Much like some office buildings or universities state a range of acceptable temperatures to set the thermostat at, some subway systems have similar philosophy. You might see these stickers on the subway exit doors explaining the temperature range they aim for in summer and winter. The left shows summer and aims for a temperature between 18C and 20 C. The right shows winter and aims for a temperature between 26C and 28C. Image taken in Daejeon.

While Korea is a homogeneous society, not everyone has the same body type. Some people get cold easier than others, and other people run higher body temperatures. During the summer and winter months, this is an issue as people can have very different opinions on the appropriate temperature to set air conditioners or heaters and the range of temperatures, as shown above, sometimes just doesn't feel right for the season. After enough people complained to train conductors, some lines started to run cars at different temperatures. This is not year round, and this is not every rail system, so it may be difficult to know if the line you frequently use goes by this system.

To let people know that one car is 2C hotter or colder than the others, a large sticker will be placed inside the corresponding vehicles. The location is above one of the long middle benches in the main section of the car. There may or may not be English. This image was taken in the Seoul system.