I performed preventive maintenance on a single AC zone today. I inspected and cleaned the evaporator and condenser coils using Nu-Calgon Evap-Fresh, replaced the air filter with a MERV 11 pleated model, and checked refrigerant levels. I also tested capacitors, verified proper amperage draw on all motors, and lubricated moving parts. The condensate drain line was cleared with nitrogen, and I calibrated the thermostat. Finally, I checked all electrical connections, inspected ductwork for leaks, and tested the system's overall performance in both cooling and fan-only modes.