The def. t-stat is a side issue. The frost pattern is a sign of a compressor not pumping the way it should or low on refrigerant. You can put gauges on the system to find out which, and add refrigerant if you want to, but the system only holds (usually) 4.5 oz. It doesn't take much of a leak to need to add more. If there is a leak you need to find the leak and fix it (very time consuming). That is why earlier in the post it was said to replace the fridge. If you are knowledgeable in refrigerant sealed systems, you know what to do from here (and have fun, I hate leakers) If you don't then the best fix is to replace the fridge because paying someone to do it will cost more than half the price of a new one.