Cut the mangos into thin slices, about ¼" thick. You want the slices to be as similar in size and thickness as possible so that they all dry at the same rate.
Place the mango pieces on the tray of a dehydrator. Make sure to leave room around each slice so that the air can circulate them. You can sprinkle with sugar or lemon juice if desired, but it's not necessary.
Place the lid on the dehydrator and set it to 135ºF. It will take anywhere from 6-10 hours for the mangos to fully dehydrate. Start checking them around 6 hours. You want them to be just a little rubbery but not wet. I prefer my dried mango to be pliable and not completely crisp so I usually stop the drying at 6 hours. They will firm up a bit more once they cool. You may need to remove some smaller pieces first and keep dehydrating any larger pieces a little longer.
Store the dried mango pieces in a sealable container in a cool dark place or freeze them for later.
To prevent the mango pieces from sticking to your dehydrator, flip them over after 4 hours. This will loosen them from the rack and also air in even drying
Once done, the mangos should be pliable with no moisture present. Cut one in half, if there is still moisture, keep drying the mango until no moisture appears
Times will vary depending on how thin the slices are, the climate, the outside and inside temperature at the time, and your dehydrator.
Always read the manual for your dehydrator and follow all safety recommendations.