Dell 2135cn - Multifunction Color Laser Printer Troubleshooting Manual page 202

NOTICE: To avoid irregular screen image or malfunctioning of your printer, avoid placing the printer in direct sunlight with the single sheet feeder
opened.
Provide enough room to open the printer tray, covers, and optional equipment. It is also important to ensure that there is enough space around the printer for
proper ventilation.
Automatic Document Feeder (ADF)
1 ADF Cover
2 Document Guides
3 Document Glass
4 Document Feeder Tray
Operator Panel
For details on the operator panel, see
Protecting Your Printer
To protect your printer from theft, you can use the optional Kensington lock.
Attach the Kensington lock to the security slot of your printer.
"Operator Panel".