If the temperature is not to your liking, mention it to the attendant, and he/she may be able to do something about it. Of course, be considerate of your fellow passengers as well. One recent summer evening, my family boarded #2 in LAX to ride home. We has just left the station and got settled in to our beds when it suddenly started to feel warmer. After a minute, I could detect the telltale smell of heater running, and checked the vents to find warm air blowing out. I immediately jumped out of bed and threw my clothes on to run upstairs to find the attendant.
"Something's wrong!", I said. "The heater started running!" He replied, "Oh yeah, I just turned it on. One of the passengers said she was cold." My jaw dropped. It was 80 degrees out when we left LAX a few minutes prior. I thought there had been some mechanical failure. I've always been nice and respectful to all the Amtrak staff, but this was the closest I've come to letting someone really have it. I told him "With all due respect to that passenger, if she's cold, that's what blankets are for. I was already down to my underwear downstairs before you turned the heat on, and I can't take off anymore. She can put on another blanket. I can't take off my skin." As I was starting to say this, another passenger came barging down the upstairs hall looking for the attendant and wondering out loud what was going on with the heat. The SCA could quickly see that he had caused a problem and was about to face an unruly mob, so he went right downstairs and switched it back.
So, moral of the story: if you ever have to decide between pleasing those who are always too hot and those who are always too cold, keep the temp colder and make sure the cold people get blankets.