The Harbinger One instructions indicate that C20 and C22 are only necessary when using a 9V supply but not when using a 18V supply. Looking at the schematic, it seems like that should be C19 instead of C20. C19 and C22 are both part of the charge pump circuit and are not in the circuit when the charge pump is disconnected. C20, on the other hand, is a filter cap on the 18V node.
Just thought I'd mention it.