Any domestic refrigeration engineers in the house?

I have a technical query on my Bosch upright freezer and would really like a chat with a domestic refrigeration engineer to check my fault finding results. A circuit diagram of the cabinet wiring and sensors for a GSU3401GB/52 would be really helpful.
Reward would be considered as I'm am close to being at the end of my tether.
TIA
Bob
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Bob Minchin wrote:

Okay, and I might regret replying. It has been 19 years since I repaired refrigeration. How old is it and what is it doing?
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Mr Pounder Esquire wrote:

It is possibly about 10 years old. I bought it second hand about 8 years ago and it has worked flawlessly until last October when it froze up. The problem is in the return lead from the defrost heater. The switched live on the heater is driven by a triac and is working - it switches on every 12 hrs and 42 minutes for about 32 minutes. The compressor switches off for that period via another triac. The return lead from the heater goes via a 2 pin connector into the case wiring and the other pin on that connector goes to neutral. As far as I can measure, the two pins on that connector have >20Mohms and so not current ever passes through the defrost heater element (which measures about 290 ohms) which makes it designed for about 200 watts output.
Whatever this two pin connector is for I cannot find it on the spare parts listing. The overall effect is that over about 3 months the evaporator freezes up solid and needs 24hrs or more to thaw meaning we have to move everything out into a chest freezer.
Thanks for your offer of help but I possibly need someone who is used to working on these new(ish) computer controlled freezers. The older motor driven clock motor type defrost timers were so much easier and simpler to understand.
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Bob Minchin wrote:

Frost free are shit. Too much to go wrong. The older units with a simple thermostat ran until the compressor packed in or the insulation failed. The very cheap Zanussi standby freezer in the garage gets used every Xmas and it must be 15 years old. Insulation is shagged, but it still works. I'm sorry I can't help you. If you give up, please buy a conventional freezer.
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Mr Pounder Esquire wrote:

Thanks for replying. I cannot agree. This frost free machine has been perfect for years. Now something has gone wrong and I'm trying to analyse the fault, replace or modify it so that it continues to be (near) perfect again. I have two conventional freezers and defrosting is a PITA
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Bob Minchin wrote:

I defrost the freezer compartment in our conventional fridge freezer every 3 months. It takes 20 minutes using a hair drier. This gives me the opportunity to give it a clean and chuck away any food that has been there for too long. I do not regard this as being a PITA. Frost free has: timer, stat. defrost heater, fan PCB etc and all of the stuff that you are having problems with. Sensor!? My conventional only has a stat to go wrong. ?12 off the net and dead easy to fit. Apart from refrigerant leaks and compressor failure, that is all to go wrong. I hope you get your problem sorted.
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Mr Pounder Esquire wrote:

The mystery component has been identified as a thermal fuse and is on order. Meanwhile a jury rigged solution with a cartridge fuse is under test whilst a pc logs the behaviour for analysis in the morning. Well on the way to a solution I think.
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Bob Minchin wrote:

Well done and I hope it works.
https://www.youtube.com/watch?v=ztABYog5x3o

https://www.currys.co.uk/gbuk/household-appliances/refrigeration/freezers/333_3128_30215_xx_xx/xx-criteria.html
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On Sunday, 21 January 2018 21:03:40 UTC, Bob Minchin wrote:

So you know a connector is bad, what do you want?
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snipped-for-privacy@gmail.com wrote:

I don't think the connector is bad. I want to know what is on the other end of it and what its function is. Logically is should be some sort of a switch, fuse or a temperature operated switch. It has to pass the defrost heater current around 1 amp So before I just short it out, I'd rather know what it is supposed to do and assess the risks of bypassing it.
So what I want is in the subject line. First hand experience on the principles used in this product and therefore to understand why the heater element is not simply returned to neutral.
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On 22/01/2018 07:42, Bob Minchin wrote:

There is a post on UK Whitegoods that references a thermal fuse for the defrost heater. That post says it is pushed into the evaporator fins.
Post also says it it not shown on exploded parts list but they give the number as 00617855.
A search on this part shows a thermal fuse terminating in a white 2 pin plug/socket...
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Lee wrote:

Lee, You are a star. Thank you
Although I had searched UKwhite goods forum, nothing came up for my model number but as you say there are other results that point to my problem once I search for thermal fuse. A post there also explained another observation in that a secondary heater in the drain tray also stays on for a further 10 mins after the main heater goes off. This not on explains my logged behaviour data but explains the fourth triac switch on the control board. Triac current ratings and function below These are 16 amp Compressor on/off. 7 amp Defrost main heater on off 1 amp drain tray hearer on/off 1 amp air circulating fan on/off
If you would like to mail me direct with a paypal account address or similar I would be very happy to provide a drink for you in return for your help.
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On 22/01/2018 14:16, Bob Minchin wrote:

I'm just pleased to have helped in some small way. That's what this place has always been about and long may it continue!
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Lee wrote:

You have been a great help Lee and I am very grateful. A jury rigged solution is under test as I write and the thermal fuse is on order. Bob
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