Performed preventative maintenance for a high efficiency Lennox system model #sl280uh110V60c, serial #5916E13676. Removed and cleaned carbon off of the flame sensor, cleaned out the burners and burner box. Checked all electrical connections to ensure that they are secure and in good condition. Replaced the air filter size 20x25x1. Tested the drain line and condensate pump with several bottles of water to ensure that there are no leaks or clogs. Tested the system by calling for heat. I observed the system starting normally. Took a combustion analysis test and got the following readings, o2 is at 11.9%, co is at 9ppm. The inducer amp draw is at .20, the blower amp draw is at 9.2. The system is operating properly at this time. I checked the condenser due to the homeowner stating that it makes a loud noise when shutting down. I cycled the power on and off to hear the noise the homeowner was talking about. Due to the weather conditions I was not able to open the electrical box to confirm t