If you don't replace your cabin air filter, it will become increasingly clogged with dirt and debris, compromising the efficiency of your car's filter and HVAC system. This will reduce the volume of air in the passenger compartment, resulting in bad odors and poor air quality. Allergens will enter the car without being filtered, and this can cause serious health issues for people with allergies or breathing difficulties. In addition to air quality, not changing the cabin air filter is a safety issue and a maintenance requirement for the climate control system.
If you smell an unpleasant scent coming from the air conditioner, it is likely that your air filters are not working properly. It is important to change the cabin air filter regularly to prevent pollen from entering the vehicle and causing passengers to start sneezing. A new cabin air filter will also ensure that passengers don't have to roll down windows in the middle of winter to get fresh air. A dirty or clogged cabin air filter will reduce the amount of air flowing through the vents, causing the HVAC system to work harder than necessary and possibly burning out the engine ahead of time.
It can also cause condensation to form on the windshield. A good rule of thumb is to replace your cabin air filter every February, before spring allergy season hits, especially if you live in an area with lots of trees. One of the first signs that you need to replace the air filter is weak ventilation airflow into the cabin. Dirty or excessively clogged cabin air filters can produce a dusty and damp odor when the HVAC system is turned on.