Cleaned & checked gas furnace. Inspected heat exchanger & flue venting. cleaned burners & flame sensor. Customer complaint: customer heard a banging noise for a few minutes. Found no unusual noises at this time. Checked voltage & amp draw of motors. Tested capacitors. Found run capacitor weak: 24%low. Replaced capacitor and tested amp draw. Clean and check humidifier, replace pad, checked water flow and drain. Calibrated h-stat.