There are several possible reasons why a residential AC unit may be running but not effectively cooling your home. It could be due to a dirty air filter that restricts airflow, preventing proper cooling. Another common issue is a refrigerant leak, which can result in reduced cooling capacity. Faulty or worn-out components like the compressor, condenser, or fan motor may also be contributing factors. Additionally, improper thermostat settings, inadequate insulation, or ductwork problems could affect cooling performance. It is advisable to consult with a qualified HVAC technician who can diagnose the specific issue and provide the necessary repairs or adjustments to restore proper cooling functionality.