Did a maintenance on a gas furnace. Did a combustion test the ppm was 17 an o2 was 11. Cleaned the flame sensor, and ohm out the HSI. Did a amp check on the inducer an blower motor and both met the furnace specs. Cleaned out the burner box and blower motor housing . Customer changed the 16x25x4 filter. System is operating properly at this time. M#ML180UH110E60C-54 s#1720C21935