on the outside edge of the cabin air filter. This indicates the direction of the air flow. You must install the new filter with the air flow going in the same direction.
Remove the old air filter. If you're not sure if it needs replacement, examine it closely. If it is more than 3 months old and visibly dirty, it's time for replacement.
Put the new air filter in the compartment with the air flow direction arrow pointing in the direction you noted in Step 3. Replace the lid on the compartment, and push it down until it snaps snugly into place.
Lower the support arm on the bonnet and close the bonnet.
If you fail to replace this filter regularly, you may experience more irritants and allergens inside your car's passenger compartment, as well as unpleasant smells.
Air must pass through these filters before coming out of your vents or defrosters, so if they're severely clogged, you may not be able to get heat, ventilation or windshield defrosting when you really need it.