I think regardless of where you live, ambient temperatures or not, you need a thermostat and humidity gage. When you take an animal out of its natural environment and keep it in captivity you are responsible for replicating that environment as closely as possible. You can't do that if you have no idea what the temp is of that enclosure. So what if it is 90 degrees outside. What if he has his enclosure sitting near a stove or furnace causing the air inside the enclosure to rise above 100 degrees fahrenheit and stay that way all day? He could be slowly cooking his snake and not even know it, and why? Because he has no way of monitoring the temperature inside the enclosure. Whether this guy lives in a tropic climate or a freezing one he needs to have some kind of mechanism telling him what the temp and humidity is in the enclosure.

As for big breeders not using heat sources, hides, etc? I am well aware of that, however, they also have climate controlled facilities, and large breeder racks that are designed to keep the tubs in darkness to make the balls feel secure. That is a totally different situation than having a ball python in a solitary plastic container with no hide, no heat source, and no way to monitor the environment inside the enclosure. End of story.

Now moving on to the OP problem. Lets give him the benefit of the doubt and say his temps and humidity are fine. Then either something is wrong with the rats he's feeding his snake (and one every two weeks is not enough), or the snake has a medical condition and needs to be taken to the vet. Again, usually when a ball goes off feed it is because something is wrong with its environment, and how can he know whether the environment is stable if he has no temp gauge? Where I live it is always 10 degrees hotter inside than out, and some rooms, depending on which way they are facing, are upwards of 20 degrees hotter than outside without AC. His geographic location has nothing to do with whether or not his temps are healthy for his snake.