It is their home. Not trying to be harsh, but its not your home and you are a guest. I'm currently working in a home that is really hot. They have a/c, but can't afford to make it cooler. They let a nurse go that opened the windows because it was letting the little bit of a/c they use right out the window. There is a fan in the room. What you consider hot, others may consider comfortable. The patient has probably been in that hot environment for a very long time and probably way before you got there. They are probably used to it. What did people ever do before a/c?
I will take my patient outside sometimes just to cool off and give her a change of scenery. I also put my drinks in the freezer to make them like a slushy so it helps cool me off. I wear my thinner scrubs
too. I've also begun keeping my house a little warmer and not relying on a/c in the car as heavily so the heat doesn't shock my body as much when I get to work. I know construction workers that leave their windows open year round and they get used to the extremes in temp so it doesn't bother them as much at work.
You can't control them, but you can control your own actions. If you still can't tolerate it, they will find a nurse that can. Nobody lives the same way you do. If you were in an office with a locked thermostat, you couldn't do anything about that either. I just read an article a few days ago that said most of those thermostats in the offices are fake to make people think they are changing the temp.
I've seen nurses get let go in the past for changing the families thermostat. Again, its their home. I NEVER touch a thermostat unless the family specifically asks me to and gives me a temp or range of temps that I can change it to. I will also remind families that some of the equipment puts off a lot of heat and makes the room warmer. Sometimes they'll offer to provide additional fans.