Did a preventative maintenance on a Lennox gas furnace. During the maintenance I clean the flame sensor I also cleaned out the burner box and the blower motor housing and dusted off the entire unit. Also changed out the customer supplied filter also did a combustion test the CO level was 22 and the O2 level was 17 I also did an amp reading on the inducer motor and the blower motor which both meet the furnace specs. Also went over all electrical connections to make sure they were tight and secure. System is operating properly at this point. M#SL280UH090V36B-03 s#5914L26127