Preventative maintenence inspection on Carrier high efficiency furnace. 20x25x4 air filter is new today. Clean flame sensor and check ignitor ohms. Flush condensation trap and drain lines. Run test unit in heating mode. Initial startup shows furnace operating with 3.8inwc of gas supply. This is at the top of the range and can cause short-cycling. Adjusted gas pressure to 3.0inwc at the low end of the range. This will prevent short cycling and allow the furnace to run longer and more evenly heat the house. Temperature rise is within specs. Blower and inducer motors tested good. Pvc flue vents in good condition and no sign of leaks. 0PPM CO detected during testing. System is operating properly, efficiently and ready for Winter.