Red shield fall service. Replaced filter. Blower motor run capacitor checked good, rated 15uf, actual 14.8uf, within mfg specs, motor and wheel are clean, hot surface ignitor checked good, cleaned and checked flame sensor, pressure switches (2) checked good, inducer motor run load amps are good, rated 2.8A actual 2.4A, roll out switches (2) checked good, high limit switch checked good, manifold pressures are good ( low fire 1.67in wc, high fire 3.48 in wc. Checked system operation with tstat. System is operating normally. Conducted carbon monoxide test—0ppm. There are no carbon monoxide detectors in home. Recommend that detectors be installed Some supply registers are showing dirt. Generated an estimate for a duct cleaning for 17 ducts. Explained to homeowner that after initial cost of duct cleaning, that as long as they maintain there Red shield agreement that Interstate will clean ducts every 3 yrs at no cost to homeowner.