Beko CFP1691W Fridge/Freezer Malfunction

Thanks for the quick response, Dave. The compressor runs, then stops, apparently when the fridge temperature has reached its set-point. Fyi (you may already know), for this model there is no separate temperature control knob for the freezer.
Btw, I didn’t mention in my first post that there were a lot of strange wheezing sounds coming from the fridge freezer around the time I noticed the freezer wasn’t as cold as it should be. May be a coincidence though, because yesterday (7th Aug) was hot, even in Manchester.

Thanks Dave. Your help is much appreciated. As you said there are 2 plugs. Looking at the stuffed side of the PCB, there’s a 5 pin plug top right labelled KN2 on the board. To the left, a 2 pin plug labelled KN3.
For the 2 pin plug (grey and orange wires), initial resistance was very close to 20kohm. By the time I had taken other measurements, resistance had dropped to 18.6.kohm. I estimate the fridge temperature had risen by a couple of degrees over that time, to ~5degC. Hopefully those are close to expected values.
The 5 pin plug was a little more complicated. The are 4 wires attached. Fom the RHS: grey / empty / black / brown / red.
The resistance between grey and black was very close to the 2 pin value when measurements were made straight after each other; ie. ~18.5kohm. So, assuming the fridge and the freezer really were at roughly the same temperature – then the freezer sensor appears to be working OK ?
I took resistance readings of all the other wire combinations on the 5 pin plug; the only pair that wasn’t open circuit was red / brown, which gave a reading of 38.6 kohm at the time when the grey/ black measured 18.5 kohm.. Any thoughts on that ?
Btw, I’m still trying to understand how a single compressor and a single temperature controller can control different zones (ie. fridge and freezer) to widely different temperatures. Some cunning valving system ?

Re. compressor switching: if compressor is off, and I leave the fridge door open to warm it, after 30-60secs, the compressor switches on. Then it runs until the fridge is cooled sufficiently, then switches off. It’s as if the electronics is ignoring, or unaware of, the freezer.
Probably not significant, but even when the fridge and freezer are at room temperature, the compressor has never switched straight on after plugging into the mains. There’s always been a delay of a minute or two.
I’m still puzzled as to how cooling is diverted from the freezer to the fridge ? There must be something that causes the cooling system to switch to the fridge when the freezer has reached its set temperature (of approx -18degC). Maybe the malfunction is in this section ?
Unfortunately, I can’t get back to the unit for a few days now, so won’t be able to make any more tests until then. Still very interested in getting this problem sorted out though.
Cheers

OK, thanks. When I get back to the unit, I’ll take some resistance readings whilst adjusting the temperature control knob, to try to understand where and how temperature control set points for fridge and freezer are fed into the PCB. Maybe the fault is with the freezer set point ? Failing that, I could buy and try another PCB. The consensus seems to be that fridge/freezer PCB’s are pretty reliable though.. Last resort, I could call out a fridge/freezer engineer, and hope it can be fixed at a reasonable price. The unit isn’t yet 2 years old, so I don’t want to give up on it..
One last thing for now: is there a simple equation linking thermistor resistance and temperature, that I could plug into Excel, or perhaps a look-up table available to the public ? You seemed to be using such a reference source earlier in this correspondence. When I looked on-line for this info, there seemed to be a lot of different thermistors in fridge / freezers, with presumably different sensitivities.
Thanks again.

Some developments since your (Dave) last post:
– Making a log plot of the data from your table between +10C to -25C gave a close fit to the following linear equation: temperature = ( -18.67 x ln (thermistor resistance)) + 65.24.
– In my absence, the freezer section was reported to be behaving ‘normally’ again. So I took some more thermistor measurements, and used the above equation to calculate the temperatures. I also used an IR temperature gun to get some direct temperature measurements, to cross-check.

With the temperature contoller in the fridge set to mid point (setting ‘3’), I got the following results:
– The two pin plug (KN3) gave a resistance of 32.3 kohm, equivalent to a temperature of 0.4degC. The IR gun aimed at the back of the fridge behind the chiller box showed 2-3degC; so, pretty good correlation.
– The five pin plug (KN2), between the red and brown wires, when measured twice at different times (and therefore at different parts of the cooling cycle) gave resistances of 80 kohm ( -16.6degC) and 114 kohm (-23degC).
An IR gun reading taken at the rear of the top freezer shelf was -16degC. So, (a) pretty good correlation again and (b) the freezer section did indeed appear to behaving itself.
.
You may recall that I previously measured a resistance of ~18.5 kohm between the grey and black wires on the 5-pin plug, and thought that could be the freezer temperature. Well I got almost exactly the same reading again when the freezer was apparently much colder, so the 1st assumption was incorrect.
It transpired that the grey-black wire resistance was coming from the temperature controller: At settings Min, 1, 2, 3, 4, Max , resistances were respectively approx. 50, 40, 30, 20, 10 and 0 kohm. These values must somehow be converted by the PCB into reference values for the fridge and freezer thermistors.

So, all making sense now – except I still don’t know what was happening when the freezer wasn’t cooling sufficiently ! As I said at the start of this post, it had been a hot day, and there were some strange wheezing noises coming from the unit. Maybe there was some sort of blockage in the cooling system, as you suggested. Fingers crossed it doesn’t happen again.
Thanks for your assistance.