I have a ych240a3h0ab. The unit is cycling on limit switch. I have 65 return 130 supply. This is in a church diffucult to get cfms. The gas at manifold -.02. I am going to clean evap coil. I did take duct apart and airflow seems ok. I may have to traverse. The heat exchanger looks ok. This unit is 20 years old. The inducer, ignitor and high limit were replaced. Does anyone know what the temp rise should be?? Any thoughts