If the house didn't have air conditioning before, chances are good that having it now would increase the value. Nothing is guaranteed though, there's still a chance that you'll still sell for the same price. would suggest talking to a professional about it. If they can see the house, and if they know what it was worth before, they would be able to tell you what you can expect. Good luck with everything, hopefully this air conditioning addition will make things a bit easier for you.