It wasn't bad, just felt stuffy. They fixed it very quickly and the cabin steward even checked back a few hours later to make sure everything was working ok. Of course, when we first reported it, they asked if we were sure we'd closed the balcony door. Yes, we did. 🙂 The AC will shut off if the door isn't closed properly. Also, keep your drapes closed during the day to keep the heat out. That glass door got hot!