Probably best to select media (paper) source tray on the basis of a combination of Paper Size (e.g. A4, Letter) and Paper Type (e.g. Plain, Letterhead) rather than selecting a particular physical tray via its identifier.
With many printers (including the LJ Pro 400 series):
- The printer should know what size of paper is in each of the cassette trays, via sensors connected to the paper guides within the trays;
- The size for the multipurpose tray 1 will probably have to be set via front panel menus or the Embedded Web Serverequivalent; there are special settings for tray 1 (e.g. type = any to always use it if it is open);
- The type of paper in each tray will have to be set via front panel menus or the EWS.
Then within the Print dialogue for a print request, you have to select the appropriate combination of size and type, to match the settings in the printer.