3 way fridge problem

[nicknorman]

Ok so this is on my caravan, but could be same on a boat. Thetford 3 way fridge which I always run on gas. It has auto-ignition and a thermostat so the flame can cut in and out, which it used to do.
 

Over the last few months it’s been getting less effective, and now (even before the recent very warm weather) it is barely cooling. The flame is on permanently, the back of the fridge, fins, pipework etc are warm or hot. But the inside of the fridge remains only just below ambient.

 

So presumably some failure of the refrigerant to circulate? Does anyone have any ideas how to fix it please?

[Tracy D'arth]

Clean out the flue tube and the burner assembly, they get coked and fluffed up. They all do this. If it has lost its refrigerant it does not work at all.

[Tony Brooks]

A couple of ideas.

 

1. Ensure the flame is blue and not yellow, if it is yellow take the fridge out and dismantle the burner to blow the spiders out, I would also remove the jet/injector and ensure it is clear.

 

Make sure the flue is clean and the "whirlygig" is in place.

 

2. if that does not work then take the fridge out, invert it and attack the pipework at the back with the heel of a slipper. return to the right way up and attack it again.  NOTE, never do this on a compressor fridge.

3 minutes ago, Tracy D'arth said:

Clean out the flue tube and the burner assembly, they get coked and fluffed up. They all do this. If it has lost its refrigerant it does not work at all.

 and you would be complaining of an ammonia smell.

[nicknorman]

Thanks both, I will try all that. I had heard about the “turn it upside down” thing but wasn’t sure if it had any scientific validity, thanks for confirming it does!

 

I did replace the burner tube a few years ago when the flame failure device was failing, but the caravan is in the Highlands with all sorts of beasties about so I will check the burner again.

 

[Tony Brooks]

7 minutes ago, nicknorman said:

Thanks both, I will try all that. I had heard about the “turn it upside down” thing but wasn’t sure if it had any scientific validity, thanks for confirming it does!

 

I did replace the burner tube a few years ago when the flame failure device was failing, but the caravan is in the Highlands with all sorts of beasties about so I will check the burner again.

 

 

I can't give you any scientific reason, but it does seem to work. I suspect it either gas locks or some of the chemicals precipitate out. We did it all the time on the hire fleet.

[bizzard]

2 hours ago, nicknorman said:

Thanks both, I will try all that. I had heard about the “turn it upside down” thing but wasn’t sure if it had any scientific validity, thanks for confirming it does!

 

I did replace the burner tube a few years ago when the flame failure device was failing, but the caravan is in the Highlands with all sorts of beasties about so I will check the burner again.

 

By removing the burner tube should reveal the gas jet which sometimes gets goooo'd up. Gently probe it with thin wire or with 5 or10 amp fuse wire.

[nicknorman]

18 minutes ago, bizzard said:

By removing the burner tube should reveal the gas jet which sometimes gets goooo'd up. Gently probe it with thin wire or with 5 or10 amp fuse wire.

I think the actual flame is fine. It has electronic flame failure detection and after the burner tube got corroded, the flame shape was wrong and not touching the electrode, so it would not stay lit. But a new burner tube fixed that problem. There is plenty of heat but no cooling!

[Tracy D'arth]

30 minutes ago, nicknorman said:

I think the actual flame is fine. It has electronic flame failure detection and after the burner tube got corroded, the flame shape was wrong and not touching the electrode, so it would not stay lit. But a new burner tube fixed that problem. There is plenty of heat but no cooling!

OK, don't belief, go and buy a new fridge. Is that the answer you were looking for.  Happy now?

[alan_fincher]

4 hours ago, Tony Brooks said:

I would also remove the jet/injector and ensure it is clear.

 

Don't be tempted to push any wire, or similar, into the jet.  They have a very fine mesh in them, and this will destroy it.

[Tony Brooks]

53 minutes ago, nicknorman said:

I think the actual flame is fine. It has electronic flame failure detection and after the burner tube got corroded, the flame shape was wrong and not touching the electrode, so it would not stay lit. But a new burner tube fixed that problem. There is plenty of heat but no cooling!

 

Sorry Nick, but so far you have provided no proof for that assertion. By all means tell Tracy, Biz and myself that we are wrong, but at last follow the suggested diagnostic procedure, so you can prove it. If you don't want to follow the diagnostic advice, why ask the question, just do your own thing.

[MtB]

1 hour ago, bizzard said:

Gently probe it with thin wire or with 5 or10 amp fuse wire.

 

One needs to be dead careful doing this. I consider myself careful and still managed to convert a small pilot light into a blowlamp once. The gas jet turned out to be a hole in a piece of ally about 10 thou thick! 

 

Ever since then I've found boiling the gas jet in white vinegar for several minutes restores it to near-new condition, and clears out all the crud. Even the invisible crud. Makes for excellent 'theatre' in the customer's kitchen too. Stinks the house out!! 

 

 

 

[BEngo]

If you can remove the jet blow it through backwards with an air duster. 

 

Does it work on 240V or 12 V ?

  If not then the "invert it and shake"  treatment is indicated. That works by re-dissolving the ammonia gas IIRC.   If that doesn't cure it the ammonia has escaped, probably while you were away boating so you would not notice the smell.

 

N

[nicknorman]

1 hour ago, BEngo said:

If you can remove the jet blow it through backwards with an air duster. 

 

Does it work on 240V or 12 V ?

  If not then the "invert it and shake"  treatment is indicated. That works by re-dissolving the ammonia gas IIRC.   If that doesn't cure it the ammonia has escaped, probably while you were away boating so you would not notice the smell.

 

N

I don’t have 240v and the 12v only seems to work when the car is plugged in - caravan has not moved or been plugged into a car for a decade! But it is all getting very hot at the back so I’m confident the heat source isn’t the problem.

 

Ive been busy installing an oxygen system in someone’s glider today, and it’s too hot for working in a caravan anyway. I’ll have a go at taking the fridge out and giving it the upside down shakes this evening when it’s cooler.

[Tracy D'arth]

Why  can you not accept that the first thing to check is the burner/exhaust before you take it out and turn it upside down? The collective opinion here from folk who have been fixing these for years is that it is likely to be the flame picture is not correct.

 

If you cannot accept advice when you ask for it, stop asking. Its very bad manners.

 

[MtB]

10 minutes ago, nicknorman said:

But it is all getting very hot at the back so I’m confident the heat source isn’t the problem.

 

 

Hotter than it used to get?

 

If so, then the heat energy that used to get absorbed doing the cooling is perhaps no longer being absorbed. Or worse, is spilling out instead of passing up the flueway.

 

Bear in mind I know nothing about absorption fridges. Compressor fridges are challenging enough to remember how they work. I had a look on youtube to see how absorption fridges work and it just gave me a headache. 

 

 

 

[nicknorman]

1 hour ago, Tracy D'arth said:

Why  can you not accept that the first thing to check is the burner/exhaust before you take it out and turn it upside down? The collective opinion here from folk who have been fixing these for years is that it is likely to be the flame picture is not correct.

 

If you cannot accept advice when you ask for it, stop asking. Its very bad manners.

 

 

10 hours ago, nicknorman said:

Thanks both, I will try all that. I had heard about the “turn it upside down” thing but wasn’t sure if it had any scientific validity, thanks for confirming it does!

 

I did replace the burner tube a few years ago when the flame failure device was failing, but the caravan is in the Highlands with all sorts of beasties about so I will check the burner again.

 

I thought “thanks both,” (one of whom was you) “ I will try all that.” covered it. I know things are not easy for you at the moment but please don’t look for fights where no grounds exist. It won’t help.

 

Tonight I took the fridge out, which is the easiest way to access the burner and flue tubes.  I cleared out the flue tube which had some carbon in it, checked the burner tube which looked clean, turned the fridge upside down, belted it. There was a lot of gurgling which I am hoping means there is still ammonia in it.

 

I’ve  now put it back in and lit it, hopefully it might start cooling now.

56 minutes ago, MtB said:

 

Hotter than it used to get?

 

If so, then the heat energy that used to get absorbed doing the cooling is perhaps no longer being absorbed. Or worse, is spilling out instead of passing up the flueway.

 

Bear in mind I know nothing about absorption fridges. Compressor fridges are challenging enough to remember how they work. I had a look on youtube to see how absorption fridges work and it just gave me a headache. 

 

 

I think it is hotter than it used to be, but I think that is simply because the burner is on continuously as opposed to going on and off from time to time under the control of the thermostat. The “hot” things are the pipes and fins at the back of the fridge, not just the burner.

 

FYI the installation in a caravan is quite different from a boat. In a caravan there is a cavity behind the fridge, sealed to the inside but ventilated to the outside by two large grills, one near the bottom and one near the top

Edited September 5, 2023 by nicknorman

[MtB]

1 minute ago, nicknorman said:

 

I thought “thanks both,” (one of whom was you) “ I will try all that.” covered it. I know things are not easy for you at the moment but please don’t look for fights where no grounds exist. It won’t help.

 

Tonight I took the fridge out, I cleared out the flue tube which had some carbon in it, checked the burner tube which looked clean, turned the fridge upside down, belted it. There was a lot of gurgling which I am hoping means there is still ammonia in it.

 

I’ve  now put it back in and lit it, hopefully it might start cooling now.

 

With boilers and compressor fridges a lot of information about what might be wrong can be gleaned from feeling the temperatures of various the pipes in sections of in the circuit(s). One can probably do similar with absorption fridges. 

 

If it hasn't responded, can you jury-rig a gas pipe and run the fridge on the worktop with its back to you, so you have proper access while its on? 

 

 

[nicknorman]

3 minutes ago, MtB said:

 

With boilers and compressor fridges a lot of information about what might be wrong can be gleaned from feeling the temperatures of various the pipes in sections of in the circuit(s). One can probably do similar with absorption fridges. 

 

If it hasn't responded, can you jury-rig a gas pipe and run the fridge on the worktop with its back to you, so you have proper access while its on? 

 

 

See previous reply. In a caravan, there is good access from outside via the large and removable grills. All the pipes etc can easily be felt with the fridge in situ. However I am not really sure which bits should be hot and which cold!

Edited September 5, 2023 by nicknorman

[MtB]

8 minutes ago, nicknorman said:

FYI the installation in a caravan is quite different from a boat. In a caravan there is a cavity behind the fridge, sealed to the inside but ventilated to the outside by two large grids, one near the bottom and one near the top

 

 

Hmm that's interesting! So effective room sealed. 

 

There is probably no reason in principle not to do similar in a boat but with a pair of ducts leading vertically up and through the roof. 

 

No reason other than it isn't what the manual says to do, that is. 

 

 

[nicknorman]

Just now, MtB said:

 

 

Hmm that's interesting! So effective room sealed. 

 

There is probably no reason in principle not to do similar in a boat but with a pair of ducts leading vertically up and through the roof. 

 

No reason other than it isn't what the manual says to do, that is. 

 

 

Yes it is room sealed. Obviously the problem with such an installation in a boat is that the annoying water would want to come in at least through the lower grill.  It relies on convection to remove the hot air so I don’t think you could have both ducts leading out through the roof. You could possibly have one sufficiently above the water line and the other going out through the roof.

[Tony Brooks]

3 minutes ago, nicknorman said:

See previous reply. In a caravan, there is good access from outside via the large and removable grills. All the pipes etc can easily be felt with the fridge in situ. However I am not really sure which bits should be hot and which cold!

 

The flue usually runs up what you may call a boiler that is surrounded by a thin metal or plastic cover with insulation between it and the boiler. The pipe that is usually a bit off horizontal at the top should be hot, and its matching pipe at the bottom should be cooler.

 

I note that you did not mention the little bit of twisted metal that usually sits down the flue to cause the hot flue gasses to swirl.  With no swirl, the heating effect will be far less.

[MtB]

1 minute ago, nicknorman said:

Yes it is room sealed. Obviously the problem with such an installation in a boat is that the annoying water would want to come in at least through the lower grill.  It relies on convection to remove the hot air so I don’t think you could have both ducts leading out through the roof. You could possibly have one sufficiently above the water line and the other going out through the roof.

 

 

Or.... 

 

Have the air supply duct discharging at or near floor level inside the 'combustion chamber', and the exit pipe connected at the top. That way when the fridge lights up, the top of the chamber will get hotter tan the bottom and the warm POCs will waft up the exit pipe connected to the top, and the cooler outside air will fall down the other tube to the base of the combustion chamber. 

 

The would need some thorough testing and some sort of safety interlock to shut off the gas if the system failed. but would probably fail a BSS anyway! 

 

 

 

[Tony Brooks]

3 minutes ago, nicknorman said:

Yes it is room sealed. Obviously the problem with such an installation in a boat is that the annoying water would want to come in at least through the lower grill.  It relies on convection to remove the hot air so I don’t think you could have both ducts leading out through the roof. You could possibly have one sufficiently above the water line and the other going out through the roof.

 

I think you can. That is exactly like the expensive Dometic gas fridge was with its balance flue. Likewise, the Alde 292x boilers. Neither had  any sort of fan and relied upon convection.

[nicknorman]

Just now, Tony Brooks said:

 

The flue usually runs up what you may call a boiler that is surrounded by a thin metal or plastic cover with insulation between it and the boiler. The pipe that is usually a bit off horizontal at the top should be hot, and its matching pipe at the bottom should be cooler.

 

I note that you did not mention the little bit of twisted metal that usually sits down the flue to cause the hot flue gasses to swirl.  With no swirl, the heating effect will be far less.

Ok I will check the temperature difference there. Yes there was a funny wire thing located at the top of the flue and dangling down. I wasn’t quite sure what it was for. It was in a slot, I therefore wondered if it was a jiggler that could be rattled around to loosen carbon in the flue. Anyway, whatever if is for, it is present and correct.

[Tony Brooks]

3 minutes ago, nicknorman said:

Ok I will check the temperature difference there. Yes there was a funny wire thing located at the top of the flue and dangling down. I wasn’t quite sure what it was for. It was in a slot, I therefore wondered if it was a jiggler that could be rattled around to loosen carbon in the flue. Anyway, whatever if is for, it is present and correct.

 

The inverted U on the top of the wire thing usually sits in a slot to locate it, but did you pull it out. The twisted metal part can carbon up. Bear in mind, I have not seen one in real life for many years.