Furnace clean and tune. Cycled system. Checked heat exchanger, found all chambers are very rusted and corroded with deep etching and cracks starting in all chambers. Checked, removed, and cleaned burners and flame sensor. Burners are very rusted and damaged. Flame sensor was also worn and corroded. Cleaned as best as I could. Found igniter worn with cracks starting. Found water in pressure switch tubing. Cleared drain lines. Found some obstruction. Ventor motor is worn. Rust damage behind Ventor motor found. Checked and adjusted gas pressures to maximize efficiency. System took 3 cycles to fire correctly. This is an indication of a possible short on main board. Preformed combustion test and found higher levels of CO in exhaust as well as elevated levels of XS air. This is a indication of blockage of secondary heat exchanger. Average life expectancy for this unit is 14 years. This unit is over 20 years old and in very poor condition. Due to age, condition, and cost of repair, second opi