I think you are quite confused! Initially you talked about THE recirc fan (3/500)- the 400 has 2. Now you mention both!
I guess the recirc switches off because the flow is sufficient in high flow?
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The 'left pack controller' does NOT control the cabin..There are 2 Pack controls but 3 zone controls, none of which you mention.
Where do you get this thing about the 'left pack controller' controlling the cabin?