AC Problems, Solutions?

two things cause icing. Low charge or low air flow/too cold. Low air flow is caused by plugged coils or grilles/filter; assume you've checked that from your post. Too cold air is caused by air short circuiting from the supply to the return as mentioned by Chris. when you remove both covers and see the blower look around and make sure all the baffles are in place and sealed, look for gaps where the air can get from one side of the blower to the other (short circuit). This is a VERY common problem. It's possible there's a low charge but doubtful, if there's a leak it will probably be flat and it wouldn't freeze up. You can check for obvious leaks by removing the outer cover and looking at the coils and pipe for oil.