I decided to re-trace a journey I did 15 years ago by travelling south by train from Hualomphong station. I decided to treat myself and go by diesel rail car (DRC). It was a painful and uncomfortable trip due to the Antarctic conditions as a result of the air-conditioning, and the food and drink supplied was of a poor quality.
I'm not sure why the air-conditioning has to be set at such a low temperature but it was not a pleasant experience. On the return trip, I was a bit better prepared wearing a long-sleeve shirt and hat, but I could still have done with jeans, jacket, and a beanie!
One of the solutions was to stand at the end of the carriage near the connection to the next carriage, as this area was separated from the air-conditioned section by automotic doors, but this involved standing outside the smelly toilets!
A better option would be to use the 3rd class train which has windows that open.
Be warned! You need to be prepared for DRC!!!