Barry B Orlando , FL January 17, 2016 Appliance: Whirlpool Refrigerator WRS526SIAH00 Whirlpool Refrigerator Wrs526siah00: Bimetallic switch intermittently not working defroster heater would not melt frost when bimetallic switch did not close. How to replace Refrigerator Defrost Thermostat. Replaced bimetallic switch and refrigerator has been working for more than a week correctly maintaining freezer and refrigerator temperatures. So, frost is being melted and air flow is not being blocked. It was very surprising that failed switch would be intermittent. 15 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 2+ hours