Furnace clean and tune. Cycled system. Checked heat exchanger. Two chambers have deep etching in them. This is where cracks are starting to form. Checked, removed, and cleaned burners and flame sensor. Both ok. Igniter tested normal. Checked and tightened electrical connections and clamps. Cleared drain line,checked and adjusted gas pressures to maximize efficiency. Preformed combustion test. Found higher levels of XS air in exhaust. This is indicating some blockage in secondary heat exchanger. No CO found in airstream. Ventor motor bearings are worn. This is causing noisy and operation with vibration. This will seize at some point. Average life expectancy for this unit is 14 years. This unit is well past that expectation and is worn. Due to age, condition, and cost of repair, second opinion is recommended. No need to return for a pressure check, this unit is not a pulse system. Job complete.