Thetford Fridge/Freezer N3000 Series...problems

[DalmoreSteve]

It's the original fridge installed, we've had for 2 years with no problems. Tried to turn it on just before Xmas to use as an "over-flow" for excess stores, it wasn't happy. The LCD display flashed for an instant and has been completely "dead" since with no display of any sort, also no signs of life from the back of the fridge. I used a multimeter to check power yesterday, both 12V and 240V supplies are live and reaching the Control Board/unit fitted on the back of the fridge, also gas supply is available for it.
So I think the problem is most likely to do with the electronic control unit, or with the LCD control unit on the front of the fridge. Both parts are available on eBay, the Control unit is around £150, LCD less (don't recall), and I feel okay fitting myself but not sure which to start with.
Does anyone have experience of how to identify which unit to start with, or any other advise?
Thanks, Steve.

 

[dbnosey]

Have you tested the fuse in the control box at the back of the fridge. Bit of a struggle to get to, as its on the other side of the circuit board when you remove the control box off the back of the fridge.
Colin

 

[DalmoreSteve]

Hi Colin. No, I haven't removed the "black box" at the back of the fridge yet. I was hoping there was a fuse somewhere that might be the cause, but couldn't see one, so assumed no one would be daft enough to design a fridge you had to dismantle, to get at one!! That's great to know, I have my fingers crossed, it'll save me £150 at least, if the cause of my problem.
If the rain holds off tomorrow, I plan to disconnect this control unit. I'll let you know the outcome.
Thanks, Steve.

 

[dbnosey]

If you search on the internet you will find a article for fault finding on this fridge. As regards to the design of the control panel that was my feelings exactly. Good luck.

 

[autorouter]

I'm sure you are aware that there are two separate 12V supplies to the fridge. The power to the 12V element is separate from the power to the control board, and will be on different fuses.

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[DalmoreSteve]

Hi Autorouter. Sorry I'm ignorant on this. I can't see a second 12V supply anywhere around the fridge, other than that connected to the Control Unit. I've now got the control unit off and the electrical control board separated from the unit. There are labelled spade connectors for:- ENG Run, 12V supply, 240V supply and 12V Heater and 240V heater circuits; so the Control Box seems at the heart of everything, including power to the heating elements. My units a Thetford model N3145 could yours be different?

 

[DalmoreSteve]

Hi Colin. Fuses are okay, both 12V/20A and 240V/2A; Dam!!! The board looks clean, no signs of overheating or dry joints. A little bit of rust around the clip on earth terminals, but a screw joins these as well, so doubting this will have had any effect, so cleaned and refitted.
I'm coming round to thinking the problem might be with the LCD display/control board. I'm online trying to figure out how to get this apart; don't want to damage the plastic fascia. As I'm not getting any error codes (or display), as the online sites all point too, either the Control Unit is not delivering 12V to drive it, or the LCD unit is screwed. Until this morning, we didn't realise that there are batteries in the LCD unit, none had been fitted; maybe this has caused a problem?
I noted that the replacement units on line are a kit with both Control Box and LCD Unit combined at £145. Once I've checked the LCD unit, and found there is no obvious problem , this will be the route I'll have to go down.

 

[dbnosey]

Hope this helps
Colin

 

[dbnosey]

Might be better

 

[autorouter]

There's a 'permanent' 12V supply for the control board, so it can run everything including the gas side of things, even when the habitation 12V is switched off. The power to the 12V element is usually thick wire all the way back to the starter battery, with a 20A fuse on it. It's controlled by a relay and is normally only ON when the engine is running, and OFF when the engine stops.

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[DalmoreSteve]

Hi Autorouter, there are heavy duty 12V cables supplying the Control Box, and heavy duty 12v cables leaving it, heading to the heater coil. I can't actually see the wiring at the coil, to exclude additional cables? But my display is "dead", so the problem most likely lies between the Control Box and LCD display/Control.
Steve

 

[DalmoreSteve]

Thanks for wiring diagram Colin

 

[autorouter]

According to the wiring diagram there is a separate terminal '12VDC-LC+' which is the supply for the microcontroller (uC). There is a 1.1A fuse. This supply also goes (after the fuse) to the Display Module (DM). I'd be looking for and checking that 1.1A fuse. I notice this fuse is resettable. (pushbutton?)

 

[DalmoreSteve]

Hi Autorouter. Yes, I checked that fuse and its okay. There is no reset button on the board; there might be up at the front LCD display, but this is "dead". I've ordered a kit containing both replacement Control Box and LCD Kit and hoping this will solve things.
Steve

 

[DalmoreSteve]

Sorry for the long silence. I've now fixed the fridge...it was a fuse!
In more detail, I ordered new replacement Control Box/Board and separate LCD board/display from a dealer on eBay, allegedly to fit our fridge model number. I installed the Control Box/Board first, nothing changed...no display or lights. The new LCD board/display was the wrong unit; our unit had the LCD display hard soldered onto the board, the unit supplied lacked the LCD display completely, so we had to wait for the correct unit to be sent....the dealer apologised and did not want the wrong unit returned! Anyway, when this arrived and was fitted it made no difference, still no "life" on the display or operation from the fridge.
I started from scratch again with a multimeter and soon found the problem, in the loom for the fridge there is a 5A spade fuse (automotive type), I had only done a visual inspection of this (twice) previously and it looked okay, it wasn't. Although the fuse section had not burned out, current was not flowing...corrosion; it's very exposed, effectively directly behind the external grill in our installation. Changing this fuse brought some "life" to the display, Fault Code 12 .... "LCD Board and Control Board cannot communicate with each other"! At this point we had both new units fitted on the fridge and no matter what we tried, we still had the same problem, no communication. The only solution/combination that would work correctly was to use both of the original units again...fridge is back to normal 12V/240V/LPG all fine.
What "threw me" (apart from inexperience) was that there are two permanent 12V feeds to the fridge control board, a heavy duty 20A for the heating coil and 5A for the electronic/logic circuits. Because I was picking up 12V on the main board, I was assuming all was okay....dumb.
I'm not convinced that the replacement units we received were the correct ones....but they were not the cause of the problem. Worth noting for anyone in a similar situation, is that the Main Board (Control Box) looked identical, with all the same connections, except the 240V mains connection is now via two "spade connectors"; the original had soldered tracks on the board and a custom connector for this. A replacement cable with 90 degree female spade connectors is included in the kit and needs to be fitted. So the original 240V connector needs cutting off and new cable fitted.
I hope my experience here might be useful to someone else down the line.
Thanks everyone.

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[autorouter]

Great to hear you have it fixed. You're not the first to be thrown by the two separate 12V supplies - or a fuse that looks OK but doesn't actually let the current through. Usually the heater element supply comes from the starter battery (ie alternator) and the control box supply comes from the leisure battery.

 

[SnJ]

DalmoreSteve
I know you said it was in the loom but where was the 5amp fuse actually located???

 

[DalmoreSteve]

Hi. There was only 1 fuse in the loom and this was 20 amp automotive type, this must be to drive the 12V heating coils in the cooling unit. In my installation, there is no 5 amp fuse in the fridge loom, however my wife spotted online, a lot of motorhomers commenting about their fridge being on the same circuit/fuse as the radio...I was sceptical, but lo and behold, mine was as well! The fuse I am referring to is in the main Ducato fuse board; this is located at the dashboard, about level with the driver's right-hand knee, behind a panel retained by 4 screws. There's 22 fuses arranged in 3 rows, the radio's on the top left hand one from memory...check this one first if you are having problems (your radio would not function if it'd blown). We downloaded a fuse diagram from the web. Mine was 5 amp and okay, but the online details say it should be 10 amp? My fridge went off when I removed this.
There is another 5 amp fuse on the fridge (not in cable loom), this is not easy to check, it's on the circuit board running the fridge (there is also a 20 amp fuse on this board). To check these you need to find and remove the control unit at the back of the fridge... there's a lot of discussion about this at the start of this thread... remember to disconnect your mains electricity before "diving" in here.
Hope this helps.

 

[Preveli]

Hi Steve, I'm having a similar problem. On the control unit/lcd board at the on/off switch just a very weak green blink. At the power unit there is 13v going into the print board. So now I'm confused about your writing. You did check the power unit and you also had 13v despite a weak fuse in the car?
I've an identical fridge and changed the power unit. But still all the same. I want to change the control unit but the plastic looks like glued so I can't disconnect any cables. Is there a trick to open this unit? Thanks.