What do roof blisters do? How come GE Jersey Arrows have shorter ones?
Air conditioning?
The roof blister in this case has the resistors for propulsion system and a few fans to cool them.
on RDC’s and such it contains the radiators and AC condensor plus the fans to cool them
keeps thems babies cool
On NJT MU cars, the resistors are for dynamic braking. In this mode, the traction motors become generators and the electricity they produce is sent through the resistors to put a load on them, thus slowing down the train. It makes the train stop in a shorter distance, and saves wear on the brake shoes. The Septa cars in the pic probably have AC gear up there too, that’s why they’re longer (my guess, anyway).