What would cause air not to blow out of the vents?

Air may not blow out of the vents due to several issues, including a clogged air filter, which restricts airflow. Other potential causes include a malfunctioning blower motor, blocked ductwork, or issues with the HVAC system's thermostat. Additionally, a closed or partially closed vent can also prevent air from circulating properly. Regular maintenance can help prevent these problems.