re: Replacing entire AC system

The minimum standard is 14 seer. With your system being 12 years old, you have a R22 system that will have to be replaced at some point. The price of R22 is going through the roof as the supply has been reduced.

I suggest finding a contractor that will come in your home and give you an air flow analysis to determine tonnage and whether there are any issues with your duct work. The majority of issues that people have are a result of air flow problems and homes not properly insulated. You probably need a 3 or 3.5 ton system. A changeout from old to new should not cost you more than $7k installed.

I also recommend checking into a 2 stage system should you have the extra money. They are work the money and will save you monthly.