Did a Maintenance on a gas furnace. Cleaned the flame sensor, an inducer port. Also, cleaned the blower motor housing and the burner compartment. Did a amp check on the inducer and blower motor both are in rang. Did a combustion test the CO was 43 customer changed the 20x25x1 filter. System is operating properly at this time. M#G8mxn1352420a2 s# a123215436