It would be great if we could give you a definitive answer, like 25 years, but realistically, air conditioner life expectancy will vary a lot over several years. A central air conditioning system usually lasts 15 to 20 years before it needs to be replaced, but in some cases, it may need to be replaced sooner. Just because it keeps working doesn't mean you should keep using it; inefficiency can be a major expense on its own. For this reason, most HVAC technicians will recommend replacing any HVAC system that is 15 to 20 years old with a newer, more efficient model.
If a technician recommends that you replace your HVAC system with a newer model, it may be worth getting a second opinion, if only for your peace of mind. And when a major problem occurs, the decision to repair or replace the air conditioner can add years of comfort by replacing an important component.
