yachtno1,
You will have no a/c from the eng driven gens - I think the underspeed switch takes them off line about 45%N3/N2. There will be none from the APU - illegal, even if it is being used to supply air. That leaves a teeny weeny bit from the stand by a/c for a few must haves.
Cornish Jack,
The cut in pressures are of academic interest only when there is no air or a/c to drive them.