The fan system installed when new, without opening windows was inadequate to ventilate the cars in warm weather.
There were several instances of people fainting in the trains when they were first introduced.
Complaints from train crews about the noisy fresh air fans immediately behind the cab were also raised.
A trial was performed using car 7108 which had hopper openers fitted and also slots above the windows which could be opened/closed from inside:
1980s car ventilation experiment using large grilles above saloon windows
flic.kr
During investigation it was found the hottest part of the car was immediately behind the drivers cab, so a compromise was made. The window had a small hopper added to the top but as the cab door slides into the pocket it couldn’t be made full width.
Only unit 7129 the last built, was fitted new with the modifications. All other units were modified either (back) at Metro-Cammell (single-ended) or Acton Works (double-ended).
The modified fan system made the end-car fresh air (noisy fans) to only run on batteries when traction current was discharged. The axial car fans had their angle changed by tilting the grille to offer a conflicting blast of air in the centre of the car. New extractor fans were placed towards the centre of the car, requiring roof panels to be replaced with large slots in them.
The trial car 7108 had the exterior above window slots plated over, as these weren’t found necessary and gave a problem in where to place the interior car line diagrams.
Driving Motor Car 7108, formerly used for ventilation experiments
flic.kr
