samsuks fridg

[SIZE=3]I have read a lot of complaints about samsung refridgerators. I will join the long list of un happy consumers. The large upper refridgerator side builds up ice on the cooling coils behind the pannel. repairman replaced sensor and fan 7 months ago. It just recently froze up again and gave false temp readings. Had to remove back panel and put blow dryer on it for two hours to melt ice encased coils. It is doing ok now. What is causing the freeze up? [/SIZE]