@Julio-A13 Yes, that would be considered an emergency situation, but you can't just go in when the guests are out- you need to contact them if you need to do that. They might prefer to be there when you come over and that is better for you, too, so they can't accuse you of stealing something.
And if this is something that happens on some regular basis, rather than just something that might happen once every 2 years, you should mention it in your listing. If guests book a place that says it has AC, only to find they can't use it, they are likely to demand some refund and leave a bad review.