A fan will draw air across the evaporator coils at a properly functioning air conditioner, in which it’s cooled, then be re-circulated back in the room. If the air filter is dirty or clogged, then there might be little if any airflow within the evaporator coils, making them overly cold, and frost or ice may form them on, limiting the airflow much more. This is going to lead to no or little cool air being dispersed to the room.