Hi all,
The aircon temp control on a Classic B747 is quite simple, the cabin is divided into 4 sections, plus the upper deck.
When the system is normal, in auto mode, the three aircon packs are controlled to provide conditioned air to all sections of the cabin at the temp that is required to keep the warmest section at the selected temperature. (ie, the coldest requirement)
Then, all the other sections add hot air as required to maintain their selected temperature.
So all the pack outlet temperatures will always be the same.
So, on the FEs panel, one of the five hot air additive valves, one to each section, will always be closed, indicating that is the section requiring the coolest conditioned air!
We even have recirculation fans to help 'mix' the cabin air.
Of course, in the 3-man cockpits, someone is always watching all the systems, and any slight adjustments can be made easily, just ask a crewmember, and they will pass the message on to the FE,
no problem!
The system works well, even at flight idle.
Did anyone hear of the B737-800 recently that had a double trip-off of the overheat control valves at TOD, (with the corresponding failure of the aircon/pressurization), and NOBODY noticed until the cabin altitude horn sounded on the way down, (with the cabin on the way UP), guess nobody was watching the shop!
Cheers