Since they did offer you a room with a king bed (which unfortunately had some maintenance issues), I'm doubtful you will be able to successfully invoke the Plat room type guarantee. You can try though and see if the hotel management will give you the money, but I'm guessing it will be an uphill battle (and one you probably won't win.)

If you do go down the path of trying, the best approach I can think of is that they most likely knew the A/C is out in that room (unless it just now broke or AZ has been very cool recently with no one using their A/C) and they still gave it to you, one of Marriott's "best" customers knowing you very likely wouldn't like it. Of course it may also depend on what the room temp really is (i.e. sitting at 65 but you are trying to get it down to 60 or sitting at 80 and it won't go down any...)