I know a bit about them and I've even had this problem before. There's a good chance that the evaporator fan isn't working. So, instead of evaporating, the moisture freezes. Run your a/c and if the compressor is running but the evap fan isn't, that's your problem. Check to see there isn't anything blocking it from working properly, be sure all your filters are cleaned, and you have good airflow to everything. Try to check this when it freezes up so you can see any ice buildup. Then, let it melt, and figure out what's causing it. If everything works well what's its melted, it's probably what I said above and possibly below.
There's also a chance the freon is low. Now, to many, that'll sound like the opposite problem, howver, low freon can cause it to freeze up. I won't get into the tecnnicalities here, but that's always a possibility.