The most common cause of low airflow from your vents is a blocked or dirty AC filter. When your filters are dirty, or the return air grill is blocked, it decreases the efficiency of your entire AC system and significantly reduces its ability to cool your home. Be sure to keep the area around your AC filter clear and clean or change your AC filter once a month during heavy-use times like summer. Other causes of low airflow include bad blower motors, frozen coils, or ducts that have split open.