Because this is a recurring process that does not seem simple enough within ACDSee, this is a quick how-to Isolate the "A" sides of the photos, after the blank "B" sides have been deleted.

Despite having the "correct" folder selected on the left-hand panel in the tree; you need to look for the folder on the right titled "Categories and Folders". Use the folder selection titled: "In any of the following (1) folders:" Note if the program is filling up the page, or the right column is too narrow you may not be able to see the full path of the folder. This is critical especially if you don't Add the exact folder and neglect to "check" the "Include sub-folders" box.
Also you need to put "*A.jpg" into the "Search for diles or folders named:" spot above in the section entitled "Files and Text". Now this part seems (to me at least) to be opposite of where it should go, as the next spot is entitled: "With the text:" So make sure to put that in the right spot!