You think I could answer this with google but I'm not finding the right answers.
The back story. My Thetford 3 way Climate T model fridge works fine on 240v, gas, and maintains temp reasonably well on 12v. But to run it all efficiently I really want to know how each mode works. I'm not sure if I have an issue or not. I put a thermostat in the fridge to monitor temp. If I'm going away I put the fridge on 240v for 24hrs, put my cold food in and switch to 12v just as we're leaving. Drive 6hrs say, and temp may have gone up a few deg but still cold. Then when I switch to gas, the temp steadily climbs for many hours til the gas starts to take effect. Is this normal? This is why I want to understand how the fridge works mechanically.
I understand the fridge is a heat exchanger and Ammonia transforms from liquid to gas as it cycles but do all 3 power input sources heat the Ammonia at the exact same spot. I see where the gas flame sits, but don't know where the 12v and 240v elements are. If they are in different areas, is this why there is a lag in the cooling when I switch to different modes?
First the fridge has to be installed correctly NOT how the van maker does . Distance between back of fridge and wall is specified by fridge maker Bottom and top duct work is critical Fit fans to top mounted condensor highly recommended and duct to top vent semi auto
Connection Issues canbe had with selector control and thermostat Not all power sources use the above
Little voltdrop for 240v and 12v is critical measure at burner elements
FULLY service gas side
gas pressure checked at burner flu internally clean flu lift out internal spiral clean jet clean and burning a good colour FLU hot air director in place to eject hot air from top of flu and prevent recirculation of hot air ignitor gap set up
U need a copy of the manual will answer many of your questions
The electrical elements should be in direct contact with fluid filled boiler
-- Edited by swamp on Saturday 9th of March 2019 05:49:30 PM
Bernie, I can't explain why there is a lag in operation after you switch from 12V operation to gas, but I can answer your question about the positioning of the three heating sources. They are all arranged around the boiler tube, with the gas flue running up parallel for most of the length of the boiler, and the 240V and 12V heating elements slotted into tubes welded onto the bottom portion only. The whole lot is then wrapped in insulation and with an outer metal cover, commonly cylindrical.
Here's a cutaway picture which shows how they are arranged. The boiler tube is black, gas flue green, and one of the slots for a heating element in red. In a fridge like yours that has both 12V and 240V electric heating elements there are two of the red tubes and the heating elements slot into them.
As they are all pretty much in the same location I don't think the position of the heating elements can be the reason for your observation. And, I can't say I've noticed it happening on mine, but then I haven't looked into it in detail. I'll have to check next time I finish a long journey on 12V and switch to gas operation!
Good replies so far. I would add that traditionally the 12V supply leads are undersized so running on 12V does not work well. I replaced them on mine with heavier wires and it improved the performance by a great amount. This fact is well known for 3 way fridges.
As far as the gas goes I would suggest you service the burner as swamp has said.
Jaahn
-- Edited by Jaahn on Sunday 10th of March 2019 10:39:03 AM
Ok. Thanks for the replies. Thanks Mamil, at least now I have some idea of what it all looks like. Thanks Jaahn and Aus-Kiwi, the cable from the Anderson plug to the Omegalec Controller is fairly solid and than it's only 1.5m to the fridge from Omegalec and that cable is ok too. I did measure 12v at back of fridge a while ago but I will re check when I hook the car back up. I changed the output at the Omegalec so fridge won't switch to house batteries if car is stopped. The drain on my 1 house battery would kill it in no time. The gas works great, it just seems to take a while to have effect once I switch across from 12v. I had frozen ice cream in freezer on gas for days and went to 12v for a 6hr drive home and it was rock hard when we got home. Warm day too.
So Swamp, that list of gas service looks like lots of work but keen to learn. I've attached a photo of where I've got to so far. I marked some bits with red. My Manual was not to helpful. I undo 1 from 0 and slide out 3, to start with and clean. Is that right?
1st shows looking onto flu after I removed the bend that exits the van. Not sure what that metal wire does at top of flu stack.. I can jiggle it but can't remove it.
2nd shows a good blue flame making a small round metal gauze glow orange.
Also. Last trip I removed a bit of carbon build up off igniter and pilot lights easy now.
1st shows looking onto flu after I removed the bend that exits the van. Not sure what that metal wire does at top of flu stack.. I can jiggle it but can't remove it.
2nd shows a good blue flame making a small round metal gauze glow orange.
Also. Last trip I removed a bit of carbon build up off igniter and pilot lights easy now.
Metal wire in top of gas flue suspends the "helix", "flue baffle", or "internal spiral" as Swamp called it, in the gas flue. It looks something like this...
It's purpose is to slow and 'twist' the flow of hot gasses as they rise up the flue so they give up as much as possible of their heat to the ammonia solution in the boiler. If this is corroded away it is one reason for poor performance of the fridge on gas, but as you're not getting that then it's likely in good condition. On my fridge the installer left this baffle out completely - but that's another story for another time...
-- Edited by Mamil on Sunday 10th of March 2019 11:03:26 PM
"FLU hot air director in place to eject hot air from top of flu and prevent recirculation of hot air"
I guess these photos are the Air Director and they are very clean and in position.
Hmm, I'm not an expert on these things by any means, but that looks a bit suspect, like someone has bent a tube to fit where it didn't! The standard flue top arrangement is straight up, then a T where one side is open and the other exits the side of the van - see Dometic diagram below. Yours is missing the 'T' piece, number 1 on the diagram, and the top of the flue has just been stuffed into the exit pipe. What effect, if any, this might have I can't tell you, but someone else on here might know, or talk to a qualified fridgie or call the tech support line for your fridge manufacturer and ask them if it's a problem or not.
-- Edited by Mamil on Sunday 10th of March 2019 11:05:24 PM
Thanks Mamil. I'm getting a much better understanding of how these fridges work.
I'll run my fridge on 240v today and then switch to gas after it's cold. It sounds like I should not see any great lag in the gas taking over the cooling duties? Maybe with arriving at a camp site and switching to gas, there's a lot more activity with the fridge being opened and closed, and that's why I'm seeing the temp go up before it settles back to an acceptable temp. Because it seems the 3 ways are working ok.
Years ago I ran our fridge via our computer's UPS which tracked energy consumption every minute of the day. Opening the fridge increases energy consumption a lot & the fridge has to catch up. Opening the fridge many times during a meal & it will give energy consumption a hammering.
Work out all the things you need from the fridge before opening it. Put all the things back together if you can or in say two batches.
Have an official fridge door opener so you have extra hands.
If you can't add extra insulation to the sides at least add it to the door.
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and this is exactly the reason I just stuck a 12v compressor fridge in there.
Going to need to pick up a second battery though.
I was getting sick of the old fights and it just not working properly at the best of times.
Add in a hot day and it's all over.
As When said, opening the fridge causes it to struggle. I have a fridge in the van to use and that requires me to open it up to get stuff out.
A fridge aint much good if you can't open the door.
the 12v is obviously the same and this is a failing of the upright fridges vs a box type set up.
I've considered trying to make some sort of wall for the lower section of the fridge to try and hold the 'cold' in a bit more.
the idea is as far as I've gotten with that one.
Well I did the test and got fridge down to 10deg on 240v and switched to gas. Temp kept dropping down to 6deg and I turned it off. So it all came down to the door being opened too much. That's ok. Now I know and funnily enough, I had already started to think that a perspex sheet at the bottom might help trap air when the doors open, and now read Aus-kiwi has already done just that. I've learnt a lot and am now comfortable with my understanding of how to use a 3 way fridge, I hope.
@Denmonkey. I already see that there must be an endless debate about 3 way vs Compressor fridges. I'm sure many have switched to compressor, only to find a whole new set of problems while others probably found happiness. I don't want to stir that pot.
The T piece attached to the top of the flu does 2 jobs .
1/ flu ingests cold air and mixes //lowers temp of hot air exiting the van
2/the mixing of hot air and the cold air together may speed up the air flow out of the body mounted outlet .
The burner will have a jet inside it . Depends on design the jet either could be accessible in-situ or the burner assembly might require removal . Always leak check with soap suds after reassembly.
If the flame is a good colour leave it alone.
Need pictures of the upper and lower vent position in relation to fridge and van . The upper exit could be a more direct route for airflow exit p of condenser to upper vent. Look up dometic 90ltr fridges they have pics of duct work .
Well I did the test and got fridge down to 10deg on 240v and switched to gas. Temp kept dropping down to 6deg and I turned it off. So it all came down to the door being opened too much. That's ok. Now I know and funnily enough, I had already started to think that a perspex sheet at the bottom might help trap air when the doors open, and now read Aus-kiwi has already done just that. I've learnt a lot and am now comfortable with my understanding of how to use a 3 way fridge, I hope.
@Denmonkey. I already see that there must be an endless debate about 3 way vs Compressor fridges. I'm sure many have switched to compressor, only to find a whole new set of problems while others probably found happiness. I don't want to stir that pot.
Glad you found the problem. I did a test a couple of weeks ago how long it would take the fridge to get back to temperature after opening the door once, very briefly. It took over an hour!
-- Edited by Mamil on Monday 11th of March 2019 11:05:32 PM
@Denmonkey. I already see that there must be an endless debate about 3 way vs Compressor fridges. I'm sure many have switched to compressor, only to find a whole new set of problems while others probably found happiness. I don't want to stir that pot.
All good there mate. I'm happy to discuss or debate a subject without getting bent out of shape
I never take words on a screen personally.
Just throwing out my experience in case it helps some.
I think some sort of panel in the front might help some, plus I've got just the right stuff squirreled away in the shed....i knew it would come in handy for something, despite being told I should bin it years ago.
@Swamp
"The T piece attached to the top of the flu does 2 jobs .
1/ flu ingests cold air and mixes //lowers temp of hot air exiting the van
2/the mixing of hot air and the cold air together may speed up the air flow out of the body mounted outlet ".
Think I'll just leave it like it is but I know if I'm having issues that this may need looking into.
@Swamp
The burner will have a jet inside it . Depends on design the jet either could be accessible in-situ or the burner assembly might require removal . Always leak check with soap suds after reassembly.
If the flame is a good colour leave it alone.
The first photo I attached I put some markings on the parts. Can you guide me in to which bit has the jet inside. Also, the flame is nice and blue,as per the photo. I think that's the right colour,right?
HI
No I am not familiar with your exact burner assembly
@Swamp
The burner will have a jet inside it . Depends on design the jet either could be accessible in-situ or the burner assembly might require removal . Always leak check with soap suds after reassembly.
If the flame is a good colour leave it alone.
I would suggest u take it to a specialist if u donot have the experience on the tools . Its fairly basic operation but i`m considering your safety.
A good manual and some basic thought is all thats needed .
By installing correct duct work at the top vent this will help . The cavity above the fridge boiler assembly is to big an area . A big heat storage area .
maybe another thing to consider, when on 12v the van is moving. this may improve the efficiency of the air flow behind the fridge. When you stop maybe the gas heat has to setup the air flow behind the fridge. I have no idea really but it is a theory .Also I think when on 12v the thermostat does not work.
-- Edited by grahamg on Saturday 23rd of March 2019 09:59:43 PM
As it happens I was checking out the voltage drop on my fridge circuit this afternoon, and the results are interesting.
Voltage at the car battery is 14.0V. By the time it gets to the input of my DC/DC charger in the van it's dropped to 13.1V and that's even though the whole wire run from car to van is in 16mm2!
The DC/DC charger does it's job and boosts the voltage back up to 14.3V, but by the time it reaches the back of the fridge it's dropped again to 12.2V.
So, even though I have nice thick cable and a DC/DC charger to boost the voltage I'm barely getting acceptable voltage at my fridge when running on DC from the car. Imagine what it'd be like with the standard car/caravan wiring and no DC/DC charger - no wonder people find their fridges don't perform on DC!
