Miele KFN 14827 Fridge/Freezer – Suspected faulty evaporator sensor

[Jonathon Waterhouse]

Hi all,

I have read through many of the posts already for similar fridges, and want to say thanks to all the knowledgeable folks who are helping those in need. It is very appreciated!

On to my issue…

I have a Miele fridge/freezer (KFN 14827 SDE ed) that is having a problem keeping both the fridge and freezer cool at the same time. Most of the time it can keep the freezer at temp (-18c) but the fridge stays at room temperature. Sometimes though, after I disconnect and reconnect power, the fridge gets down to temp (3-4c) but the freezer won’t cool.

The compressor is working hard, hot to touch and is a little noisy, but I think this is just because it is constantly working hard to cool the fridge. It’s an Embraco VEMZ 9C. I checked the Ohms between each of the three start/run/common terminals and they all read about 18 Ohms. I checked the datasheet and I think it’s supposed to be about 16 +/- 8{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} but I read it while it was still quite warm. Anyway, I think the compressor is okay just overworked.

The air temperature sensors I think are reading the correct temperatures, judging by what shows on the display. And the fans in both compartments are spinning.

So I think it may be the evaporator temperature sensor. From other posts I understand it is a common problem in similar models. I thought it may also be the solenoid that redirects cooling between fridge freezer, but also think this is a more expensive fix if so and worth trying the sensor first.

So after all that I have a couple of questions:
1. Does my diagnosis sound right to those in the know?
2. Which part number would I be after to replace the evaporator temp sensor on this model?

Many thanks in advance!

Jon

[Tony R]

Hi Jon, check that the freezer has not become over iced, these units will direct maximum cooling to freezer and sacrifice the fridge if the coil because is iced up to maintain the frozen food, take out all the freezer drawers and see if you have any frost/ice on the rear panel.

[Jonathon Waterhouse]

Hi Tony, thanks for your reply.

Yes I can confirm I’ve fully defrosted it (a few times over the last couple of weeks) and have taken the back panel of the freezer off to check. Each time I turn it back on the problem occurs, usually only freezer gets cold after letting it run for a few days.

Update:
I’ve taken the PCB out of the back and measured the resistance over each of the four temperature sensors (pretty sure they’re the right ones anyway), and they all read between 4.5 – 4.7 kOhms at room temp (about 22 deg c.). Not sure if this can confirm or not whether they’re working properly.

Update 2:
Have just let the freezer cool again, same issue occurs. The freezer reports it is at the desired temp -18c, but the fridge stays at room temp. I’ve quickly unplugged it and measured the each of them temp sensors from the PCB. They are (from left to right, starting closest to the PCB side edge): 3.6kOhms, 3.6kOhms, 12kOhms and 12.3kOhms. I assume the last two are the freezer temp and evap sensors. Do they sound correct?

From this person’s account, it seems they might be accurate: https://www.ukwhitegoods.co.uk/forums/forum/public-support-forums/help-and-support/fridge-and-freezer-forum/91725-miele-kf7654-sne-temperature-sensors

[Jonathon Waterhouse]

Have checked the continuity across the defrost heating element, it measures 290ohms. When the freezer is at temp I’ve removed the back cover and can see some frost on the evaporator fins, but doesn’t ice up (although have only run it a few days at a time so far).

Also if the freezer is at the correct temp, and I turn the power off for a couple of minutes and then on again, the fridge then starts cooling down to 3-4c, but then the freezer starts cooling and fridge temp rises again. It’s like it gets “stuck” in freezer mode and never switches back to cooling the fridge. It can at least start cooling the fridge when I turn it on (and I think I can here the solenoid tick over when I turn it on), so I hope that means the solenoid is okay.

Might this point to an issue with the defrost cycle?

[Jonathon Waterhouse]

After checking everything else I could think of (and concluding they’re probably working correctly), I’m now worried I’ve got a refrigerant leak and/or a bad compressor.

I think there’s an abnormal frost pattern on the evaporator, the picture below was taken with freezer running for a couple of days and reporting it was -18c. There’s frost all the way along one line and none on the other and no frost on the evaporator itself, other than a little bit of ice under the frosted line where I think some water has dripped down during the defrost cycle and refrozen. From what I understand this can point to low refridgerant.

https://imgur.com/a/TUVmFeD

Since it still has some cooling performance is it worth getting someone to recharge the refidgerant (r600a)? Or any other diagnostic check I could do? Since it’s otherwise a good fridge I’d prefer to repair it if possible rather than throw it out.

[Tony R]

It certainly looks like a shortage of gas or a poorly pumping compressor, only a trained Engineer will be able to tell you which it is by doing a pressure test, compressor changes are expensive and a lack of gas would mean a hole somewhere in the system and unless found and repaired, if at all possible you will continue to lose gas as soon as it is refilled.

[Jonathon Waterhouse]

Sorry to revive an old thread, but Tony was right and it was a refrigerant leak. After much messing about I managed to find and repair the leak and recharge the fridge with refrigerant. It’s been running well now for a few weeks. The compressor is also running quietly again and only intermittently!

Some pics and a write up here, hope it might help others: https://www.wtrhs.com/article/miele-refrigerator-repair-leak/

Thanks so much for the help!

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