Did a preventative maintenance on a gas furnace during the maintenance I clean the flame sensor check pressure switch. I also did amp drawls on the inducer motor and the blower motor which both meet the furnace specs. I also checked the condensate pump to make sure that was still working as well as cleaning out the trap on the high-efficiency furnace. I also did a humidifier maintenance where I switched out to 35 panel. And also made sure system was draining properly and it was. Customer thought he smelled gas I could not but I tightened up the union just to ensure it was not. Switched out a Merv 16 filter. Did a combustion test the CO levels were 19 and the oxygen levels was 11.8. System is operating properly at this time. M#G61MPV-60C-111-12 s#5911G11994.