#iaq upon arrival for tune up 9 year old systems on and cooling. Customer states issue with smell coming from system and drain lines. Inspected outdoor units. Fan and compressor amp draws within unit specifications. Capacitors within tolerance. Refrigerant pressure good. Inspected indoor units. Downstairs unit drain lines routed both through primary. Also found paper notebook inside of systems coil. Notebook covered in growth and could be responsible for smell. Blowers clean. Coils have slight corrosion buildup. Recommended repairing drains and installation for drain safteys. Customer agreed. Left system on and cooling.