Hope someone can help me here! I have to sell a customer on the fact that their hvac system is at or approacing "THE END". The bean counters are not so concerned with the technical aspects of their broken down and inefficent old system, but more concerned with how long the average system lasts. Does anyone know where there is some "PUBLISHED LITERATURE" concerning the life expectancy of hvac equipment. This paticular equipment is a 30 year old Carrier split system (20 ton). Economizers' are disconnected, compressor unloaders don't work, Acid in oil, etc. This equip. is ready to go. They don't want to put the money in it to polish it up, and don't want to spend the money to replace it.