Upon arrival immediately noticed outside condenser for upstairs system was extremely iced over. Further inspection found air handler evaporator coil extremely frozen. Dirty 20x25x4 filter but not dirty enough to cause airflow restriction and freeze coil. Anticipating refrigerant loss due to all other components are functioning. System requires 24hours to thaw to perform proper diagnostic. Informed homeowner that all breakers are off to prevent operations to thaw system. Scheduling return trip for diagnostics after 10am Thursday.