The answer to 'when to replace air conditioner' is that you generally need to replace your air conditioner every 10-15 years, or sooner if it starts experiencing frequent breakdowns, can't keep up with cooling demand, or becomes very inefficient. As air conditioners age, they become less reliable and use more energy, costing you more on your utility bills.
Factors like climate, usage, and maintenance can impact the lifespan of an AC unit. Units in hot climates that run constantly may only last 8-10 years, while those in milder climates can potentially last 15-20 years with proper care. Regular tune-ups and maintenance can also extend the life of an AC system.