Thank you for your question. I know it's frustrating when the refrigerator stops cooling. Unfortunately, without the model number, I will only be able to provide some general information. If the fan motor inside the freezer is running, the frost build up will probably be due to a faulty defrost system. As the frost builds, the air flow to the fridge section will be reduced. The information you have received is very good. I hope it will help you. If you would like more assistance, reply to this thread and please include the complete model and serial number and I will be glad to assist you further.