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Silverwings

Strange Fridge Problem

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Hi everyone, 

 

Been viewing the forums for a long time, but first time posting.  

 

Got a strange issue with my Thetford N3000 Fridge. It works OK on Gas, not had the opportunity to test on 12V from the car, but the main problem is on 240V.

 

So on 240V, the black pipework at the back behind the plastic grills gets red hot (like to hot to touch) so the heating element is 100% working. Problem is that the fridge does not cool at all.  

 

On Gas it cools OK, so the coolant system must work.  

 

Running a short EHU from the house and it's drawing the correct amps and watts inline with the fridge specification sticker when tested with an energy consumption monitor. Plenty of spare capacity in EHU amps too, so I can run the electric heating in caravan with no problems. Thermostat checks out ok too, with a continuity check and resistance changes with temp variation.  

 

Any ideas?? Should the pipe work get too hot to touch? 

 

Thanks 

Edited by Silverwings

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The pipework should be too hot to touch along the length of the flue vertical pipe and the top 1/3rd of the top horizontal matrix pipework, slowly reducing the lower you feel, until almost cold at the bottom prior to entering the heating area once again.  

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Thanks for the reply Brecon. Yes that info is great, and it seems that the heater is working OK, with the temperatures that you suggest in the pipework. Just odd that it's not cooling like it does on gas!

 

I've put the caravan heating on over night to make sure that it doesn't need more of a differential from outside to in, as the caravan ambient temperature is about 9 degrees.  

Edited by Silverwings

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A couple of things come to mind, both unrelated to whether it is on gas or electric, but could be mistaken for this:-

1. Level, caravan fridges can be intolerant of being out of level.

2. They can also be intolerant of overcooling from outside which is why winter covers for the vents are available and Thetford recommend them when outside temperature drops to 8°C.

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How long did you leave it on electric?  

My fridge cools  VERY slowly on electric, especially if empty. .  consequently I take some old plastic 2L bottles of water and ice blocks out of my home fridge and put into the caravan fridge to help it along. . Then take  out water and put in food just as we are about to leave. .

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OK, thanks got the tips, I have some vent covers so I'll try those and see if it makes a difference, and load it up with some cool freezer blocks. Caravan is within one degree level, but for fault finding I'll make sure it's 100% level.  

 

Also, got the ambient temperature inside the caravan to a toasty 20 degrees, which made no difference, the fridge just matched the ambient temp.  

 

Really odd how it works on gas but not electric, even though its obvious the elec heater is working. As an experiment, cooled it with gas and then flipped over to electric at which point it defrosted.

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Little bit more info, after 12 hours on gas the temp in the freezer is -18 and working perfectly, pipes at back are hot but can hold the top for a couple of seconds. Switched over to 240V, and all it would have to do is maintain the coolness, but 12 hours later the freezer is +24 and the black pipes at the back of the fridge are too hot to touch.  

 

Does this sound like a blockage, or more of a PCB problem? Or something else? 

 

Thanks 

Edited by Silverwings

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10 minutes ago, Silverwings said:

Little bit more info, after 12 hours on gas the temp in the freezer is -18 and working perfectly, pipes at back are hot but can hold the top for a couple of seconds. Switched over to 240V, and all it would have to do is maintain the coolness, but 12 hours later the freezer is +24 and the black pipes at the back of the fridge are too hot to touch.  

 

Does this sound like a blockage, or more of a PCB problem? Or something else? 

 

Thanks 

It sounds truly weird, you seem to have eliminated all the variables, proved that the unit itself is fully functional and established that the electric element is OK. Has me foxed!

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5 minutes ago, Stevan said:

Has me foxed!

You and me both! Haha! Thanks for the input you gave me previously.  

 

Searching online and through forums I can't find a similar problem. Almost like the 240v side of things is either over powering (PCB problem) or over heating due to a blockage and causing an overheat.

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I made my fridge like an airing cupboard by accidentally running electric and gas together. I'm guessing the fridge thermostat may be faulty and the element isn't switching off when it should. Too much energy is going into the system and it can't cope. Not very scientific but . ..

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Thank you all for your assistance 

Another small update. ... 

 

Resistance across thermostat in fridge at ambient temp is 12,000 ohms (12kΩ) 

 

Resistance across 240V heater is 230 ohms - 153 Watt heater

 

Resistance across 12V heater is 1. 03ohms.   140 Watt heater

 

All look good? 

 

Based on my quick maths, think the 240V, it's a little low on ohms. ... 

240x240/153W is 376ohms

Edited by Silverwings

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when we first had our caravan the fridge stopped working on 240 and the engineer fitted a new element and said all ok as it's heating up. Next time out still not working on 240 so another engineer came out on site and really tested everything and it was the main board.  

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Thanks Joanie, it may well be that. However the resistance on my heater is incorrect, only 230 ohms, and according to the attached flow cart its outside allowable range (312-380ohms) . New heater on order and I'll report back soon.  

 

With a lower resistance but the same voltage, the current and power would be higher, causing the overheating. Fingers crossed my fix is the solution 🤞

 

 

Screenshot_20181018-182745.png

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Pleased to report that the new heater has fixed the problem! Fingers crossed it now has years of reliable service🤞

 

Heater replacement was a relatively straightforward DIY, and didn't need to remove the fridge from the caravan or disconnect gas.  

 

I'm not sure if the old heater was the incorrect one, or if it had half failed into a lower resistance (higher temp) state, however it was outside the minimum and maximum figures given above. New one was 318 ohms vs 230 ohms.  

 

One last thing to share is the resistance tables for the 623077 thermistor, I was able to check that the values were correct for the given temp.

 

 

Screenshot_20181021-080553.png

Edited by Silverwings
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it's so good when some one who has had a problem  comes back to say that they've not only fixed it but how they fixed it.   

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