The answer to 'why is my air filter not working' is that the air filter may be clogged, damaged, or installed incorrectly. A clogged air filter can restrict airflow and reduce the efficiency of your HVAC system. Symptoms of a bad air filter include reduced airflow, higher energy bills, and reduced indoor air quality.
To fix the issue, you should first check the air filter and replace it if it's dirty or damaged. Make sure the new filter is the right size and installed properly. If the problem persists, there may be other issues with your HVAC system that require professional diagnosis and repair.