I travelled on 197046 last week, and whilst the air con and ventilation was running and maintaining a reasonable temperature, it sounded quite unhealthy.
Firstly, the overhead fans would blow for about ten seconds, cut out for three seconds, and then blow again. This continued for the entire journey.
Secondly, there was a loud motor, which I can only describe as sounding like an industrial lathe, spinning up and slowing down periodically underneath the floor.
Thirdly, the vibrations from the engine when idling were quite bad.
As an aside, what is with the ugly "food area" taking up so much space on a two car train?!