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WRS321SDHZ Whirlpool Refrigerator - Anyone knowledgeable with how "Adaptive Defrost Controllers" works?


Premium Member
Jan 23, 2021
Model Number
Less than 1 year
This fridge was bought from a tent sale clearance new with some cosmetic damages. It was sold as is with no warranty.

The refrigerator operated fine for a month (used infrequently) and then I noticed that there was ice buildup on the evaporator coil. The defrost cycle was not coming on. Got into the service mode and I was manually able to activate the defrost cycle and saw the heater come on. This tells me the defrost control function, relay and wiring was OK then. The service sheet said the defrost heater should be about 600W, that translates to roughly 24 ohms. I measured my heater and found it to be 120 ohms and thus concluded that the heater was not getting hot enough to melt the ice during the allotted defrost cycle. I bought a new defrost heater and installed it. Several weeks later, found ice buildup again so the new defrost heater did not fix the problem.

I verified again that the service mode activates the defrost heater and it does. I verified that the defrost thermistor's resistance (2.7K@room) matches its sensed temperature when cold and it does. If you look at the attached schematic, there are no defrost timer or defrost thermostat, it's all microprocessor controlled. Running out of ideas, I bought a new controller board and swapped it. Still the same problem, no defrost cycle! I have put a data logger on the defrost heater and it never sees any voltages at all, that is to say that it is not shutting off prematurely.

I checked the freezer door switch in case the adaptive defrost controller is counting the number of door openings, the switch's no/nc contacts both work. I have run of ideas other than some wiring harness problems, even then, what wiring could be wrong?

Anyone knows in more details how the adaptive defrost controller looks for in terms of environmental conditions in order to trigger the defrost cycle? Thanks.


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Hi, we need the complete model number first, you missing some digits at the end, read it from the model number tag located inside the refrigerator section on the upper walls or ceiling.

Here's the results I get:

Adaptive defrost and will run a defrost cycle anywhere between 8-96 hours of compressor run time.


So I am wondering what other electrical signals the microcontroller is looking for to initiate the defrost? Both FC and RC are working fine, temperatures are in range.

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