Did a preventative maintenance on a Lennox gas furnace. During the maintenance I clean the flame sensor. Also, I cleaned out the burner box and the blower motor housing. I also did an amperage check on the inducer motor and the blower motor which both need the furnace specs. I also cleaned out the inducer port. I also shop vac to return out due to a lot of contractor dust due to this I’m gonna recommend a duct cleaning. Also did a carbon monoxide check the CO level was 49.4 and the O2 level was 11.2. Changed out to 16 x 25x1 filter. System Is operating properly at this point. I am also going to recommend a REME-halo to increase air quality.M#ML180UH090P36B-53 s#1715E14582