Complete 2 system furnace repair and preventative maintenance check. Change both filters, check safety and operations. Find upstairs system operating but did have a misfire and the customer stated that some time blower starts up and shut off and start back up again. Customers may have control starting to fail but will need to keep a check. Coil badly rusted, ignition worn and system high O2 level. Find downstairs operating with worn motor and dirty, find flame sensor weak and rusted coil.