If you dispatch a B737NG with the, say, right pack inop (max FL250). Then during cruise the left engine fails. QRH says to turn Left Pack OFF. Question: In this case the isolation valve should be open, due to dispatch with right pack OFF. In flight, will/can the Bleed Air from the no. 2 engine be used by the Left Pack to maintain pressurization, which in turn means you should NOT turn the left pack OFF? Should you manually move the isolation valve switch to OPEN, or just leave it in AUTO?
Can the APU maintain pressurization if you descent to FL170 and turn the left pack ON, and in this case, in what position should the isolation valve switch be in?
Can't get my head around this. All good inputs are appreciated.
