The answer to 'when to service system upgrade' is that you should have your HVAC system serviced and upgraded on a regular schedule, typically once or twice per year. This helps ensure your system is running efficiently and safely, extends its lifespan, and can prevent costly breakdowns.
For most homes, it's recommended to have a professional HVAC technician perform a full system inspection and tune-up in the spring before the cooling season, and again in the fall before the heating season. This allows them to check for any issues, replace air filters, clean components, and make adjustments as needed.