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Re: Beko CDA543FW-2 fridge freezer air sensor replacement
Right, apologies for missing some queries and personal messages from ages ago. I will try and answer best I can but I don’t have the appliance here now so will have to go by memory. It still works fine btw.
Earlybird66 – I think I dug to the right of the pcb housing, maybe slightly lower rather than higher, but really not sure. I don’t know to what extent a temperature gradient forms across the rear panel (freezer to fridge) and thus how precise the vertical position has to be. You ask how deep – well very deep – all the way to the metal rear panel – I wrote about the importance of good thermal contact. Just dig out the foam with a scalpel; I don’t see you can do much harm. You don’t need to physically locate and remove the old sensor, and the nearer to the pcb housing the easier it is to route the sensor cable to KN3. Somewhere on this forum someone else has posted photos.
To Bekobeko – sorry I don’t know or can’t remember, but these are NTC types, so resistance will rise as temperature falls. WRT which thermistor did I use, I might be on very dodgy ground here but if I remember rightly there are only two sensors sold for this appliance by Whitegoods. One is a temperature switch (closed or open) and I think helps control auto defrost and the other is an NTC thermistor for temperature control. Again going by memory (and I could be very wrong) the freezer incorporates both parts whilst the fridge employs the same NTC sensor (only) buried in the foam and connecting to KN3. The interesting question is how do the two NTC sensors work together. I suggested a possibility in my previous post. I surmise that the freezer NTC sensor is the master.
To Washdisher – I don’t think I had the correct plug so I cut the wires from the existing sensor (which I never found and hence left in situ) and soldered in the new sensor instead.
To answer your personal message re how sure am I that the appliance will work with KN3 disconnected (i.e. open circuit infinite and impedance as per my last post), well not at all! The sensor is there for a reason and my tongue in cheek observation was based upon a very short period of time so I certainly would not recommend it!If anyone knows how the two sensors operate in conjunction with each other I would be interested to hear.
Finally pleased be warned I am a just competent (I hope) professional analogue engineer and not in any respect trained on appliances.
Re: Beko CDA543FW-2 fridge freezer air sensor replacement
I am now able to give a solution to the problem with my Beko CF6914. The fault found is almost certainly that which numerous other owners of this model (and similar ones including the one entitling this thread) have been trying to find. Firstly let me say that there is a lot of poor, misleading and just plain wrong advise out there which leads you in the wrong direction, so beware, and perhaps beware of what I am saying also!
I asked earlier where KN3 cabling was routed – well the answer is, I believe, to a fridge sensor buried somewhere within the foam insulation on the rear of the fridge. The clue was that the KN3 cabling presented an impedance of about 11k at ambient, rising (but fluctuating indicating a fault) with decreasing temperature, suggesting termination with an NTC thermistor. Some further searching on line revealed that burying sensors within the potted insulation is standard practise with Beko and certain other manufacturers – great!
My method was to dig away some insulation behind the fridge, quite near to the main pcb and install a new sensor (I think Beko use the same one as in the freezer) in the space formed. I used thermally conductive adhesive (and a piece of carefully shaped tin wrapped around the sensor to improve thermal contact) to glue the sensor to the rear surface metal of the fridge. The sensor cable was carefully routed through the potting and through a small hole I drilled in the plastic pcb holder then connected to KN3. Expanding foam was used to make good the missing insulation and further secure the sensor. I am pleased to say that the appliance now runs with the fridge and freezer on around 4 and -18 degrees C respectively, so success I think.
Tbh it is hard to see exactly what the fridge sensor actually does given that there is no independent regulation of the fridge temperature – as I understand it the fridge is cooled due to its thermal mass being in close proximity to that of the freezer and an equilibrium or temperature gradient results. There is no air ducting. I would guess that the controller looks at both sensors (freezer and fridge) and tries to alleviate over temperature should a door on either be left open. This would of course force one or the other to go under temperature but this presumably is preferable from a food safety consideration. Interestingly the appliance appears to work ok with the fridge sensor removed altogether (pull out the plug on KN3). This means that probably the controller is programmed to completely ignore the sensor input when the impedance read on KN3 is infinity. Thus no sensor is better than a faulty sensor!
Finally, there seems to be quite a few folk pulling there hair out over this over cooling issue so maybe Whitegoods might like to say why both they and other professional appliance forum moderators usually never mention the existence of the fridge sensor – presumably they do know about it!?
Re: Beko CDA543FW-2 fridge freezer air sensor replacement
I have an identical problem on a Beko CF6914 (which appears identical from the photos), where the freezer fails to regulate and the temperature gets far too cold.
I think you are confusing the auxiliary pcb in the top of fridge compartment with the main control pcb sited in a compartment on the rear top of the appliance. The former just comprises a potentiometer which feeds a small change in resistance to the main pcb when the temperature dial is adjusted. As stated there is no air temperature sensor as such, although strangely the replacement part is often called this. On my unit I have replaced both the sensors and the main pcb, and have checked out the auxiliary pcb, yet still the fault persists. I have checked the wiring wrt to the main sensor (the top one) and the aux pcb to the main pcb and all is good. The sensors check out fine too. So what is wrong on these Beko appliances? I am tempted to suggest a wiring fault somewhere in the foam – but how and why – it seems unlikely? Or is the replacement pcb faulty perhaps? I do not have a wiring diagram and am puzzled as to the source/destination of the orange/grey pair connected to socket KN3 on the main pcb, Would have expected these to connect to the lower sensor (temperature switch) but they do not – so where do they go, and where does the sensor switch route to if not the main pcb? Is there a further controller somewhere perhaps? Am tempted now to hack away the foam on the rear to get to the wiring but can anyone put me out of my misery first please? Am I missing something? Thanks.
