Performed system maintenance Lincoln. Some one added a filtered fresh air vent into the return plenum. Filter is very very dirty. System hasn’t been serviced in awhile. Furnace carrier 16 yrs old. Blower capacitor 10@7.9mfd, low well below manufactures recommend specs. Recommend replace. Duct work silver flex sealed with mixing boxes, found one mixing box on platform has hole in it big enough to put a finger in. Hot surface ignitor ok 60 ohms. Cycled heating system with nest thermostat, then switched to ac. Dual capacitor ok 55-5, contactor has been replaced. And system has hard start kit. Data plate for ac has worn off. Ac refrigerant pressures slightly low, but normal for it only being 50 outside. Signed up on membership, installed new 10 mfdblower capacitor. And sealed hole in mixing box at no charge for signing up today.