The answer to 'why is my air filter freezing up' is that a frozen air filter is usually caused by a problem with airflow. This can happen when the filter is clogged, the blower fan is not working properly, or the refrigerant level is low. A frozen filter restricts airflow, which causes the coil to get too cold and freeze up.
Some common symptoms of a frozen air filter include reduced airflow, icy buildup on the filter, and the system not cooling effectively. To fix this, you'll need to identify and address the underlying cause, such as replacing a clogged filter, cleaning the blower, or recharging the refrigerant. In some cases, you may need to call an HVAC technician to diagnose and repair the issue.