Performed preventative maintenance on furnace. Customer changed filters recently, so I supplied her with filters to change when due. Inspected the blower assembly, motor, capacitor, electrical components, heat exchanger, burners, flame sensor, ignitor, gas valve, pressure switch, inducer motor and overall condition of equipment. Customer has a weak blower capacitor, most likely due to stress on blower from high static pressure due to return being undersized. Informed customer about the repair needed. Customer is aware of what we discussed, but doesn’t want to do anything at this time. I cleaned the flame sensor and dust off the burners and components. Checked thermostat operation, wiring, amps, temperatures and gas pressure. System is operating normally at this time.