I might be missing something obvious, but maybe this is a bug?
I made a simple pneumatic
Engine → Pack → Cabin
Engine → HotAirValve →Cabin
Engine → VacuumOutlet
(I tried this with a junction after the engine and feeding everything from there, made no difference)
Now the strangest thing is, if the pack if OFF, the engine’s bleed air output in the lines drop to environment pressure. In the Engine section in the ECS debug window it still shows the proper pressure, but every line coming out from the engine does not receive it. So much so that the Vacuum stops working and there is no heat going into the cabin at all from the valve.