Vidal G Leesburg , FL April 26, 2018 Appliance: Whirlpool Refrigerator WRF736SDAM12 Whirlpool Refrigerator Wrf736sdam12: The freezer was building ice in the coil causing the fridge to warm up. How to replace Defrost Heater. I replaced the Bi-metal-Def and the heater, but it didn't fix the problem ,so I replaced the control board and then it worked. 6 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 30-60 minutes