Performed preventative maintenance for a carrier furnace. I observed the system starting normally. I took a combustion analysis test and got the following readings, o2 is at 16%, co is at 58ppm and the system is operating at 91% efficiency. I observed the system shut down normally. Removed and cleaned carbon off of the flame sensor. Cleaned out the burners and burner box. Checked all electrical components needed for heating. Replaced the air filter 16x25x1. Made sure the drain line is clear. Amp draws are 6.5 for the blower motor and . 53 for the inducer motor.