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I have a whirlpool top-mount refrigerator (WRT138TFYS) that is about 4 years old. The motor will kick on as the temperature in the fridge rises, but once it starts running it will not turn off. If we let it go the temperature in the refrigerator compartment will drop below freezing. The motor will keep running until I manually turn the thermostat to 'off'. I can then turn the thermostat back up to our preferred setting and the motor will stay off until the temperature rises again.
I had a repair technician take a look and he could not find anything obviously wrong with the refrigerator. He thought the condenser might be going as the coils were not getting very warm. Based on what was happening with the motor he thought it could be the thermostat or control board that needed replacing.
I purchased a used thermostat and installed it last night. The fridge is still behaving in exactly the same way.
As I see it there are two possibilities:
1) Control board needs to be replaced
2) The used thermostat I bought happens to be malfunctioning in exactly the same way as the original.
I would appreciate any thoughts or opinions on this issue. We actually just sold our house before this problem appeared and I really don't want to pour any more money into a relatively low-end appliance that is going to belong to someone else in two months. The control board is fairly expensive (over $200CAN) so at that point I would be approaching the cost of a replacement used fridge in repair costs.
Thanks.
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If you want to diagnose this you'll need a multimeter and a basic knowledge of electrical terms. one of 2 things if happening.
1) The thermostat is failing to tell the board that it is satisfied. The used thermostat complicates that issue. When it reaches set point it should open the circuit through it. Meaning no continuity if the machine is unplugged and the thermostat is checked very quickly.
2) The board is failing to turn open the relay that shuts the compressor down during defrost. When it is too cold in the fridge you may be able to tap on the blue box on the control that contains the relay with something nonconductive and break the contact free, if so it's that board. I'd need a wiring diagram to be more specific and am not finding one at the moment.
If you're up to opening the control area and exposing the thermostat, do so and then let it run until it should have shut off. Then unplug the unit and quickly check for continuity between the 2 terminals on the thermostat back. If there is no continuity the thermostat is satisfied and the board is your likely problem.
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Originally Posted by: PNWDrew  If you want to diagnose this you'll need a multimeter and a basic knowledge of electrical terms. one of 2 things if happening.
1) The thermostat is failing to tell the board that it is satisfied. The used thermostat complicates that issue. When it reaches set point it should open the circuit through it. Meaning no continuity if the machine is unplugged and the thermostat is checked very quickly.
2) The board is failing to turn open the relay that shuts the compressor down during defrost. When it is too cold in the fridge you may be able to tap on the blue box on the control that contains the relay with something nonconductive and break the contact free, if so it's that board. I'd need a wiring diagram to be more specific and am not finding one at the moment.
If you're up to opening the control area and exposing the thermostat, do so and then let it run until it should have shut off. Then unplug the unit and quickly check for continuity between the 2 terminals on the thermostat back. If there is no continuity the thermostat is satisfied and the board is your likely problem. Thanks for the advice. I am attempting to perform the test that you outlined but it is proving a bit more difficult than anticipated (the fridge is taking exceptionally long to get to temperature now, I'm worried we may be burning out the compressor since it runs so often now). In any event, I was thinking about what you wrote and had a question. Does the fact that I can get the compressor to turn off by turning the thermostat to the "off" position not suggest that the relay on the board is opening properly? In other words, can the board differentiate the open circuit from the thermostat arising because the temperature reaches the set points vs. an open circuit caused by turning the thermostat to off?
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I'd lean toward the thermostat since it does turn it all the way off. It is the more likely suspect. If you decide to replace it take pics off the probe routing unless you have a very good memory. And be gentle with the probe it is a hollow pressurized tube and can kink or break. Do reuse any sheathing on it. It insulates the probe to decrease the effects of quick temp variations from door openings.
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Rank: Member
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Originally Posted by: PNWDrew I'd lean toward the thermostat since it does turn it all the way off. It is the more likely suspect. If you decide to replace it take pics off the probe routing unless you have a very good memory. And be gentle with the probe it is a hollow pressurized tube and can kink or break. Do reuse any sheathing on it. It insulates the probe to decrease the effects of quick temp variations from door openings. I actually already replaced the thermostat once - but it was a used part. So I was able to do the test you suggested. Even when the temperature is lower than what I think the setpoint should be I have continuity across the terminals. However I can turn the thermostat to 'off' and I lose continuity. I can then turn the thermostat back up to the previous setpoint and the circuit remains open until the temperature gets high enough inside the fridge compartment. So for some reason if the circuit is closed (i.e. compressor 'on') the thermostat is not able to open the circuit based on temperature. However it will open if you turn the thermostat to 'off'. Then the circuit remains open even if you turn the thermostat back on and set it to the previous setpoint. This sounds like a problem with the thermostat to me, however both the used thermostat I bought and installed and the original thermostat that was in the fridge are behaving in exactly the same way. It seems unlikely that both would be broken in the same way.
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Yes I'm often concerned when symptoms don't change also, we get "rebuilt" parts sometimes and it leaves you unsure of what to trust. The probe part of the thermostat is actually a tube. If it looses pressure it'll behave similar as described.
Inside that thermostat is a baffle or diaphragm that feels the pressure and opens or closes the contacts as needed. Those contacts can stick together, the off position forces them apart.
I'll take a few minutes later to look at your wiring diagram as see if any other ideas make sense
Often people notice that a tap or other impact to the thermostat when it is too cold will open it. Try that perhaps if you haven't. It's low tech but pretty definitive.
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