Also re: Overground air-conditioning it really doesn't factor in humidity. And in the morning I think the problem is like a car, the air conditioning only fully comes on when the engine is under load. So when it sits at Crystal Palace and runs to Brockley, because the stations are so close and it's been sitting at Crystal Palace, the engine rarely gets going. After New Cross Gate it starts to come on. But by then it's too late and you get off anyway.
On the way home it's usually Ok because it's been running since Highbury.