Fixing a KGV3120GB/01

[fridgeowner]

My fridge/freezer developed the usual problem – still cools, but lets the temp go way too high before restarting – power off/on fixes it for one more cycle

Since some of the info has disappeared from the web, here’s what I found and did:

There are two sensor cables emerging from the foam going to the RH four pin connector.
The PCB is marked for four or three connections (one or two grounds)
Unplug the sensor plug
The slightly thicker cable is dark blue and dark brown – measures 16kohm each way, dropping quickly as it warmed (from about 4.8C) Looks like an NTC thermistor in good order
The thinner cable is light brown, light blue, and measure 300K one way, and the DMM wouldn’t stabilise the other. Weird – this is the broken frost sensor
Clip the thin cable, tape the fridge end, strip, join and tape the connector end – put another way, the frost sensor will now be zero ohms
Refit the sensor plug

Works great – thermostat now cycles 3.5 to 5.0 C – no ice buildup yet
WARNING The main switch contacts are bare – unplug before opening the control box, and do insulate your cut ends…

HTH

[dr_jonno]

Re: Fixing a KGV3120GB/01

My bosch kvg3120gb/01 seems to have the usual problem too – gets very warm (>0C in the freezer) before the compressor kicks in.
I have followed the threads about the fixes and found the information contradictory in many places.
Here is what I have found, and my reasoning. Hope it helps someone.

On this 4 wire connector there ARE small numbers (1 to 4) on the face where the wires go in. I have
1-light blue
2-dark blue
3-dark brown
4-light brown

unplug the connector (squeeze the clip to allow it to release). If you look at resistances between the pins on the circuit board with a multimeter, you’ll see zero ohms between the pins where the blue wires go. ie these are common, so must be ground. so the BLUE WIRES ARE GROUND.

I have seen the thermistors desctibed as NTC (nagative temp coefficient). THis means the resistance is high when cold, and goes down as they warm up. So when the modification talks about shorting two wires out (ie zero ohms), it is telling the control that the thermistor is WARM.

My reasoning says that if shorting the thermistor out is a working fix, then the contol board must think ‘if both thermistors are warm then put the compressor on’. In other words, the fix tells the control that one thermistor is always warm, and the compressor should come on when the other thermistor says ‘I’m warm’.

With the connector unplugged, I measured:
12k ohms between 4 and 2, light brown and dark blue
1M ohm, dropping to 30k ohms over 5 mins with the fridge door open between pins 1 and 3, light blue and dark blue.
So the fridge thermistor must be connected between pins 1 and 3.

Perhaps I should have waited longer with the door open to see if the fridge thermistor dropped any lower – the fix would suggest that this thermistor is unable to go below the value needed to make the control think the fridge is warm.
With the fridge thermistor changing, I dubious that this fix will work – I would expect a dead thermistor to be open circuit, ie very high resistance, but I figured I’ve nothing to loose. I’ve switched on and the compressor has kicked in so we’ll see.

What I am confused about is why the ‘fix’ seems to focus on just one thermistor. Surely either of them could be faulty? In which case you could short out either 1 and 3 (fridge) or 2 and 4 (freezer).

I would be very grateful if someone who knows what is going on could reply to some of these questions. Thanks

[fridgeowner]

Re: Fixing a KGV3120GB/01

If the two thermistors were for the fridge chamber and the freezer, then you’d be right.

Earlier posts suggested that they’re not – that the freezer is calculated to run below -18, and no worries if a lot below, and that the sensor are fridge temperature and rear cooling panel temp (in fridge). If the rear panel is too cool, then it must have ice on it, so switch off until the ice has melted. (This makes the machine ‘frost free’)

My fix lies to the machine, effectively saying there’s no ice. Over the last 9 months, I have had to defrost the rear panel twice – if you’re really careful setting the thermostat you can keep a decent temp and get any ice to melt (as long as the kids don’t let too much fresh damp air in constantly going in the fridge 🙂

I believe dark blue is the fridge device – I recall it changed by a few kohms as I worked. This is about what you’d expect for a few C change on an NTC. (I’ve looked at an NTC datasheet – expect about 25{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} change between 0C and 5C)

[smartin]

Re: Fixing a KGV3120GB/01

strange how you reply straight away to a problem with exactly the same machine after 9 months and yet still only 2 posts :rolls:

[dr_jonno]

Re: Fixing a KGV3120GB/01

I’m happy to report that the fix did work. The temp control dial does now do something again – ie turn it up and the compressor kicks in.
The fridge and freezer seems to be at healthy temperatures.
I would agree that it makes most sense that there are two sensors in the fridge. HOWEVER, with the fridge door open I only saw one sensor resistance drop. This was the one I shorted out and I assume is in the insulation at the back…. If the other sensor were also in the fridge I would have expected to see it change too.
If anyone knows for sure where these sensors are I’d be interested to hear.
Thanks

[nomadPaul]

Re: Fixing a KGV3120GB/01

dr_jonno wrote:I’m happy to report that the fix did work. The temp control dial does now do something again – ie turn it up and the compressor kicks in.
The fridge and freezer seems to be at healthy temperatures.
I would agree that it makes most sense that there are two sensors in the fridge. HOWEVER, with the fridge door open I only saw one sensor resistance drop. This was the one I shorted out and I assume is in the insulation at the back…. If the other sensor were also in the fridge I would have expected to see it change too.
If anyone knows for sure where these sensors are I’d be interested to hear.
Thanks

They are inside the insulation in the rear wall of the freezer IIRC….hence the inability the actually replace the thermistor , just work a way round it with the modification.

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