C-hing, what you said seems make sense. The c-fu also said if he only drilled upon a neutral wire in such circumstances, I should buy the mark six.
My air conditioner has been in use for 7 years. It has been working well and actually it was not in use for only a month or so. It is a Panasonic split type air-con. There seems to be no reason for it to break down suddenly. Anyway, I agree that I should find an air-con c-fu to check it. Really hope that it is not necessary to dig the wall la.....because the wall is covered by wall paper and it is not possible to find the same wall paper now.