@Jean118 I think you haven't gotten a flood of answers here because this is a tough one to enforce. Sure, you can come up with some wording to the effect that the place isn't suitable for guests who are going to be hanging out all day in the unit, but that that doesn't mean that guests won't book and hang out all day anyway. There's been plenty of hosts report that their guests indicated that they were coming to explore the area, do a lot of hiking, visit museums, etc, but in fact ended up almost never went out at all, just stayed on the couch watching Netflix for days on end.
I see you have 2 entire house listings and one private room listing, so I'm assuming this issue is for one of the entire house listings, because if it's a private room where you live, you could regulate the AC use more.
Honestly, it seems to me that the only fool-proof method is to either upgrade the AC units, which you say you can't afford right now, or up your price to cover repairs to the unit you have now so if guests don't follow the guidelines and overuse it and cause issues, you can afford to have it serviced.
I simply don't have AC at all in my house, even though it's really hot and humid where I live for about 4-5 months. I have really good ceiling fans and some stand-up fans as well. But I don't get a lot of bookings during those months either. Not only is it down season for tourism in this beach town, if people do come, they usually want a place with AC and a pool. The few guests I do get in the hot months have been fine with the fan, but I tend to get seasoned travellers, who've endured much more uncomfortable scenarios in places they've travelled, and are adaptable, rather than guests who require everything to be exactly perfect.