God, They are still doing this? I got told exactly the same thing many years ago (when I travelled public transport regularly) and was shocked to be told that they had to get a specialist in to turn it off. Who the heck designs a vehicle with a huge design flaw like that?

I have always found the Northern Line to be hot and stuffy. The people in charge of the underground once released a statement that said it was too HOT to have AC in all the carriages!