Performed preventative maintenance for a Lennox furnace model #SL280UH090V36B04, serial #59198A35010. I powered the system down and removed the access panels. Removed and cleaned carbon off of the flame sensor and cleaned out the burners and burner box. Checked the pressure switch for clogs and replaced the air filter size 20x25x5. Checked all electrical connections to ensure that they are secure and in good condition. Tested the drain line for leaks and clogs. I powered the system back up and called for heat. I took a combustion analysis test and received the following readings, o2 is at 12.6% and the co levels are 2ppm. The inducer motor amp draw is at .22 and the blower motor amp draw is at 3.62. The supply temp is at 116°f. The system is operating properly at this time.