1. Visually inspected condenser coil for debris/ dirty. 2. Inspected condenser fan motor. 3. Inspected condenser fan blades. 4. Inspected/ cleaned wiring connections. 5. Tested for gas leaks 6. Tested functionality and cleaned flame sensor 7. Tested functionality and cleaned pressure switches and ports 8. Inspected / replaced return filter. 9. Inspected return plenum for debris/ dirty. 10. Inspected evaporator coil. 11. Tested functionality and visually inspected surface igniter 12. Checked blower amp draw. 13. Measured temperature differential from supply to return. 20 degrees measured. 14.Drain line tested with gallon of water for clogs and to push anything trying to solidify out Found large amount of dust in return plenum and a decent bit of dust on the blower wheel. Since I am seeing this much dust on the blower wheel it is inevitable that the evaporator coil is just as dirty since they are both after the filter. Upon proceeding to the outdoor unit I noticed that the outdoor uni