The issue of an AC running constantly but not cooling is likely due to a few possible causes. Firstly, the air filter may be clogged or dirty, preventing proper airflow and reducing efficiency. Secondly, the evaporator coil may be frozen over due to low refrigerant levels or restricted airflow. Lastly, the thermostat could be malfunctioning or set incorrectly. For an optimal repair, it's advisable to get in touch with a San Diego HVAC specialist if any of these problems are present.