What if a tenant in Florida refuses to use AC?
Does the lease stipulated that they are required to use the AC? If not there is nothing you can do. If you want them to be using AC so that the place is less exposed to the humidity and other elements; maybe
offer to pay for the difference in electricity usage for the AC? I would presume the reason they aren’t using it is because of the expense. Again unless the lease requires it…there’s not much you can do.