Thetford Fridge 3-Way on Gas

[snapster]

Seems a little slow on gas, mine seems to cool down about the same on gas as AC and, when my gas jet was blocked, cooled down from 12 degrees to 4 on 12v in a couple of hours, with a full fridge when we were travelling. I know my fridge is Dometic, but they must work in a similar way.
There could be debris inside the burner itself, restricting the gas flow, so it might be worth cleaning out inside too, an easy job if you are going to clean the jet.

 

[wildebus]

I reckon that one of the reasons it may be slow is there is a plate missing from the burner and that is allowing heat to escape.
This is a still from a Youtube video that someone posted of the same type of Thetford fridge and burner assy.

That plate that is hanging down in the image above that the guy is in the process of removing ... I don't have one of those at all.
Should be easy enough to fabricate a replacement (maybe someone at the Kelso Meet will have the same fridge and I can check out their plate for the shape and bends )

 

[wildebus]

I reckon that one of the reasons it may be slow is there is a plate missing from the burner and that is allowing heat to escape.
....
Should be easy enough to fabricate a replacement (maybe someone at the Kelso Meet will have the same fridge and I can check out their plate for the shape and bends )

Running some wiring around the van and opened up the cupboard under fridge to see how I could route a cable and I only happened to find the burner plate lying in it at the back!
Normally I would have only found that after paying £30 to buy the official bit of bent tin from Thetford
Bit of a result! See if I can fit it in the morning if it is not raining still

 

[Mads]

I reckon that one of the reasons it may be slow is there is a plate missing from the burner and that is allowing heat to escape.
This is a still from a Youtube video that someone posted of the same type of Thetford fridge and burner assy.
View attachment 60146
That plate that is hanging down in the image above that the guy is in the process of removing ... I don't have one of those at all.
Should be easy enough to fabricate a replacement (maybe someone at the Kelso Meet will have the same fridge and I can check out their plate for the shape and bends )

Thanks for this, my fridge hasn’t been igniting on gas for about a month. I tried to get to it and couldn’t get access to it. I took it to somebody, who told me little more than I already knew. They didn’t get back to with an estimate or when they would fix it. This inspired me to look at YouTube this morning. I worked out that the surround has to come off before the housing around the burner. I took the burner out and gave it a clean along with ignition electrode and the thermocouple. I Replaced the tape that was around the ignition wire and put it all back together.

It now works!

 

[mr brown]

pretty sure the tin shield round the burner is to windproof the flame and stop anything touching the flame, i doubt it has anything to do with the efficiency . needs to have one though for the above reasons

 

[Markd]

Glad to hear you've got it starting and found the shield.
It's certainly worth taking the burner out and cleaning it up to improve flame - you can do that without disconnecting the jet itself.
I suppose you could try cleaning the jet with a fine wire - in-situ is diy but don't try to make hole any bigger.

The other thing that might improve overall cooling performance would be to clean the flue - probably just tapping it and vacuuming the crud that falls down will do the trick.

If the weather was very hot you might be concerned about airflow over the external cooling fins and some people swear by 12v 'computer' fans.

On three way adsorption fridges gas is normally reckoned to be the most effective power source so it does sound as if there's some improvement to be had.

 

[wildebus]

I've been looking at a few youtube videos and I see that Thetford and Dometic burners are very different.
On a Dometic there seems to be no physical connection between the gas jet outlet and the burner - the gas appears to just carry on through an open gap (seems very weird), so the burner part can be removed/cleaned without disturbing the nozzle
On a Thetford the jet/nozzle is within the burner assy at the end so would need to be removed to clean the burner. I'll be attempting that (assuming nothing has seized up that prevents doing it).

I had a look inside the top vent cover and can't even make out a flue exhaust so will need to clean the flue best as possible from below only (after removing/covering the burner to stop anything dropping into it).

 

[wildebus]

Burner out and gave the flue a good old tapping with the end of a screwdriver ....

Not a massive amount of soot really I think (maybe it is though?) but certainly wouldn't really want that dropping into the burner assembly.

The Fridge is starting instantly on gas, which was the original issue I was wanting to resolve, so that is sorted which is great. A little photo of the burner as it is running now (before I put the covers back though of course)

It looks pretty good to me?

There is an little caveat to this now ... There are 5 slots in the burner and in the photos and videos of the burners on line they are all open.
However I had some inserts in the burner which must act as some kind of restrictor?
The first photo shows the burner as I took it out. The second photo shows the plates removed (they are loose and just drop into the slots)

I took them out to give the burner a bit of a blow-out with a compressor (nothing came out) and decided at this stage to leave them out (kept though in case need to go back) and reassembled the complete burner area assembly



Have to see how it goes now. The Fridge is 17C right now. Let's see what happens!

 

[Markd]

I suppose that the separate jet and burner system means that operator cleaning is 'legal' as it doesn't require disassembly of the gas system?
Personally I reckon that if we can be trusted to change a gas bottle we should be capable of undoing and retightening the union on the jet.

Whether you get a restriction with the extra bits is debatable as the amount of gas going through the burner is controlled by the size of the jet and the pressure regulator.
That flow of gas draws in air and you get a nice blue flame if enough air can get in - which is why we have to clean burners a d inlets regularly.
On a complete aside I have a gas tumble dryer that draws air in at floor level and after 20 years fluff built up in the burner venturi giving me a very cold orange flame that extended way too far into the duct and sooted it up. None of the service instructions ever talked a out this potential problem and I had to completely dismantle the burner assembly to get at it. I guess similar things could happen with Truma boilers if used a lot.

Removing the 'diffusers' may make the flame less stable?

Hopefully you have improved the flow up the flue and will see better performance.
If you decide to clean the flue more proactively you may find some bits hung in it to aid heat transfer.

 

[wildebus]

The inserts/restrictors/diffusers/whatever would heat up and maybe change the heat of the flame?
I still have them and they literally drop into place withut any dismantling more than taking off the top cover for burner access so can try a before and after.
Fridge on and cooling, albeit very slowly (I think, but I have never had a 3-way fridge before)

 

[Markd]

I read that gas fridges get colder in hot weather if they have thermostat set mid range.
I know that's counter intuitive but a few people agreed - or an myth perhaps but no harm in easing it off.
FWIW my Dometic fridge-freezer gets very cold on gas and will comfortably get sub zero in the fridge at low settings.
I can feel a good flow of heat coming out the upper vent above the flue.

 

[Markd]

The inserts/restrictors/diffusers/whatever would heat up and maybe change the heat of the flame?
I still have them and they literally drop into place withut any dismantling more than taking off the top cover for burner access so can try a before and after.
Fridge on and cooling, albeit very slowly (I think, but I have never had a 3-way fridge before)

I noticed that with diffusers in your flame was nicely shaped drawing into the flue.

 

[wildebus]

I noticed that with diffusers in your flame was nicely shaped drawing into the flue.

that photo is with the little inserts removed in fact.
currently the fridge has only lost 4 Cel. Will be interesting what it is in the morning.

 

[Markd]

Ah! - good flame anyway.
I think it should be cooling much faster than it is.

 

[wildebus]

Right .... So the fridge is cooling, but slowly and not getting that low in temp. I switched from gas to 240V and it didn't cool any further (the setting it was on is one off the max).
It had a bit of a glitch a little while back and it cooled down to about -10C in the fridge area and then seemed to go into maintenance mode. Cleared that by a bit of power cycling and waiting...

So situation now is the following:
The SES (Smart Energy Selection) works perfectly and detects 12V and 240V and switches as appropriate.
When the fridge switches to gas from 240V or 12V, the burner ignites within a click or two. Switch from gas to 240V, gas stops, switch back, gas lights straight back (taking 12V - Gas delay into account of course).
Cleaned Burner; 'cleaned' flue by tapping to dislodge loose soot.
The performance on Gas and 240V seem to be pretty comparable.

Now I was checking the temp and it went down to around 8C and nothing in freezer was frozen (there was some ice on the rear side of the compartment so som cooling was happening). But the side of the van where the vents are was in direct sun and the temp of the side of the van was over 40C - could this be impacting the performance? (The temp was for sure from the sun, not the fridge).
(I just checked the freezer this morning and generally cold but not frozen - temps at back were -10C on the surface so something is happening but just not enough?)

Any suggestions to make it perform better? I have seen suggestions like remove and invert to redistribute the coolant - that would be an extremely awkward procedure for a large built-in fridge. How many people ever do this? How much performance would/could you expect from a 13 year old 3-way fridge? Good as when it was new? What level of servicing is worth it compared to buying a replacement?

 

[Markd]

Given the ambient temperature I think you should consider setting the required temperature to mid range - surprisingly this is suggested in User Instructions.
To work properly heat has to go in one side - (which you have sorted) and dispersed on the other from the cooling fins.
The manufacturers do sell very expensive fans to fix under the fins to improve dispersal.
I found this neat looking kit with control panel for a more reasonable price

Motorhome Double Fridge Fan - Outdoorbits

The turning speed of both fans is electronically controlled through temperature sensor. Complete with control ... Read more

www.outdoorbits.com

Similar models available at different prices

Or you could go DIY for a much lower price - my van has a manually switched single fan that just draws air generally up the void which might do something - I haven't used it because I haven't experienced cooling problems.

I would expect performance to be maintained throughout working life - unless chemicals leaked out when I'd expect complete failure.
Fins may benefit from periodic dust removal which ought to be easy enough.

They are very expensive to replace and nowadays (particularly with the battery capacity you have) it would probably make sense to go compressor fridge.

 

[wildebus]

I went in this morning and set the "bars" to 3 from 4.
Counter-intuative really but worth a go.
What I have noticed is the fins withinn the fridge are not getting iced up or even remotely frosted - and I think that should be happening when the fridge is operating.
I could give the whole backside a good blast from a compressor I guess and dislodge/clean the surfaces.
It's frustrating really as it is working in that it's cooling, so that suggests coolant is present, etc, but it is not cooling to really be a fridge - it's more like a very large coolbox.

It's pretty well 80/20 (or higher) I think in terms of taking it out and sticking in another (and another would 100% be a Compressor Fridge). The only thing stopping me doing that already is the hassle of removing it (fridge is bigger than the door!)

 

[wildebus]

Just for fun I put the two little restrictors/diffusers/blockers/whateverthehelltheyare back in the burner. They must serve some kind of purpose!

You can see them in the photo below in the last two slots and the flame is all around them and looks no different (and nice and healthy?)

I'd be interested to know what their purpose is. They are not just bits of metal dropped in, they are sized and shaped.

Still on the gas (and setting on 3rd bar on control) - let's see what the temp does

 

[Markd]

You should be getting a good coating of ice on the internal fins - so it's definitely not cooling properly.
There are some 12v compressor fridges sized to match absorption - from marine market I think.
You may find that with doors off the old fridge might go through the door sideways?
But you're still stuck getting the new one in
Was it earlier in this thread that someone suggested using passenger door with seat removed?
A lot of people swear by fans to increase airflow over external fins and that's a reasonably cheap option if it works and not the end of the world if it doesn't. You've still got them available if needed behind a compressor fridge.

 

[wildebus]

You should be getting a good coating of ice on the internal fins - so it's definitely not cooling properly.
There are some 12v compressor fridges sized to match absorption - from marine market I think.
You may find that with doors off the old fridge might go through the door sideways?
But you're still stuck getting the new one in
Was it earlier in this thread that someone suggested using passenger door with seat removed?
A lot of people swear by fans to increase airflow over external fins and that's a reasonably cheap option if it works and not the end of the world if it doesn't. You've still got them available if needed behind a compressor fridge.

The fridge is 1cm wider than the door. I measured the width from the rear inside the vent and I might - just might - be ok if I take the door and front trim surround off (width-wise is a no-go - the fridge is deeper than it is wider).
On my quest for info I watched a little Aussie Youtube video of a guy swpping an ancient 3-Way for a 2nd hand compressor fridge and he had fun taking out the old and bringing in the new he did it and what he found was precisely what I would find (hope!) would happen - got it out the door but with zero room to spare and taking the door lock off - but still got it swapped
He said he also booked a guy to remove a window but in the end got away without it!
If it doen't go through the hab door it should go through the cab door with seats removed.

I can certainly get a like-for-like 12V Compressor to match the hole left exactly and that would be the ideal. I have also got a couple of other options ... There is a Webasto Cruise 165 12V Compressor Fridge which is an excellent fridge I believe and would fit in the gap and would need a bit of packing - but it will go through the door! That is important to my mind for servicability.
I am also toying with the idea of two fridges! I could potentially get a pair of Waeco CRX65 Units in the gap stacked together. These are good fridges and you can use each one as a Fridge, as a Fridge/Freezer, or as a straight Freezer. The flexibility that gives you is tremendous and you can change the setup depending on what you want for a trip, including only using one of them if it is maybe just a few days away and you don't need so much space, or if in the winter when you want to reduce electrical power useage


Ref the fans - I added a 12V Fan to the back of my 240V Fridge in the camper with a programmable thermocontroller so it would come on and off automatically. That actually worked very well and when it came on would usually cool the rear by around 4C within a few minutes with the extra airflow so I see a value in the principle. In this case, if that extra cooling would be the factor I would expect the overnight fridge temp to go decently lower as the sun is in (it drops by maybe 1C only?). It may be summertime, but this is still Scotland!


If (when really!) I do swap the fridge out, once the old one is out will be able to properly look at it and hopefully get it working properly (maybe it just needs to be inverted for a while with the coolant?) and then sell it on as a fully working unit to help cover some of the compressor fridge cost