The answer to 'why is my evaporator coil short cycling' is that it's likely due to a problem with the airflow over the coil. This can be caused by a clogged air filter, a malfunctioning blower fan, or blocked ductwork. When the airflow is restricted, the evaporator coil can get too cold and trigger the safety controls to shut the system off prematurely.
Short cycling can also be a sign of a refrigerant leak, a problem with the compressor, or issues with the thermostat. If the evaporator coil is icing over, it may be a sign of a more serious problem that requires professional diagnosis and repair.