Dometic Fridge - Help!!

[JFD]

We have a Dometic fridge (RM7655L), which is driving me (us) crazy!!

It works fine on mains - freezer gets down to minus 15, no problem: On Battery, it seems to maintain a decent temperature, although we have not done any very long runs lately - been exploring nearer to home! On gas, the gas lights fine, and seems to be working (there is a decent blue flame, and the tip of the thermocouple gets nice and cherry red) but, after a few hours, the igniter starts ticking, as if the flame had gone out (but it hasn’t), the gas indicator lamp flashes orange, and the fridge shows no sign of being cooled, gradually rising to ambient temperature, which is not good!!

The flue has been blown through with a compressor and, the top end gets just as hot on mains and gas (not measured, just too hot to touch on either!). All the usual culprit comnnectors have been cleaned, but to no avail.

Apart from scrapping it and buying a new one (can’t afford that at this time), does anyone have any suggestions as to where to look next?

 

[Jaws]

This might sound an odd unrelated question, but have you got refillable gas ?

 

[JFD]

That’s an unexpected question, but interesting! Yes, we do have a refillable gaslow system fitted. Whenever I park up, I check the gas flow with the hob, before turning the fridge to gas. Am I missing something?

 

[Jaws]

That’s an unexpected question, but interesting! Yes, we do have a refillable gaslow system fitted. Whenever I park up, I check the gas flow with the hob, before turning the fridge to gas. Am I missing something?

OK.. the chances are, no matter how good it looks, there will be a bit of a blockage in either the burner or the little restrictor that is often fitted immediately before the burner ( often made as part of the burner )
The only way to deal with it is take the burner off and give it a thorough clean, as well as using a nozzle 'pick' to completely clean the restrictor jet.

I have seen the problem a few times over the years.
Pump LPG has a lubricant in it ( tiny amount ) which I understand is used to minimise valve stem wear on engines..

It turns in to astuff that looks and feels like resin.. And when it gets hot it slowly goes runny

The only cure is a bloody good clean !

I would also be inclined to run a brush or similar up the flue ..A compressor will not shift the caked on stuff.
I had an awkward bugger to get at a while ago. I wangled a long bit of wire down from the top, pulling it through by about 4 feet
I attached a small bit of cloth half way along it and pulled it up and then back down a few times.. the amount of crud that fell out surprised even me !

 

[glenn2926]

Just a thought, the van is level is it? I had this problem when i first bought my van. I levelled it up to within the recommended three degrees and have not had any problems since.

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[JFD]

Thanks for that. I have cleaned the burner pretty well, and the flame looks to be a healthy size, but I wasn’t looking for baked on resin! I will reclean the jet again, and have a go at cleaning the flue as you describe!

 

[JFD]

Yes, the van is straight and level, to within a degree, according to the two-way bubble level we use.

 

[Fletton]

What temp setting is the fridge set to....

Some find their fridges cool better set mid-way rather than set to max...

Mine certainly does ....

 

[JFD]

We have ours set to around 3/4 full. I have heard that full on can cause problems in the past, so we tend to run it with 3 lights of 4 illuminated.

 

[Bart]

@JFD we had a similar clicking problem on our Thetford fridge despite their being a good well lit flame.
Different fridge but might be relevant here is my thread on it.
https://www.motorhomefun.co.uk/forum/threads/thetford-fridge-not-working-on-gas.164873/

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[Lenny HB]

Following on from @Jaws answer, have you filled up with LPG in France. I heard several stories of people having to clean the jet & burner after because French autogas sometimes has more of the oily residue in it. When we bought our first van I remember our Belgium dealer said to us don't fill up in France the gas is dirty.

 

[dpsuk999]

If the fridge works ok on gas but fairly frequently the igniter begins to click as if trying to light again then you may find the multi connector going to the burner control device is loose and the little connectors are not making a good connection. The first pic is the connector, the second pic if you look close you can see the gap and then the third pic with the gap closed. Mine has been perfect since.

 

[JFD]

Thanks all, for your feedback and advice.

Our gas flame stays alight, but there seems to be zero cooling effect inside the fridge or freezer. After a while, the igniter starts clicking as if the flame had failed, but it has not. The burner seems clean - no apparent residue from lubricants in the LPG. I have also tested all the connections, including earths, and they all register as OK on the Avometer. Next is the flue - need to get the top off, so I can drop a line down to drag a cleaning rag through!

 

[JFD]

Well, the top is impossible to remove without either taking the fridge out, or drilling a sizable hole in the side of the vehicle. I managed to stick my finger into the upper side of the diffuser, and it wasn’t caked with anything, just a little dusty/dirty - no soot or evidence of major clogging, so I will concentrate on other avenues!!!

 

[tonyidle]

Buy a new burner unit. It's a simple swap, not too dear, and solves corrosion and blocked jet problems. Quite simply, if it's OK on electric, the gas side isn't getting hot enough and a burner change, especially if the fridge has seen a bit of life, is a total cure.

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[Jaws]

Well, the top is impossible to remove without either taking the fridge out, or drilling a sizable hole in the side of the vehicle. I managed to stick my finger into the upper side of the diffuser, and it wasn’t caked with anything, just a little dusty/dirty - no soot or evidence of major clogging, so I will concentrate on other avenues!!!

This is all very very odd..
The only thing left is the main board .. or else the gas flame is simply not getting the heat exchanger warm
But that would not explain why the igniter kicks in..I think it is time to give Dometic a ring.. Unlike Thetford, they are pretty bloody helpful

 

[Lenny HB]

Agree with @Jaws sounds like the board in the black module on the back that controls the ignition, that's if they are similar to the 8000 series, they are the wrong side of 200 quid.

 

[namwaldog]

On the images that @dpsuk999 shows, the light grey "box" that the connectors go onto is the Burner Control Device. We have a similar one on our 8XXX series which we had to replace. The two wires that go into the BCD with red and black plugs both come from the burner. One to the igniter and the other to the thermocouple but cant remember which but due to the physical size of the red & black plugs, they are not interchangeable and cannot be put in the wrong hole.

You say the thermocouple is glowing but the fridge is still trying to ignite so there may be a problem with the thermocouple connecting to the BCD. Worth testing that part of the wiring?

I think the 7XXX have a similar wiring setup.

Barry

 

[JFD]

Ok, progress report: I dismantled the burner, so I could clean the jet thoroughly. After advice on here, I submerged it in boiling water and, lo and behold, several patches of oily residue floated to the surface!! Thanks for that pointer Jaws!

All now reassembled and, after the traditional clout of the gas valve with a wrench, a bigger, bright blue flame sprang up! Time will tell if there’s enough heat to chill the fridge, but here’s hoping!!

Thanks to all who contributed suggestions. Further progress report later (if it stops raining!!)

 

[JFD]

Checked the fridge this morning: Still got a nice big blue flame, and the fridge and freezer are still at ambient temperature!!!

Given that it works fine on 240v, anyone have any idea where I should attack next?

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[Jaws]

Well I am completely baffled !

 

[sallylillian]

Is the burner holder correctly mounted? The flame must play directly onto the pipe. After some work on ours the engineer left a screw off and travelling caused the whole assembly to move away from the pipe. This also caused some blow back onto the condensate collector causing some burn damage. If the flame is strong and the condenser works with 230vac it must be that the flame is not enveloping the pipe. Worth a good check, especially as you have had it apart multiple times.

 

[JFD]

That’s a good point, sallylillian. When dismantling the jet, I noticed that the jet was not firmly attached to the pipe at the end of the flue. The bolt attaching it is not original - too shiny! On reassembly, I did notice that I couldn’t do the bolt up sufficiently to anchor the jet, but assumed that it was probably close enough (1-2mm) to where it should be. I will find a replacement bolt with the right thread, and see if that makes any difference.

 

[JFD]

No difference. Back to the circuit diagram!!! Does anyone know of a motorhome refrigeration expert anywhere in Surrey/Kent???? Or a mobile one in this neck of the woods????

 

[JFD]

Back to basics: Put MoHo on electric hook up, to make sure the refrigerator bit still works!

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[Richard and Marie]

I have this week fitted a new RMD 8501 to our 5 year old Rapido PVC. When connecting the gas line to the new fridge I noticed what appeared to be a bit of foam debris in the elbow connected to the gas valve. Tried sucking it out with a vacuum cleaner with no luck so I checked the old fridge and it too had had the foam in the elbow.
I have since removed the elbow from the old fridge gas valve and blown the foam out with an airline and it appears to be a filter.
I have no idea if the 7 series or other models have this filter but I thought I should share this info.
Hopefully there should be some pics attached.

 

[JFD]

Thanks, . I will have a look at my filter and see if that is affecting the gas flow, although the flame looks strong, and the sensors in the flame are glowing a nice cherry red! At this stage, I will try anything!

The fridge is back on mains at the moment, just to ensure that none of my work so far has disturbed it’s ability to chill!!!

 

[JFD]

Working on mains, the freezer gets down to -15 no problem, so the refrigerator still works.

The gas filter seems fine - looks just like the roll-up filters we used to use years ago!!! The puzzle is why the mains works fine, but the gas does nothing. Not sure about the 12v, but both mains and gas work, if I understand it correctly, by chucking heat up the flue, within which is the heat exchanger to separate the refrigerant from it’s solution. If one works, why would the other not work?

Next on the agenda is a good (via mirror) look up the flue, to see of there is any obstruction to the heat from the flame, although the top of the flue gets very hot on either gas or ‘leccy operation!!

 

[tonyidle]

If the flame is adequate you should hear a gentle 'roar' at the lower vent.

If the fridge works on mains the cooling unit is working correctly. On gas, once the flame is established, electronic play no part unless the flame fails to heat the flame failure device. So the problem revolves around the burner, the chimney, or (much less likely) the gas valve. Any corrosion that narrows the slots on top of the burner will have a dramatic effect on the amount of heat it can produce. My previous advice still stands - change the burner.

 

[JFD]

Looked at replacement burners - seems to be around £100 for the one to fit my fridge, which is a lot, when I don’t know that it needs replacement!

Decided to check the flue as far as possible, with the fridge in situ, so removed the burner, and used a thickish cable to see if there were any obstructions - there were none, and no shower of anything coming down. Really can’t see why it shouldn’t work.

Re-assembled everything, and fired it up, and it works!!! Just made some ice in the icebox, which is down to -10 degrees. Just checking the fridge, but it seems to be working, too.

Who knows why???

Thanks for all your helpful suggestions!

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