Does any -400 expert here know whether this also applies to the 744's APU too? In other words does the APU bleed valve switch have to be on for the APU to receive anti-ice protection?
Dunno about the 'expert' bit BUT....
The 744 APU does not have an A/I valve like the classic does. Also the APU bleed air valve is normally left in the 'ON' position but opens and closes as a function of the APU operation.
Same for the 777 too!