This article is the third and final part of a three-part series on inspecting and servicing gas appliances. The information contained throughout this article series follows the gas furnace check sheet provided in the PDF link below. (Click on the link "Equipment Check Sheet" at the bottom of this article.) I would recommend that you make several copies of this check sheet to use on jobs as a reference source.
Every furnace should be adjusted to operate under the manufacturer's prescribed guidelines as suggested in the installation instructions and listed on the furnace label. With every furnace, usually only two parameters are adjustable in the field: airflow and manifold pressure. All other aspects of operation are governed by these two parameters.