Makes no difference anyway. In absence of any bleed air pressure (i.e. engines OFF and APU bleed air switches in OFF position), the pack valves will not open anyway when the PACK switches are moved to AUTO, since they are pneumatically operated.
In the preflight procedure, Boeing recommends a “top down approach”: packs first, then isolation valve, then engine bleeds, then the APU.
Air conditioning PACK switches – AUTO or HIGH
ISOLATION VALVE switch – OPEN
Engine BLEED air switches – ON
APU BLEED air switch – ON
Verify that the DUAL BLEED light is illuminated.