I bought my Charleston in Nov 2014.....
And I have had the same problems....here is what I have been told:
- the valve is not positioning or switching properly(however, when I took to Freightliner, they did not agree)
-it takes a while for the bags to "inflate"...although there may be a leak or a fitting not secure.
When I have this problem, I turn the engine on and off, recycle the leveling system.....and the turn the engine on. You can tell the difference in the height the tire is below the fender.....
Good luck, and let me know if you find out something else!!