Did they maintenance on a Lennox gas furnace. During the maintenance I clean flame sensor and ohm the HSI. Also did a combustion test the PPM was 21 and the O2 was 19. Cleaned out the burner box and the blower motor housing. And I did an amp check on the inducer motor and blower motor which both meet the furnace specs. And changed out the 16 x 25 x1 Filter. System is operating properly at this point m#EL280UH070E36A-01 s#5919G14317 customer would like receipt mailed to them.