The answer to 'air filter not turning on' is that there could be several common causes, such as a problem with the power supply, a malfunctioning thermostat, or a blockage in the air filter itself. Symptoms may include poor air flow, reduced heating/cooling efficiency, and potentially higher energy bills.
Some solutions you can try at home include checking the power supply to the air filter, inspecting the thermostat settings, and replacing the air filter if it's dirty or clogged. However, if the issue persists or you're not comfortable troubleshooting it yourself, it's best to call in a professional HVAC technician to diagnose and fix the problem.