I used to joke that I had a "rat thermometer" - when it was cool, the girls could be found curled up on the bottom level of their cage, but when it was hot, they would rise to the top (I always assumed to get closer to the a/C vent). I fussed and worried over them, always running the heat or a/C more for their benefit than mine.
Zephyr seems immune to the heat or cold. Neither seems to affect his behavior much.
But poor Zipper. He really, REALLY doesn't like the heat. Poor little guy.
For the record - I turned on the A/C on May 26th this year. I was trying to make it to June but temperatures inside the trailer topped out the thermometer and even the open windows and fans couldn't keep up.