When is the best time to replace an AC? For equipment older than 15 years, waiting too long to replace could mean the equipment breaks when you need it most. This leads to expensive emergency service calls and limited equipment replacement options. To avoid that stress, expense, and lack of options, make a replacement plan beforehand. Before you decide on swapping in another standard AC unit, consider the benefits of upgrading to a high-efficiency, cold-climate rated air source heat pump.