What's wrong with my freezer?

[MadAlicesDad]

Firstly, apologies for the legth o fthe post. This is my first post and I'm not an expert on fridges, but hopefully someone reading this can help me!
On Thursday last week I had had an electrician check and connect a circuit I'd installed in my kitchen. At some point the power was turned off and he'd also done the RCD trip tests etc on the new circuit. Although the freezer is on a different circuit to the one being tested, in the process all the circuits in the house had been repeatedly powered up and tripped by the main RCD.

Later that evening I found a pool of water under our Kyoto (Iceland own-brand) KU96FF frost free freezer. The freezer power light and the red 'too warm' warning light were on. When I switched to fast freeze, that light came on too, but the compressor did not kick in.

I turned the power off for ten minutes and then turned it back on, still nothing.
I removed the front trim to access the PCB (see photo below - note the photo has been rotated 180deg so you can read the PCB) and checked the connectors were tight. When I disconnected the red plug (marked CON1), the fast freeze and warning light started to flash and the compressor kicked in. I reconnected the red plug and the compressor continued to run and the FF/warning lights stopped flashing and stayed on.
8592

I turned off the power, turned it back on and it didn't start; removing the red connector had no effect.
I turned the power off, left it a few mins, turned power on. It didn't start immediately but when I removed the red connector the compressor started and the FF/warning lights flashed as before. I reconnected the plug, the lights stayed on and compressor kept running.

I left it running, the low temp lamp went out after about 10 mins and it has carried on running since then. However, if the power gets cut, it needs the 'reboot' procedure to get it going again.

Can anyone suggest what the fault may be and/or why removing the red connector (or the white one I've since found out) once the power has been off for a few minutes makes it work? Is there a fix, or is the PCB damaged?


TIA Mike

[frank]

If its a frost free fridge, then, at power on, the defrost heaters come on first for a period, say 20 mins, before refrigeration starts, so you may not have a problem but may need to have patience.
I'm not an expert on domestics and I'm sure someone will be along soon with a better answer

[MadAlicesDad]

Thanks for the suggestion. It is frost free and patience was my initial approach (we had a similar problem after a powercut a few years ago). Unfortunately patience is not enough this time. At the weekend I turned the power off for another job, reconnected it shortly afterwards and forgot about the freezer. 2 hours later (and having opened the freezer a few times in that period) the red light was on again. Turn off, wait, turn on, remove red connector and it starts again!
Although I can't find the other ends of the wires I think the red and white connectors go to thermistors - resistance is around 20-36kOhm and seems to vary with temp of freezer.
I'm trying to work out the circuit diagram from the PCB but I suspect the IC has been damaged :(
Mike

[tonto33]

seems you have a faulty thermistor which needs replacing, pcb should be ok if you want you can send it to QER.BIZ who will test it for you

[MadAlicesDad]

Thanks for the suggestion - I'd found QER on the web, but sending the PCB away would mean I'd have to empty the freezer, plus there is no guarantee it would fix the fault. As the freezer still works, there's no urgency so I'd like to see if I can track the problem before sending for repair.

When you say thermistor are you talking about something that measures the temperature of the freezer or somewhere on the PCB? IIRC thermistors are sometimes used to limited power surges.

I think the red and white connectors go to thermistors buried inside the freezer, but I don't know where and I doubt if they are easily replaced. However the resistance of them is 35.3kOhm (red) 27.9kOhm (white) when the freezer is running normally and 56.7/40.5 when fast freeze has been on for 60 mins. Is this about right?

I've started to analyse the PCB and there is a component marked R2 within the part of the circuit that I think rectifies the 230VAC to DC. It's marked 05K25 0145 - googling suggests this is a varistor used to protect equipment against transient voltage spikes. Could this be something to do with the problem?

NB I'm a mechanical engineer so I'm outside my comfort zone here and all help is welcomed!
Cheers,
Mike