Addressed residential split-system AC failure. Diagnostic tests revealed faulty dual-run capacitor and worn contactor. Replaced 45/5 μF capacitor and 40A contactor, ensuring proper voltage to compressor and fan motors. Cleaned condenser coils using foaming cleaner, improving heat rejection. Checked refrigerant charge, finding slight undercharge. Added R-410A to achieve 10°F subcooling. Verified proper amp draw on all motors and measured supply air temperature drop. System now operating at peak efficiency with 20°F delta T.