I wrote "acc. TSM". Thats the Trouble Shooting Manual.
The values for the CL are the same.
Boeing said in the service letter 36-013-B that if inflight duct pressure is below the values mentioned above but more than 18 psig,
...the airplane can be operated normally (without imposing the MEL), but action should be taken to investigate and restore the bleed system performance to normal operation at a convenient opportunity when manpower and equipment is available.
@ FCS Explorer
Only the Indicator of the CL is AC operated (28V AC).
The Indicator of the NG is only supplied by 115V AC. But it is operated by 7V DC.