Diagnosed faulty Honeywell TH8320R1003 thermostat in Denville, NJ home. Multimeter testing revealed intermittent 24V power supply. Traced issue to corroded C-wire connection at air handler. Replaced damaged wire segment and secured connections. Installed new Ecobee SmartThermostat with voice control as upgrade. Configured for 2-stage cooling and single-stage heating. Performed system test: verified proper staging, fan operation, and Wi-Fi connectivity. Calibrated temperature sensor to ±0.5°F accuracy. Demonstrated energy-saving features to homeowner.