Should I Repair Or Replace My Air Conditioning?
How Do I Know When To Repair Or Replace?
"An air conditioner should last about 15 years. If a system that’s more than a decade old begins to falter, consider total replacement of inside and outside units rather than a major repair. Usually only one of the system’s major components—coil or compressor—fails, but it’s usually more cost-effective to replace the whole system at once. Unmatched major components can compromise efficiency and lead to added repairs.”
--1999 Consumer’s Reports Buying Guide, Central Cooling Systems, page 143