I've always heard that after ten years, you can start expecting things to go wrong with a house.
Sure enough, at ten years old, my A/C started leaking freon.
The rusted coils on the inside of an air conditioning unit. It's a side view at about 45 degrees with two arrays of the end of coils forming a V in the middle of the frame. Thing tubes come in from the left side of the frame and connect to the bottom of the V.
The radiator (shown here) had rusted to the point where a few pin hole leaks developed. Patching and plugging the holes is possible. That wouldnn't stop more from forming though.
It was at this point that I discovered the regulations on freon have changed and, because of that, they no longer make replacement coils for my A/C. The net result: I'm now the proud ownder of an entirely new A/C. Thankfully, I was ready for the expense.
I've been doing my own version of Dave Ramsey's Financial Baby Steps since college. Every month, my bank automatically transfers a little money into an "Emergency Fund" account. I don't touch this account unless I run into an unexpected expense that I can't otherwise cover. Like, say, needing a new A/C.
If you don't already have an emergency fund, I highly recommend setting one up with an automatic transfer. Like contributing to your retirement, very soon after you setup the automatic transfer, you'll adjust and won't miss it at all. It doesn't have to be much. $50/month will net you $1,200 after two years. Just a little longer and you'll be able to replace an A/C without having to go into (or further into) debt.