Performed tune up on 13 year old Ruud Furnace. Customer stated that they haven’t turned on the heater yet, and wanted to have it serviced first. Customer already changed the filters. I started with a thorough inspection of the internals of the furnace. I inspected the blower assembly, electrical components, heat exchanger, coil, burners, flame sensor, ignitor and overall condition. I cleaned the flame sensor and brushed dust off the burners. System is starting to show its age, and is in need of some cleaning. Duct work is dusty internally, and the blower wheel needs to be cleaned. The heat exchanger has some hot spots, but is still intact and no signs of cracks at this time. I did recommend the ductwork be cleaned, as well as the blower. I checked thermostat operation, wiring, capacitor, amps, temperature rise and gas pressure. System overall is still heating properly within manufactured specifications, just needs some cleaning to keep it running.