On a recent trip I noticed the plastic cover of the boiler flue vent on my Dometic 3-way fridge has become discoloured from heat - see attached photo. Max daytime temp was about 32deg and that side of the van was sitting in the morning sun, so the gas was on practically non-stop to try and cool the thing down, and the flue vent was getting too hot to touch. Has anyone else had this happen? Is this normal under heavy usage, or indicates a problem? Thanks.
-- Edited by Mamil on Wednesday 3rd of October 2018 09:49:25 PM
-- Edited by Mamil on Wednesday 3rd of October 2018 09:49:41 PM
Hi mamil,
Is the fridge working ok ie keeping cool in the main section, freezing in the freezer? I assume you were running on gas.
In the temperatures where you are, I would suggest a shade be added to that side of the van over the fridge. See my post in Hints, Tips & Great Ideas for what I did for our previous camper. The flue definitely gets hot - there is a gas burner down at the other end. It has to boil the ammonia solution to cool the fridge down.
Just make sure some enterprising insect has not built a mud nest in the vent holes.
Mamil said
08:32 AM Oct 4, 2018
Warren-Pat_01 wrote:
Hi mamil, Is the fridge working ok ie keeping cool in the main section, freezing in the freezer? I assume you were running on gas.
In the temperatures where you are, I would suggest a shade be added to that side of the van over the fridge. See my post in Hints, Tips & Great Ideas for what I did for our previous camper. The flue definitely gets hot - there is a gas burner down at the other end. It has to boil the ammonia solution to cool the fridge down. Just make sure some enterprising insect has not built a mud nest in the vent holes.
Yes on gas, and no, the fridge was not managing to keep things frozen. So there's no doubt the gas boiler was working hard, and good suggestions on other measures to take to keep it from needing to work that hard, and in fact I've already ordered a fan to force ventilation over the cooling fins. However, point remains that I would have thought flue parts would be designed to take the temperature at max. operating output without starting to breakdown - which is essentially what turning brown is for plastic?
Possum3 said
10:10 AM Oct 4, 2018
Plastic vents normally supplied by cheapest import from Asia, fortunately they are cheap enough to replace if cannot be cleaned up.
Point to note with fridge is as Warren said keep it shaded from direct sun on that side of van.
Also instead of turning fridge up to maximum turn it down to about 3/4 this allows the fridge to cycle better and as weird as it seems stay colder.
Yuglamron said
11:36 AM Oct 4, 2018
Not a good look and as others have said a shade over the fridge area is a good idea and of course the cooling fan to help take the heat away.
I would be looking at putting a metal cover over it instead of the plastic. What springs to mind are the plates you see on Alloy canopies with a T handle to open them. I've seen rectangular ones as well as the triangle versions. If the dimensions were OK. With a few holes as per the original would do the job and hopefully not discolour like the plastic.
Warren-Pat_01 said
12:21 PM Oct 4, 2018
Mamil, Just another thought. My Discovery has a similar cover to yours & I have no idea why there are no slots in the area where yours is burnt. Perhaps it's to keep dust out while travelling - the vent on the Eagle was incorporated in the fridge vent & while it let the hot air out, the vent did show signs of over heating.
I like Yugla's idea of adding some holes or one larger one in the cover & have a sliding-swinging cover over it.
I did have some emails from Dometic (cannot find them at the moment) - they suggested the amount of space the van manufacturers left above the fridge was inadequate but I suppose it's all a compromise - more space for heat movement = less space for storage of our goodies!
Yuglamron said
03:02 PM Oct 4, 2018
I'm not sure if the 3 stainless vent on this website would fit but being stainless the heat may give you some colour change but not to the point it would disintegrate like the plastic will in time.
Mamil wrote: Max daytime temp was about 32deg and that side of the van was sitting in the morning sun, so the gas was on practically non-stop to try and cool the thing down, and the flue vent was getting too hot to touch.
You also say in another reply that your fridge is not working properly. It looks like the gas is working overtime as there is something wrong with the installation. Optimal installation of Dometic 3 Way absorption refrigerators. Download that document. Check that the fridge has been installed as per those instructions. Many of the manufacturers don't install absorption fridges properly. The notice of the gaps between the fridge and the wooden cabinet, fill the gaps with insulation if necessary.
If your fridge is over 100 litres in size then it should be installed as per figure 4. Note the size of the vents in figure 4, many of the manufacturers use the vents as shown in figure 1. I see too many vans when I walk around a park with the small vents on big fridges (it is easy to pick them, small vents that are too far apart for small fridges.)
Another problem is the top vent mounted too low. If you look through the top vent and can see any of the top fins on the back of the van then the vent is too low. If the vent is too low then air can escape out of it without passing through the fins and not contributing to the cooling.
Mamil said
06:57 PM Dec 23, 2018
Resurrecting this thread, because two months on I might have finally solved the puzzle!
The original problem was that my Dometic 3-way fridge wasn't cooling properly on gas, and the external plastic flue vent cover had become discoloured due to getting too hot.
So, I checked out the installation of the fridge in the van with respect to proper sized vents, baffles etc. and it all checked out as a good install.
Then I looked at ventilation, and found it already had one cooling fan as standard, but this wasn't coming on because the location of the thermostat (on the liquid heat exchanger pipe) wasn't getting to the thermostat operating temperature of 70degC.
So, thinking this might be the culprit, I moved the thermostat closer to the boiler where it was getting hotter, and added a second fan to improve the air flow. I also wired both fans into a 3-way switch which allowed me to have them off, on all the time, or operated by the thermostat, and for good measure added an LED indicator light that told me when the fan was operating.
Thinking I had solved the problem, I next set about replacing the discoloured flue vent cover with a new one I'd ordered. It was at this point I noticed something strange. According to the installation instructions of the flue kit there should be a spiral metal baffle inside the flue, part 5 on the diagram, but on mine it was nowhere to be found!
At this point I contacted Dometic technical support again and asked if my model should have a flue baffle. Their answer was that it definitely should, and that it wouldn't work properly on gas if it didn't have one. Bingo! Apparently this $10 piece of twisted metal is critical to the proper operation of the fridge on gas (but not AC or DC), as it slows the passage of the hot air from the gas burner up the flue so that it can transfer more of it's heat to the ammonia solution that is flowing in a pipe parallel to it. If not enough heat gets transferred into the ammonia solution, the absorption process doesn't work effectively. It could also explain why my plastic flue vent cover got discoloured, as the flue gasses were rising too fast up the flue and not giving up enough of their heat to the ammonia solution, they exited the flue still hot enough to burn the plastic cover!
So a few weeks later (after a little mixup on what particular flue baffle was required for my model of fridge) I get a new baffle in the post.
Fitting it only took minutes, and now the fridge seems to be working as designed - even with recent ambient temps in mid thirties it's getting nicely cold on only the middle setting, and cycling on and off like it should. Only an extended trip up north will tell if it's truly fixed, but the signs so far look very promising.
As a footnote, now it's working properly the liquid heat exchanger is getting much hotter, so I've been able to move the fan thermostat back to it's original location and the fan come on when it's supposed to.
Why the baffle wasn't in there in the first place remains a mystery - maybe it wasn't supplied by Dometic, or the installer left it out - I'll probably never know? But hopefully my misfortune may be of help to others. It's by no means the only reason a 3-way fridge doesn't perform, but if you've exhausted the obvious possibilities might be worth checking you have a baffle in there. My baffle was missing in action from new, but they are only thin metal and I've heard they will get eaten away by heat and rust over time so are essentially a replaceable service item, so worth checking on older fridges that aren't performing well.
Anyway, thanks to those who offered advice above, to Dometic technical support for their help, and I hope my voyage of discovery may be of use to someone else someday...
Hi All,
On a recent trip I noticed the plastic cover of the boiler flue vent on my Dometic 3-way fridge has become discoloured from heat - see attached photo. Max daytime temp was about 32deg and that side of the van was sitting in the morning sun, so the gas was on practically non-stop to try and cool the thing down, and the flue vent was getting too hot to touch. Has anyone else had this happen? Is this normal under heavy usage, or indicates a problem? Thanks.
-- Edited by Mamil on Wednesday 3rd of October 2018 09:49:25 PM
-- Edited by Mamil on Wednesday 3rd of October 2018 09:49:41 PM
Is the fridge working ok ie keeping cool in the main section, freezing in the freezer? I assume you were running on gas.
In the temperatures where you are, I would suggest a shade be added to that side of the van over the fridge. See my post in Hints, Tips & Great Ideas for what I did for our previous camper. The flue definitely gets hot - there is a gas burner down at the other end. It has to boil the ammonia solution to cool the fridge down.
Just make sure some enterprising insect has not built a mud nest in the vent holes.
Yes on gas, and no, the fridge was not managing to keep things frozen. So there's no doubt the gas boiler was working hard, and good suggestions on other measures to take to keep it from needing to work that hard, and in fact I've already ordered a fan to force ventilation over the cooling fins. However, point remains that I would have thought flue parts would be designed to take the temperature at max. operating output without starting to breakdown - which is essentially what turning brown is for plastic?
Point to note with fridge is as Warren said keep it shaded from direct sun on that side of van.
Also instead of turning fridge up to maximum turn it down to about 3/4 this allows the fridge to cycle better and as weird as it seems stay colder.
Not a good look and as others have said a shade over the fridge area is a good idea and of course the cooling fan to help take the heat away.
I would be looking at putting a metal cover over it instead of the plastic. What springs to mind are the plates you see on Alloy canopies with a T handle to open them. I've seen rectangular ones as well as the triangle versions. If the dimensions were OK. With a few holes as per the original would do the job and hopefully not discolour like the plastic.
I like Yugla's idea of adding some holes or one larger one in the cover & have a sliding-swinging cover over it.
I did have some emails from Dometic (cannot find them at the moment) - they suggested the amount of space the van manufacturers left above the fridge was inadequate but I suppose it's all a compromise - more space for heat movement = less space for storage of our goodies!
I'm not sure if the 3 stainless vent on this website would fit but being stainless the heat may give you some colour change but not to the point it would disintegrate like the plastic will in time.
https://www.sheridanmarine.com/product/stainless-steel-louvred-vents
You also say in another reply that your fridge is not working properly. It looks like the gas is working overtime as there is something wrong with the installation. Optimal installation of Dometic 3 Way absorption refrigerators. Download that document. Check that the fridge has been installed as per those instructions. Many of the manufacturers don't install absorption fridges properly. The notice of the gaps between the fridge and the wooden cabinet, fill the gaps with insulation if necessary.
If your fridge is over 100 litres in size then it should be installed as per figure 4. Note the size of the vents in figure 4, many of the manufacturers use the vents as shown in figure 1. I see too many vans when I walk around a park with the small vents on big fridges (it is easy to pick them, small vents that are too far apart for small fridges.)
Another problem is the top vent mounted too low. If you look through the top vent and can see any of the top fins on the back of the van then the vent is too low. If the vent is too low then air can escape out of it without passing through the fins and not contributing to the cooling.
Resurrecting this thread, because two months on I might have finally solved the puzzle!
The original problem was that my Dometic 3-way fridge wasn't cooling properly on gas, and the external plastic flue vent cover had become discoloured due to getting too hot.
So, I checked out the installation of the fridge in the van with respect to proper sized vents, baffles etc. and it all checked out as a good install.
Then I looked at ventilation, and found it already had one cooling fan as standard, but this wasn't coming on because the location of the thermostat (on the liquid heat exchanger pipe) wasn't getting to the thermostat operating temperature of 70degC.
So, thinking this might be the culprit, I moved the thermostat closer to the boiler where it was getting hotter, and added a second fan to improve the air flow. I also wired both fans into a 3-way switch which allowed me to have them off, on all the time, or operated by the thermostat, and for good measure added an LED indicator light that told me when the fan was operating.
Thinking I had solved the problem, I next set about replacing the discoloured flue vent cover with a new one I'd ordered. It was at this point I noticed something strange. According to the installation instructions of the flue kit there should be a spiral metal baffle inside the flue, part 5 on the diagram, but on mine it was nowhere to be found!
At this point I contacted Dometic technical support again and asked if my model should have a flue baffle. Their answer was that it definitely should, and that it wouldn't work properly on gas if it didn't have one. Bingo! Apparently this $10 piece of twisted metal is critical to the proper operation of the fridge on gas (but not AC or DC), as it slows the passage of the hot air from the gas burner up the flue so that it can transfer more of it's heat to the ammonia solution that is flowing in a pipe parallel to it. If not enough heat gets transferred into the ammonia solution, the absorption process doesn't work effectively. It could also explain why my plastic flue vent cover got discoloured, as the flue gasses were rising too fast up the flue and not giving up enough of their heat to the ammonia solution, they exited the flue still hot enough to burn the plastic cover!
So a few weeks later (after a little mixup on what particular flue baffle was required for my model of fridge) I get a new baffle in the post.
Fitting it only took minutes, and now the fridge seems to be working as designed - even with recent ambient temps in mid thirties it's getting nicely cold on only the middle setting, and cycling on and off like it should. Only an extended trip up north will tell if it's truly fixed, but the signs so far look very promising.
As a footnote, now it's working properly the liquid heat exchanger is getting much hotter, so I've been able to move the fan thermostat back to it's original location and the fan come on when it's supposed to.
Why the baffle wasn't in there in the first place remains a mystery - maybe it wasn't supplied by Dometic, or the installer left it out - I'll probably never know? But hopefully my misfortune may be of help to others. It's by no means the only reason a 3-way fridge doesn't perform, but if you've exhausted the obvious possibilities might be worth checking you have a baffle in there. My baffle was missing in action from new, but they are only thin metal and I've heard they will get eaten away by heat and rust over time so are essentially a replaceable service item, so worth checking on older fridges that aren't performing well.
Anyway, thanks to those who offered advice above, to Dometic technical support for their help, and I hope my voyage of discovery may be of use to someone else someday...
An excellent out come, great bit of information.
Thank you. Ralph.