A good central air conditioner should give you 15 to 20 years service. Repair or replacement depends on the extent of damage. Thanks to the durability of brick, most exterior masonry walls are good for many lifetimes. Re-grouting may be required after 40 years or so. They require particular attention to maintain their effectiveness, including spot repairs for leaks, condensation problems, and warping.
Home buyers can save future dollars by adopting two strategies.
One is simply to buy a new home with an insured warranty policy. A second strategy involves purchasing an existing home. If the home is 15 to 20 years old, negotiate the replacement or repair of those systems which are likely to fail in the near future before you buy.