it appears that the photo black is empty even tho the display shows 2/3 full!?
Most missing nozzles are not clogs, and if you lose a full channel, it definitely isn't a result of clogs, its the result of no ink getting to the head. Although very
rare, but I have heard cartridges running dry but showing not empty because of a chip fault on the cartridge.
As mentioned, a complete channel drop is normally not a head problem, nor is it a clog problem, but a damper/air problem. The damper is designed to bleed air as it gets to the head to avoid nozzle skips.
If the cartridge has indeed run dry, then it will take some time to purge the air. I think you are better purging it with cleaning cycles, not with trying to print black.
I hope ammonia hasn't killed your head however .... based on the symptoms, soaking won't help at all, and ammonia can ruin the delicate internals of the head, although the 79/9900 heads seem to be more sensitive than the other printers to windex/ammonia.