My window Arctic King isn't removing moisture. No

I've been looking for your manual but so far, not luck. I'll keep looking.
If unit runs for long periods of time, it very well could freeze up. Unit will dehumidify any air that is blown over the cooling coil (evap).
Does your unit drip water while it is running? If not, it may be low on freon. Has it ever worked right? I am assuming it is a window unit and not a "Thru the wall" type.
The parent company is Midea-American. Their web site offer virtually nothing but sales pitches. Big waste of time. They work with Toshiba and Carrier but don't know to what extent.
I suggest running the unit one day with the damper in one position and the next day run it in the other position and see if there is any real difference.

Hope this is of some help. Good luck and I'll keep looking.