Do not know the model off hand, but it could be to do with a fan, if auto defrost, could be defrost heater not working, so will just continue to ice up. the fan would get blocked with ice and stop, which then makes it all worse. would suggest 1st, manually defrost it, you might then be able to hear any fan, unless it has had it, but will not know until defrosted, If fan on, then auto defrost heater not working, with unit unplugged, inside, back panel, will come out, behind, 2 coils, 1 is the evaporator, the other is the heater, the heater will be plugged in, so you can unplug it and check if open cct with meter, also look for a thermal fuse attached to it, that might be open cct. after that, a thermistor attached to the evaporator coils, reading from that varies, other than that, back to control circuit.
SD, February 2012