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How to test the thermistor

I have a whirlpool fridge model WRF560SEYM00. I was having defrost problems so I tested the heater, it’s good. But to test the thermistor I would need to strip it since I can’t see the plug. Wondering if anyone knows a better way to test it without making any “damage” to it. I’m also assuming I may have to replace the ADC and I don’t know where that is, is it behind the control housing on the top centre of the fridge? I’m have trouble getting it off and don’t want to snap anything. Thank you!

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@jayeff [image|2477883] [image|2477882]

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Hi @pinkdiamond ,

Couldn’t find a free service manual online but have found this where it can be purchased.

Usually the manual shows how to get into the diagnostic mode and test the R & F temp thermistors and also the defrost thermistor.

The manual should also have the wiring diagram to show where the defrost thermistor connects to the mainboard.

Alternatively, on some other models I’ve found that on the mainboard, that where the defrost thermistor wires are connected, was designated as evap therm and GND. Check the mainboard and see if yours may be the same. ( maybe P8 1 & 2 if there?)

If you can see the designation at the mainboard harness plug then disconnect the power to the refrigerator and unplug the connector and place an Ohmmeter between the evap therm wire and GND on the plug wires. You should get a reading. You would have to know the specifications of the thermsitor to know whether it had the correct resistance for the temperature at the time of measurement as they are an NTC type (negative temp co-effiicient) which means that as the temp goes up their resistance goes down. You could try heating it slightly and see if the resistance drops but unless you know the specs, this is the best that you can do, besides the fact that you know it connects to the mainboard OK.

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Hey @jayeff

Thanks for commenting

I have tried using the diagnostic mode last time this happened and followed everything correctly but I wasn’t sure what I was looking at, all the lights came on at the end and no lights ever blinked while checking everything. Maybe I’ll put the fridge back together and run the diagnostics test again. Going without a fridge has been dreadful lol.

* I’ve edited the post to add a photo of the diagnostic sheet.

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@pinkdiamond

Table 1 steps 7 & 8 are the thermister tests i.e. LED1-4 on and then off when complete and then I think that Table 2 shows if there is a problem with one of them e.g. evap therm = defrost thermister = LED5 only.

Presumably if you don't get LED 5 after LEDs 1-4 have turned on then off in Steps 7 and 8 then it is OK.

What is the actual defrost problem that you're having?

You said that you tested the heater, what did this entail? Heater element OK, power to the heater is OK?

Also did you check the drain tube from below the evap unit to the evap pan under the compartments, to make sure that it is not blocked preventing the defrost meltwater from draining away? Thereby backing up and refreezing inside freezer compartment and building up over time after every defrost cycle.

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@jayeff

Here’s my message from previous post

We purchased a used refrigerator almost a year ago & were told that we would need to unplug it once a year to thaw it because they’d ice up. They had a technician go to them 2 years prior who said he could change the board but no guarantees that they wouldn’t encounter this problem again. Anyway, it started a few weeks ago making that loud noise of the fan rubbing against ice. So I unplugged it, dusted the back of the unit and plugged it back in the next morning. It’s been 2 days now. I haven’t heard the noise but my fridge is warm and the freezer is cold, but not freezing anything & I have both on the highest setting. The back wall also has ice build up again but no noise yet, I tried to do that diagnostic tool thing before I unplugged it to see if it would tell me what’s causing this. I followed the instructions and all of the lights popped up like the say in the diagram but for the end result I got what I’m taking as multiple messages which mean nothing to me

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@jayeff

I haven’t checked the drain tube, will do that now. I’m not sure if you are able to check my previous questions but the back wall gets frosted over ( pics are included) I didn’t test the power to the heater just the heater itself, I unplugged it and tested the prongs in the plug with my meter

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@pinkdiamond

I looked at your previous post and I agree that it is a defrost problem.

The defrost cycle in your refrigerator is most probably controlled by the mainboard. It should stop both the compressor and evaporator fan approx. once every 8- 10 hours and turn on the heater to melt any ice build up on the evap unit. When the temp in the freezer reaches the set temp to end the defrost cycle as indicated by the defrost thermister, the control board will end the cycle and restart the compressor and the evaporator fan to cool both compartments back down to their respective set operating temps.

The defrost cycle should last approx. 20-25 minutes.

The evaporator fan drags the air across the evap. unit and this cold air is blown throughout both the refrigerator and freezer to cool them down. If the refrigerator is warm but the freezer is cold, most probably the ice build up is preventing the fan from operating correctly so no cold air is blown into the refrigerator but the freezer is cold because that's where the evap unit is.

Is the refrigerator staying off occasionally i.e. no compressor running, for a long while before restarting again? By a long while I mean 30+ minutes. If so it may be that if the heater is not working the temp in the freezer rises more slowly so less ice would be melted before the cycle is ended. The heater is there to speed thing up so that the food doesn’t thaw.

You would need to check that there is power going to the defrost heater during the defrost cycle and also check the drain tube.

If the heater circuit is OK then check that the refigerator does go into the defrost cycle. This may take a while as I’m not sure what the time duration is between cycles but it should be at least once every 8-10 hours and the compressor should not be running for the above mentioned time. If it does check how long it stays off for.

The diagnostics only prove that the components are working or not but they don’t actually check if the mainboard is implementing the cycles correctly etc, if you get my drift.

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Marissa sarà eternamente grato.
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