Upon arrival to install water safety switch, found primary drain line with condensation at a stand still and overflowing from air vent into attic space; attempt to flush primary drain line met resistance and was unable to clear; removed water from line and installed water safety switch to prevent the potential for future overflow; installed dual capacitor and ran system to cool; at this time there is no water in coil pan, exit ports are clear and free of debris; recommended plumbing inspection to solve primary drain line inability to remove condensation.