Until and unless your air conditioner is breaking down really often and has some expensive repairs, you do not need to replace your AC every 5 years. I dont know where you found that information but air conditioner replacement can be expensive. For example, you are buying a brand new air conditioner and it would be unwise to do so if you dont really need to replace your current system. Most air conditioners work perfecly fine for 10 to 12 years, provided they have had regular maintenance and tuneups. I am a contractor, and I have done numerous replacement. But I have yet to have an air conditioner that needed a replacement in 5 years. If you think your air conditioner is proving to expensive due to the regular repairs, then yes, you do need to look for a new system in the market.