Thetford N97 Fridge getting hot on 12volts

[Lazy-Ferret]

Can anyone answer where I need to look to find out why my caravan fridge actually heats up when on 12V.

When on either Mains electric, or Gas, it is super efficient, often freezing the contents of both the fridge and the freezer section, if we do not pay attention.

Ever since we have had the van, we have thought there was an issue with the 12v not keeping the fridge cool, but because of the way the car was set up, with 13pin socket, and the caravan with 2x7pin, with a converter lead, I blamed that to start. A few weeks back, I sorted all that out, but found that when connected to the car, the engine revs needed to be raised in order to get the volts up enough to turn the voltage sensing relay for the fridge to pull in, and this therefore needed 2 people to test.

After a quick test, when my wife was available, I was pleased to see that the blue light stopped flashing, and the number 10 fault code disappeared. At last my fridge seemed to be finally happy on 12 volt.

Next outing was only a short run, and again the fridge did not seem to be cool upon arrival on site, despite pre-cooling it etc. I wondered if the voltage on the car was dropping when all the lights and wipers were on, causing the voltage sensing relay to drop out, so I re-wired the car, and fitted a relay that triggered only when the engine was running.

When we went off to Wales last week, and as usual, pre-cooled the fridge on the Wednesday, and loaded it up on the Thursday, with many items that were frozen so they would not only help keep the fridge cool, but defrost ready to use over the next couple of days. We departed early Friday morning, and on the journey, when ever we stopped for a comfort break, I would leave the car running, run round and open up the caravan, and make sure the fridge blue light was on and not flashing, before returning to the car and stopping the engine. All seemed OK.

When we arrived on site the fridge was colder than the outside air temp, but not properly cold, but as it was a very hot day, we just thought we were being paranoid. On the home journey, the same thing happened.

Today, I decided to look into it further, and made a lead up to connect the fridge directly to a charged battery. I checked the current, and it was drawing just under 12amp, so was fairly happy the element is working, but after leaving it for an hour, when I opened the fridge, which was empty, it was like opening an oven door, the air inside was actually hot.

The fridge is in an Adria Adora and very well fitted and sealed.The 2 vents only give you access to the area directly above the flues, and the very bottom where the gas jet, and electrical connection box are. I can see the wires for the two heating elements disappear up to the area between the vents, where there is no way to get to the back, other than removing the whole unit from the van, which I do not want to do until I have some idea what I am looking for.

Anyone had this, or know where and what to look for?

[solarman216]

Not dealt with the Thetford but the hot area is the same across the board on absorption fridges, a short length of pipe that is heated by gas pilot light, 240v element and 12v element, as you are drawing the current the element should be getting hot but looking at some of the caravan forums it seem the heater can slip and so not be in good contact with the refrigerant pipe, you will need to pull it out and have a look Clive, Rick

[Lazy-Ferret]

Originally Posted by solarman216

Not dealt with the Thetford but the hot area is the same across the board on absorption fridges, a short length of pipe that is heated by gas pilot light, 240v element and 12v element, as you are drawing the current the element should be getting hot but looking at some of the caravan forums it seem the heater can slip and so not be in good contact with the refrigerant pipe, you will need to pull it out and have a look Clive, Rick

Cheers Rick, that was what I was afraid of... Any idea how I will know if it is in the right place, and how critical is the placement?

I guess I just make sure it is in the same place as the 240v element.

[solarman216]

it will have some kind of clip holding it onto the pipe, which may have rusted away, but it has to be in solid contact and have insulation around it, Rick

[Lazy-Ferret]

Originally Posted by solarman216

it will have some kind of clip holding it onto the pipe, which may have rusted away, but it has to be in solid contact and have insulation around it, Rick

Cheers... looks like that's tomorrows job.

[Mobieus_uk]

ignore my reply my idea you had already tried, note to self read posts and there is no delete button

[Lazy-Ferret]

Originally Posted by Mobieus_uk

ignore my reply my idea you had already tried, note to self read posts and there is no delete button

Oh no, and I missed the reply as well...

[solarman216]

What did you find Clive, or did you not get that far, Rick

[Lazy-Ferret]

Originally Posted by solarman216

What did you find Clive, or did you not get that far, Rick

Sorry, I was running a bit late....

It took me pretty much the whole day to actually get the fridge out... When those Slovakians fit a fridge into a caravan, they really do seal it in. In all my years of caravaning, this is the first fridge that is actually sealed properly so none of the air from the back of the fridge can get back into the caravan. There is even a slot routed in the cabinet sides, with a plastic wafer seal let in, to really make sure nothing can get past. The problem was, it was a bit too well sealed, with mastic between the fridge and the cowlings. That mastic they use in caravans is hard enough to break, but being a warm day, no sooner had I unstuck one bit, if it touched back together again, it would re-grab.

Anyway, I eventually got it out, and set to work looking into the problem. After removing the metal cowling, and all the insulating material, there is a vertical refrigeration tube that has the chimney for the flame welded to one side of it, and two smaller vertical tubes welded to the other side. In one of these tubes fits the Mains element, and in the other, the 12v one, both rated at 140w. The elements are "L" shaped, and slide down the tubes till a little bump on the element stops them going any further.







These were taken as I was putting it back together.

I took them both out, and checked them over, both were pretty clean, the 12v one being the cleanest, so I connected them up to make sure they both got hot.. Yep..

I generally cleaned up all around the area, cleaning the inside of the tubes the elements slide into, and while there, all the gas jets, and apart from a lot of burnt dust, it was all pretty good. I then re-assembled the elements, using the White Heat Sink compound as a lubricant to help slide the elements back into place.

I left it running on 12v last night, and it started at 42degrees in the fridge, but by this morning it was down to 1.2degrees in the fridge, and minus 18.6 in the freezer, so it is obviously now working...

The problem is, I do not know what I did to fix it???? The only thing I did notice was the 12V element, which is the taller one of the two was up about a 1/4 of an inch, but I can not be sure I did not catch it removing the cowling, and even if it was, with the arrangement of how they are connected to the refrigeration pipe, I can't see that making that much of a difference.

[zippy656]

Nice fridge...

Ok the two bits into flue are the elements

One is 12v other the 230

To the left is the power board,

So before you rip it out few things to check,

Easyer if you ring me then me type it all up,

07974651484

[zippy656]

Also check out the engineer only web site

thetfordservicenet.com

[solarman216]

if it is now working Clive I can only imagine that the additional heat conducting compound you used has improved heat transfer, if the 12 v element was out of it's socket by a little this could have been detrimental as well, Rick

[zippy656]

No paste needed ,

Sounds like the common plug fault.

[Lazy-Ferret]

Thanks Guys, (I was out in the car Zippy)

The guy over the road, is Gas Safe, so he just checks it over for me, once it is all back in.

No problem with the sealing it all back in, apart from the 2 joins that were mastic, the rest are reusable plastic wafers. I have some new Stickafix to re-do the two mastic ones.

I don't think it can be a plug issue, as I used exactly the same setup for both tests, besides, I can't see how a plug issue would cause it to actually get hot inside the fridge.

I think there is some witchcraft going on...

[zippy656]

No worries, check out the .com