In MAN mode, what happens when the DUMP button is pressed?

When the DUMP button is pressed in MAN mode, the most immediate effect is that the packs and recirculation fans turn off. This function is integral to the cabin pressure and environmental control system. By shutting down the packs, which are responsible for heating and cooling the cabin air, and the recirculation fans, which help redistribute that air, the aircraft's systems prioritize an emergency decompression scenario. The DUMP function is specifically designed to facilitate the rapid decrease in cabin altitude in the event of an emergency, ensuring that the pressure in the aircraft can drop to ambient levels quickly, allowing for safe egress of the cabin environment.

In this context, turning off the packs and recirc fans is a crucial step that aligns with the goal of reducing cabin pressure to stabilizing atmospheric conditions, rather than actively increasing pressure or maintaining it at operational levels.