Fourteen inches is a full grown Chuckwalla. If you are keeping it at 89-95 degrees in the basking end of the cage, with a rock to hide under, that should be good. Your food choices are good, especially the dandelions--their favorite. Not sure why he doesn't feed. Can you post a picture? Is this lizard emaciated?
Have you tried setting it outside on a table in the direct sun to see if it will move around? Maybe it is injured? Does it walk? Need ore info!