Arrived to do a performance maintenance. Reassembled the wall that was taken down to allow plumbing repairs. Replaced furnace filter and humidifier panel. Set up for combustion analysis temperature split and static pressure tests. Verified operation of all mechanical and electronic components of the furnace. Checked blower for cleanliness and to see if there is any play in the bearings. Found that the fan for heating and cooling is coated in dust debris. Checked systems heat exchanger to ensure proper venting of flue gas. While checking the heat exchanger found bacterial growth present on the evaporator pan. Verified operation of the humidifier. Found that the solenoid valve on the humidifier is not closing completely. Furnace and humidifier are operational at this time.