Are you sure that your extract from the AMM is correct? My Vol 2 Systems manuals for the 3/4/500 and 700 all state that “AUTO - When operating one pack from APU (both engine bleed air switches OFF), regulates to high flow.”
I could only prove it correct by doing what you're going to do, S&L
... try it next time I'm on the aircraft.
Both the text and the Wiring Schematics seem to reflect the same thing. Also, the one pack scenario activates the same relay as the two engine bleed off scenario. Each provide an (different) earth/ground to energise the Norm(Low)/High relay.
Thanks for the tips on procedures, gents.... and I look forward to the test results.
Cheers.
Q.