17' Series Installing a circulating fan inside Dometic Fridge

Boots in Action · Apr 27, 2017

Drover said:
I bet a few of them are around as well.......................have seen new from factory back of fridge open to under bench space and opening for cables etc not sealed so fridge hardly worked, cupboards nice and warm, bit of tin, can of foam, tube of silastic and all good, freeze lettuce on 3.

Hi Drover, great to be able to do these things and handy enough to be able to put it all back in better condition. Fridge open to under bench cupboards was a problem with my Penguin, but fortunately only at top - bench top got quite warm. Fixed with top baffle made from aluminium sheeting to direct hot air out through top vent. Guess you have seen a lot of things like this during your time. Thanks for all your feedback.

Boots in Action · Apr 27, 2017

Hi @mikerezny , I have finally managed to get some sort of pictures of the melt drain tube on my friend's Dometic fridge. It is a bit hard to see, but basically, the drain tube exits the back of the fridge and is turned down into the metal collector bowl. The tube is then looped in a 360 degree arc and is then directed down and out of the bottom vent. Disregard drain spout still attached to bowl. It now does nothing, but was the cause of a lot of problems. See story on lack of maintenance. A lot (but not all) of domestic home refrigerators have this water lock system, because with the frost free fan running, there is some sort of low pressure inside the fridge at all times, and when you close the door, it increases until reduced by air pressure escaping through water lock in drain tube. Thinking about our heat absorption fridges, if the fridge starts off warmer than the outside air, then as the inside cools (and volume becomes less owing coldness), then air has to come IN somewhere and the open tube at the back would allow HOT air to be dragged in. What do you think about that theory?? Possible?? Good luck.

Drover · Apr 27, 2017

If that was the case then as the freezer gets cold you wouldn't be able to open the door as the pressure would be sucking the door in...............forgot not everyone has a seperate freezer.......So a Mythbusters Plausable I suppose until someone shoots it down, though the fridge door usually gets opened that much it would negate it.

Fun to pull someones stuff apart and actually get it back together and it works, very cool.

Boots in Action · Apr 28, 2017

Drover said:
If that was the case then as the freezer gets cold you wouldn't be able to open the door as the pressure would be sucking the door in...............forgot not everyone has a seperate freezer.......So a Mythbusters Plausable I suppose until someone shoots it down, though the fridge door usually gets opened that much it would negate it.

Fun to pull someones stuff apart and actually get it back together and it works, very cool.

Hi @Drover , one thing you learn very fast - you work on other person's stuff firstly (with all care and NO responsibility!) then work on your own without problems knowing what you did wrong on your mate's stuff! It is very heartening when the whole plan comes together, no parts left over, and it works. Even more reason to have a drink or two if it works better than before. Other motto - "if it ain't broke, don't fix it!". Trouble with that is , you do not know what is "broke" if you don't take it apart first. Aaahhhh - life is full of conundrums.

Boots in Action · Apr 29, 2017

Drover said:
Have had a fan set up to fit since this thread started, runs from the light switch just haven't got to fit it yet, my drain hole is only about 10mm if that, so wouldn't think it would matter but 25mm is a tunnel.

Hello @Drover , have done some more research about reducing airflow in/out of melt water tube. It seems that all the tubes - 10mm, 12mm, 15mm, and even 20mm ID drain hoses all have a plug in the end of them with a small 1mm hole in the plug. This is how they reduce airflow in all the RVs in the US. Not always obvious in pictures, but came across it in a section on maintenance of drain tube. I think the plug would be easily lost in some vans or removed because they would be easily blocked up. They also tend to run the tube into a bowl which is connected to the boiler stack to evaporate the water. Others just run the tube onto the floor - cheap and nasty and likely to cause problems. I think @mikerezny has accidentally stumbled on the similar system of restricting airflow loss in an earlier thread. You learn something new everyday, but one should always get the full story like I have. Sorry for any previous misinformation.

Boots in Action · Apr 29, 2017

Duncanblake36 said:
We'll I'm thinking a terminal switch that makes a circuit when the temp goes below a threshold (eg 8 degrees). This will activate the fans and a led light that will stay on and light up the fridge while the fridge is in operation.

When we are finished with the fridge we turn it off and leave the doors agar and fans and led lighting will turn off once temp gets above threshold.

I need a light and a better solution for the fans.

I'll have a head scratch this weekend and see what I can come up with.

Thinking about it more. A switch may be full (and fool) proof. Dunno where to install it though. I need a place that is out of the way plus easy to mount.[/QUOTE

Hello @Duncanblake36, I would definitely install an inline switch which gives you complete control of fans (and light). When you turn off fridge, you turn off fans/light at inline switch at the same time.us]

Drover · Apr 29, 2017

I think the crud build up would slow things down..........................internal fan for mine is about to have a superior upgrade as I had a light bulb moment today, a cunning plan was devised to improve air movement ...................when I build it I may have to patent it , so if I tell you it may have to be the last thing you hear.

Have read in manuals about the drain set ups like a household fridge, never seen one in the real world, not surprising since the fridges are rarely fitted as per the book and the drain hose goes straight thru the floor...

Boots in Action · Apr 29, 2017

Drover said:
I think the crud build up would slow things down..........................internal fan for mine is about to have a superior upgrade as I had a light bulb moment today, a cunning plan was devised to improve air movement ...................when I build it I may have to patent it , so if I tell you it may have to be the last thing you hear.

Have read in manuals about the drain set ups like a household fridge, never seen one in the real world, not surprising since the fridges are rarely fitted as per the book and the drain hose goes straight thru the floor...

Hello @Drover , don't you ever rest???
You are probably correct again about the crud build up in drain tubes, not to mention the short cuts taken by some manufacturers/builders in just draining the melt water onto the floor or through it with no restriction. Few people would do maintenance or know about it anyway. Refer to my earlier thread about lack of maintenance on friend's van fridge. One of the household domestic frost free fridges I worked on had an "S" bend in the tube that went into the bowl underneath - A General Electric I think.

Now about this "light bulb moment" when you turned yourself on and could see into the future. Does this cunning plan to improve airflow for your fan involve turbo charging or even super charging, maybe greater voltage, or some other devious device?? You can tell me as I can keep a secret (for little while at least) for a small fee. Trust me. I can hardly wait!!

I can see by the latest list of topics covered this week on this forum that you score on several fronts. No wonder you need a rest. A veritable fountain of knowledge on all caravan matters. (I have to cheat by doing a lot of reading and research.) Congrats on doing so much for everyone on this forum.

Drover · Apr 30, 2017

Nah, no font of knowledge here, just been around awhile, see a problem and work out how to fix it.........................so years of reading and lots of time thinking, hanging over a steering wheel for hours on end does that................................just CDF mostly.

Duncanblake36 · Apr 30, 2017

Ok. So this is what I'm thinking. Getting 5 x 80mmx80mm x 10mm CPU fans and mounting them across the top of the blades.
Its 15-20 mm gap so 5-10mm gap for air.
Fans speed will be dialed down with a resistor switch so that the fan speed speed is very low.
Power will be run via the drain hole.
Power will be activated using a thermo switch (on when >50 degrees) on the coil on the fridge heater.

Will that work???

My rational is that it's pushing air through the blades downward so it should flow through to the bottom of the fridge and since its sucking at the top then it should circulate ok.

I was thinking of putting them on side wall but then I'll have to watch what i put on the side shelves of the fridge.

Boots in Action · May 1, 2017

Duncanblake36 said:
Ok. So this is what I'm thinking. Getting 5 x 80mmx80mm x 10mm CPU fans and mounting them across the top of the blades.
Its 15-20 mm gap so 5-10mm gap for air.
Fans speed will be dialed down with a resistor switch so that the fan speed speed is very low.
Power will be run via the drain hole.
Power will be activated using a thermo switch (on when >50 degrees) on the coil on the fridge heater.

Will that work???

My rational is that it's pushing air through the blades downward so it should flow through to the bottom of the fridge and since its sucking at the top then it should circulate ok.

I was thinking of putting them on side wall but then I'll have to watch what i put on the side shelves of the fridge.

View attachment 49121

Well @Duncanblake36 , that is the most sophisticated air movement system that I could ever imagine!! Although the theory of it is sound, but in practical terms, not as good as you should expect with all the work and time - my humble opinion only.
Firstly as @Drover and @Dobbie and @bigcol have said, fans are only to move the air around inside the fridge. Although your idea is to move large amounts of air around at low velocity, there is little need to move that volume in a downwards direction as the colder air normally falls towards the bottom in any case, and slowly soaks the goods with cold, and displaces the warmer air upwards. 5 X 80mm fans will move a lot of air, a bit of an overkill in my opinion. You are correct about air at the top being sucked in, and in theory, it should be the warmest air too. But with swirling currents you are thinking of creating in the fridge with large air movements, will it always be the warmest air there??? Power through the drain tube is probably satisfactory as long as the wires are thin as they should be as very little current is used. A thermo switch on coil of fridge heater is a good idea if you have fans outside to help fridge operate more efficiently. The 50 degree switch is a debatable one as some members on this forum have had various results at different settings. You may have to experiment with different degree thermos to get the best result. I have just ordered 5 of them at 40,45,50,55 and 60 degrees so I can find the best one to suit our climate here in Qld.
Personally, I like the "KISS" system and although the single fan of whatever size on the side wall may not be perfect, I believe it to be both simple AND effective. For more info and other ideas, go to Ebay Aust, type in RV refrigerator cooling. Up will come a whole series of videos. Ignore them at first and type in Fridge fan and baffles. Up will come more interesting choices, but I scrolled down to rv refrigerator fan by Lonney Wade and watched a 5 minute video. Very informative. There are plenty of other choices there also, all of them simpler and cheaper than your complicated suggestion and probably just as good??
Now @Drover and everyone else knows where I get my info from, but always listen to other members' ideas as nothing is as good as experience. Regards

mikerezny · May 1, 2017

Boots in Action said:
I have just ordered 5 of them at 40,45,50,55 and 60 degrees so I can find the best one to suit our climate here in Qld.

Hi
@Boots in Action,
I read some specs on these N.O. thermostats on one of the eBay sites that after they have switched ON, they will switch back off at 15C lower. So, a 40C N.O thermostat will switch on at 40C and then will not switch off until the temperature has gone down to 25C.
So, in summer, even if the fridge is off, it will turn on once the temperature goes above 40C and will not switch off again until it has dropped below 25C. That could be problematic if the battery is left switched on when the van is stored.

I also remember @Drover saying that for correct operation, the fins had to be at least 50C. Maybe I misunderstood. If not, then the lowest rating thermostat would be 65C. It prompted me to think that I might want to increase my thermostat from 50C to 65C.
Unfortunately, I only ordered 50C, 55C, and 60C, So I would need to buy the 65C.

But it is winter and I am lazy. So I probably just leave it the way it is. If it ain't broken don't fix it. I will just wait until it dies and replace it with either the 55C or 60C ones I already have.

cheers
Mike

Duncanblake36 · May 1, 2017

Keeping it simple.... I've over thought this so much its doing my head in.
I think I'm just going to move the existing fan that I have to the side wall (on an angle) so it pushed the air across the fins and see how that goes.

Thanks for the info though boys. @Drover @Boots in Action @mikerezny

I'll keep it in mind for next summer.

mikerezny · May 1, 2017

Duncanblake36 said:
Keeping it simple.... I've over thought this so much its doing my head in.

Hi @Duncanblake36,
yep, my thoughts as well.

cheers
Mike

Boots in Action · May 1, 2017

mikerezny said:
Hi
@Boots in Action,
I read some specs on these N.O. thermostats on one of the eBay sites that after they have switched ON, they will switch back off at 15C lower. So, a 40C N.O thermostat will switch on at 40C and then will not switch off until the temperature has gone down to 25C.
So, in summer, even if the fridge is off, it will turn on once the temperature goes above 40C and will not switch off again until it has dropped below 25C. That could be problematic if the battery is left switched on when the van is stored.

I also remember @Drover saying that for correct operation, the fins had to be at least 50C. Maybe I misunderstood. If not, then the lowest rating thermostat would be 65C. It prompted me to think that I might want to increase my thermostat from 50C to 65C.
Unfortunately, I only ordered 50C, 55C, and 60C, So I would need to buy the 65C.

But it is winter and I am lazy. So I probably just leave it the way it is. If it ain't broken don't fix it. I will just wait until it dies and replace it with either the 55C or 60C ones I already have.

cheers
Mike

Thanks for the update @mikerezny . I knew there was something on this forum about the operation of these thermo. Looks like I am going to start with a 60 degree one as suggested by @Drover and see how it goes for me, although I can then work lower as necessary. Will be able to test same in the next few weeks even though it is winter here and be able to confirm some ideas.

Duncanblake36 · May 2, 2017

This is a good article
http://www.dreampod.net/boroma/fridgefan.html
I would go with a 60 degree thermo switch though - Even a 50 would be fine (for us Victorians) as I doubt if it would get that hot when the van is not in use.

Boots in Action · May 2, 2017

Duncanblake36 said:
This is a good article
http://www.dreampod.net/boroma/fridgefan.html
I would go with a 60 degree thermo switch though - Even a 50 would be fine (for us Victorians) as I doubt if it would get that hot when the van is not in use.

Hi @Duncanblake36 , Fortunately with my setup, I have an inline switch with which I can over-ride the thermo, so no hassles even if van not in use. I really do like the article you have given me to follow up. The positioning of the thermo was something I did not know, so now that is not a problem. I have two separate circuits for my internal fans and my external fans, both with manual in line switches. At this stage, I will only be installing a thermo for the outside fans.
Going away to the Connondale ranges tomorrow so another good time for testing. Temps expected to be between 26 degrees max and 15 degrees min, so should be easy street.
As @Drover says, "you are never too old to learn something ..........". I think my offer of "only a fool thinks he knows everything!!" is more to the point. Thanks again for your article.

Drover · May 2, 2017

That's a good article @Duncanblake36 , have to save it so we don't have to repeat the same thing in another thread when this gets rehashed again........its just what's been said in a couple threads over the last few years.

Boots in Action · May 2, 2017

Drover said:
That's a good article @Duncanblake36 , have to save it so we don't have to repeat the same thing in another thread when this gets rehashed again........its just what's been said in a couple threads over the last few years.

Great idea @Drover. I have already saved it. What do you think of a 70 Degree thermo for us in sunny and sometimes hot Queensland??

Boots in Action · May 23, 2017

Hi @mikerezny , your info about the "range" of operation of NC thermostats is very intriguing and valuable. I have just spent a week in the Connondale ranges at an elevation of 600 metres. The air temperature for those days varied from max 26 C during daytime and down to 4 C in the morning, both shade temperatures. I used a Technitherm metal backed thermometer to measure the heat coming off the fins of my refrigerator running on gas. Placed just where thermo would be and as close to tubing as possible. There were some surprising results!! At an ambient temp of 26 C, the fins temp was as high as 85 C but dropped down to 35 C after 2 minutes with fans on. Other times at 20 C ambient, the temp still reached more than 75 C, but dropped quickly to about 32 C with fans on for a very short time. At first thing in the morning (ambient 4 to 5 C), the temp was only about 38 C, without fan cooling!! Apparently, the colder night air movement through the back was sufficient to keep radiating fins cool. Me thinks that a 50 C thermo may be the way to go. I will do further testing next time out with varying temps to check readings. Thought you may be interested as it CAN get cool up here in winter.

mikerezny said:
Hi
@Boots in Action,
I read some specs on these N.O. thermostats on one of the eBay sites that after they have switched ON, they will switch back off at 15C lower. So, a 40C N.O thermostat will switch on at 40C and then will not switch off until the temperature has gone down to 25C.
So, in summer, even if the fridge is off, it will turn on once the temperature goes above 40C and will not switch off again until it has dropped below 25C. That could be problematic if the battery is left switched on when the van is stored.

I also remember @Drover saying that for correct operation, the fins had to be at least 50C. Maybe I misunderstood. If not, then the lowest rating thermostat would be 65C. It prompted me to think that I might want to increase my thermostat from 50C to 65C.
Unfortunately, I only ordered 50C, 55C, and 60C, So I would need to buy the 65C.

But it is winter and I am lazy. So I probably just leave it the way it is. If it ain't broken don't fix it. I will just wait until it dies and replace it with either the 55C or 60C ones I already have.

cheers
Mike

17' Series Installing a circulating fan inside Dometic Fridge

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