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.
HOA can demand their rules be followed at any time. Before you bought the house, there should have been an inspection and any HOA violations noted. Sounds like that didn't happen. You should have also had an opportunity to review the HOA bylaws before you purchased. Most people don't read them, so are surprised by stuff like this.
Since it's been "long after the home has changed hands" I'd definitely take this up with the HOA and find out why they've suddenly decided to enforce. If it's stupid, see if you can campaign to have the requirement changed. Usually HOAs are run by voting parties, attend the next monthly meeting and feel it out.... more