My freezer started to frost on the back cover panel of the freezer. The fridge was getting warmer. I removed panel and coils were froze solid. Tool my blow heater and got rid of the ice, so i could see the wires. Unplugged the heater plug inside the panel. Removed the heater wires and did a Ohms check. Found the bottom heater was burned, checked top heater it was good. This system of heaters run in series so if one burns out the other will not work. Ordered heaters and replaced them and problem solved.
Good Luck Ron