Performed preventative maintenance for three heating systems. System #1 located in the basement. Goodman furnace model #Gmec960603bnac, serial #1709461929. Upon arrival I called for heat and took a combustion analysis test and received the following readings, 02 is 7.4% and the co levels are 58ppm. I powered the system down and removed and cleaned carbon off of the flame sensor. Cleaned out the burners and burner box.Replaced the air filter size 16x24x1. Tested the drain line and condensate pump with several bottles of water to ensure that there are no leaks or clogs. Checked all electrical connections to ensure that they are secure and in good condition. The blower motor and blower wheel are clean and in good condition. I powered the system back up and called for heat. The inducer motor amp draw is within normal range and the blower motor amp draw is at 3.4. The system is operating properly at this time. Performed preventative maintenance for a high efficiency Lennox furnace model #E