How long to keep an old a/c
The initial cost of replacing your AC unit is high, but that doesn’t mean you should avoid a new purchase. Don’t make the mistake of keeping your old air conditioner long than you should. An old air conditioner will perform poorly, cost you more money in repairs and eventually become more trouble than it’s worth.
If your AC unit is 15 to 19 years old or older, investing in a newer, more efficient version will save you money and aggravation over time. If it's 20 you need a new one asap..