Dometic 3- Way Fridge

[Bud]

IMPORTANT, CRITICAL:

Don't listen to InterBlog,Me or anyone else concerning absorption refers, Period. James knows what the heck he is talking about. 7:05

https://www.youtube.com/watch?v=AcOxW45sQxo

Bud

[InterBlog]

Originally Posted by Bud

IMPORTANT, CRITICAL:

Don't listen to InterBlog,Me or anyone else concerning absorption refers, Period. James knows what the heck he is talking about. 7:05

Ah, thanks for that! That was unexpected!

[booster]

It is kind of interesting about the driving issues, as we have always heard of frigs warming up while driving, but it almost always attributed to airflow issues from the van motion and aerodynamics. Many driving heat up issues were fixed with air baffles, deflectors, fans, etc over the years, that we have heard about.


It has also been stated many times in lots of places over the years that absorption frigs actually work better while driving because the motions help refrigerant draining in the condenser. Exception often noted about a sustained long climb, but it would have to be pretty long and steep to be significant, I think, to violate the acceptable level specs.


Doesn't matter either way for us with compressor frigs, but interesting anyway. I do know for certain we will never go back to an absorption frig unless there is some revolutionary design improvement that makes all the weaknesses go away.

[markopolo]

Air circulation would be affected by driving.
Affect air circulation and cooling is affected.
Affect cooling and propane use is affected.

Running an absorption fridge on AC through an inverter while driving is an option if greater cooling is required. (haven't read the entire topic so probably already mentioned)

[jrobe]

One general refrigerator lesson we learned over the years is that bigger is not always better. We don't need enough cold beer, pop and milk in the refrigerator for 1-2 weeks like at home. All we need at any one time is enough food and drinks for 1-2 days and then slowly replace items as need. It just takes a few seconds to add some cans of warm drinks from the closet in the evening to prepare for the next day. A bigger refrigerator just creates energy problems and takes up valuable interior space.

Our current RV has a small, very efficient compressor refrigerator that takes almost negligible power. Managing the refrigerator never enters my mind anymore.

[avanti]

Originally Posted by jrobe

One general refrigerator lesson we learned over the years is that bigger is not always better.
...
A bigger refrigerator just creates energy problems and takes up valuable interior space.

I don't disagree, but the other side of the coin is that refrigerators work better when there is space for air flow inside the fridge, lest you get hot and cold spots. Those interior fans that people like so much won't help much if there is no room for air flow.

Also, we find the ability to carry a week or two's worth of frozen pre-prepared meals in our freezer to be a great luxury.

[booster]

Originally Posted by avanti

I don't disagree, but the other side of the coin is that refrigerators work better when there is space for air flow inside the fridge, lest you get hot and cold spots. Those interior fans that people like so much won't help much if there is no room for air flow.

Also, we find the ability to carry a week or two's worth of frozen pre-prepared meals in our freezer to be a great luxury.

Since we have limited space for a bigger frig in our Chevy Roadtrek, just like the Mexican Dr, we have learned what we can carry for how long and so far have been able to work around that without issue to this point. I think if we were looking at stocking up frozen foods for a longer trip need, I would get a BD35 cooled travel box that can go to freezer settings. Those tend to be top cover and quite efficient because of the better sealing that way for the most part. That way it could be out of the way and not accessed except to transfer a few items to eat or to the main frig. When empty it could be taken off line and save the power.

[Rlum]

Hi: Anyone look at converting their 3 way refrigerator with a compressor kit from Nova Kool. Several other companies have such products. I read/saw photos of two people on Travato forum(Facebook) do this. Cost around 1K. Looks like it can be DIY project.

I am one of those Dometic RML 8330 3 way refrigerator. It is working fine but when temps get up into 100 plus, it really cannot keep up. I have multiple fans inside and outside. Just something to consider.

Thanks

[ChicagoTom]

Mine works great. Fan pointed at evap fins, ( INTERIOR FAN!) I keep posting, and those who listen have sent me feedback on how what a difference it's made. Others hype about exterior fans, and this is just such a simple solution, but then again, most don't like simple. LOL

[mkguitar]

Originally Posted by InterBlog

We would fill our tank (Manchester #6813, 5.5 gallon capacity) before leaving Houston, and by the time we got to Bangor three days later, we'd have just 1 gallon of propane remaining!

I run on DC when driving.



I don't think I'd be able to maintain a flame on the road, I don't have a baffle system




Mike

[InterBlog]

Originally Posted by mkguitar

I run on DC when driving.

I don't think I'd be able to maintain a flame on the road, I don't have a baffle system

Mike

I have no doubt that we had an uninterrupted flame. We always travel in August, through the deep south. If the flame had not been maintained, it would have been 94 in the fridges instead of 44.

I don't know how it might be demonstrated that the inefficiencies are caused by disrupted circulation in the ammonia rather than some issue with air flow. I don't have absolute proof that's what it was.

But if air flow was a primary problem, mightn't a sustained wind also be expected to have some kind of impact on efficiency? I've been parked overnight in storm conditions when the van was utterly pummeled by wind. I noticed zero impact on the 3-way fridge.

[booster]

Originally Posted by InterBlog

I have no doubt that we had an uninterrupted flame. We always travel in August, through the deep south. If the flame had not been maintained, it would have been 94 in the fridges instead of 44.

I don't know how it might be demonstrated that the inefficiencies are caused by disrupted circulation in the ammonia rather than some issue with air flow. I don't have absolute proof that's what it was.

But if air flow was a primary problem, mightn't a sustained wind also be expected to have some kind of impact on efficiency? I've been parked overnight in storm conditions when the van was utterly pummeled by wind. I noticed zero impact on the 3-way fridge.

I think the wind issue would totally be where the wind was coming from and how it affected the air pressure at the inlet and out vents. It could make it better, worse, or no effect based on what I saw on our old frig.

[GallenH]

Originally Posted by Rlum

Hi: Anyone look at converting their 3 way refrigerator with a compressor kit from Nova Kool. Several other companies have such products. I read/saw photos of two people on Travato forum(Facebook) do this. Cost around 1K. Looks like it can be DIY project.
I am one of those Dometic RML 8330 3 way refrigerator. It is working fine but when temps get up into 100 plus, it really cannot keep up. I have multiple fans inside and outside. Just something to consider.

I've heard about those as well. I'm not sure that the cost difference between that and a new compressor unit is worth it. It may be. To me the fridge cost is a lessor fraction of the total cost it will take to upgrade the electrical, both storage and charging.

As I mentioned on this or another thread I'm getting ready to go up to the higher elevations in Arizona....tomorrow!...and have started my old Dometic 3-way on 120v in preparation. I started it last night and have been keeping readings on outside temp and fridge temp. So far I've been observing a differential of 57 degrees which sounds great.....but in Phoenix where it's 100+ that means fridge is running in low 40s. But in the morning where it's "only" 80-degrees (yes, that's Phoenix) it's good. High country right now gets up to the low to mid 80s. I plan to keep taking readings.

[nicaland]

I finished my fridge mod, detailed below, on my Dometic RM 2310 equipped Xplorer 230XLW last March, but waited until I knew I could get a couple of 100 degree or so days in a row to report the results which are posted at the end of this reply.

Immediately after finishing the project though, after running the fridge all night with all 5 fans running at full speed and max cool setting using AC power, at noon and a 76 degree ambient temp and the van parked under a carport, my freezer was at -10 degrees (F) and the fridge section was 28 degrees! A test run on the following day using propane produced virtually the same results. I never use DC so didn't bother to test with it. It did get down to 48 ambient both nights, which of course helped this thing to get so friggin cold.

So here are my mods:

First order of business was to eliminate the gaps between the top and sides between the fridge and the enclosure, and do it in a way that encouraged laminar airflow. I used 28 gauge galvanized sheet metal, and after careful measuring and cutting, it was literally a snap-in fit.


[IMG]fridge mod 1 (1280x713).jpg[/IMG]
[IMG]fridge mod 2 (1280x960).jpg[/IMG]

Then I placed another piece of sheet metal to run from the inside of the top of the lower access door, curving up to and laying against the condenser cooling fins. This was also cut to be a snap-in fit. I had to notch the van's body so this piece was wide enough to cover the entire fridge back from side to side, but this was covered by the exit grill after installation. The first pic below, taken from the top exhaust vent area looking down, shows where this sheet is in contact with the fins, and the second one was taken from the lower access/intake door looking up. With both of these sheets installed, every single bit of air entering the lower intake grill is now forced to run through the condenser cooling fins, and in a nice laminar fashion.

[IMG]fridge mod 4 (1280x960).jpg[/IMG]
[IMG]fridge mod 9 (1280x960).jpg[/IMG]

I then cut a piece of 1/2" polyiso aluminum back foam board to fit in between the lower/outer plenum sheet and the van's exterior skin as an aid to reduce solar heating of this space, with the bottom of it resting at the top of the lower intake grill and the top of it cut to fit so the fan housings would rest on top of it. Then I mounted the fans to the inside of the exhaust grill with zip ties, and added another piece of polyiso below them that both covered all of the exhaust area except for what flows through the fans, which when installed also doubled the thickness of the previously installed polyiso in that location. The fans at 3.24" square were literally a perfect fit for my installation, are really very high quality, and were ridiculously cheap, $19 for all five of them! here's an Amazon link: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
And here's a link to their product spec page: https://www.arctic.ac/us_en/f9.html

Their power draw is also ridiculously low at .16A @12V and 1800RPM each, or a total of .8A when all five are running at full speed. I have found that running them at around half speed is usually more than sufficient, where they are pulling about .5A. I ganged the fans together with this five way splitter. it is a four pin splitter but the three pin connectors on the fans still fit perfectly.
here's an amazon link to it: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Pics:
[IMG]fridge mod 13 (1280x960).jpg[/IMG]
[IMG]fridge mod 15 (1280x960).jpg[/IMG]

To turn the fans on/off and control their speed I bought this PWM controller:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
This provides a stepless speed control, is tiny, cheap, and even has a red LED that increases brightness with speed dialed in. Great little night light!

Pic:
[IMG]fridge mod 17 (1280x960).jpg[/IMG]

So a few days ago we hit the century mark here for two days and 98 the next. Parked outside East-West with the fridge side getting sun all day, following the same start up as above, at 2:00 PM and 99 degrees ambient (air-con off and windows open), all installed cooling fans on half speed and max cool AC power, the freezer was at -2 and the fridge at 38. The following day, at 100 degrees ambient, all the same except running on propane, the freezer was still at -2 but the fridge rose to 40. Could have simply been heat soak that made this minor difference. The third day, at 2:00 and 98 degrees ambient, running propane at full cold and the fans OFF, the freezer rose to 2 degrees F and the fridge rose to 44. This result tells me that my plenum improvements possibly made the biggest difference, and that the net free area reduction of the fans not spinning made little difference in airflow.

Before these mods, a 100 degree full sun day and the fridge on full cold, I would usually see numbers around 32-34 degrees in the freezer and 55-57 in the fridge, so needless to say, I am stoked!

I used to run the fridge on propane while on the road, turning it off at the pump, but now run it on 120 VAC using a 2000W pure sine wave inverter that's connected via an auto-transfer switch to all ac outlets. I still run it on propane while boondocking even though I have a 220 AH flooded deep cycle house bank and 190 watts of solar because it just sips propane and I don't have to worry about too many cloudy days. A $20 tank fill lasts me for 6 weeks or more.

Finally, I hope that all of my photos and external links work! This is the first time I have tried to include them in a post, and I had one hell of a time figuring out how (fingers crossed) to do so, so please advise if you can't see this stuff.

[GallenH]

Very nice job! My mods are modest compared to yours. But it appears that you've covered all the bases nicely. Congrats.

[nicaland]

Thank you GallenH. I'd like to add that the temps I reported, ambient, freezer, and fridge, were not exaggerated at all and were verified by me using both old world and electronic thermometers. Some of the posts that I have read in this discussion in regards to absorption fridge performance mods are, to put it kindly, rather questionable. For example, the idea that this type of refrigeration can be enhanced in RV's that lack the natural draft stack effect present in any RV that does not have the exhaust extending through the roof can be solved by simply adding an internal fan of any type does absolutely nothing to solve the inherent lack of stack height. These things are great if you need to reduce frost buildup on the fridge cooling fins, but that's it, period. Don't waste your money folks on this type of fan if you have a side exhaust absorption fridge and it's not getting cool enough in high external temps. Additionally, as some have pointed out, an axial flow fan, even the marginally ducted axial fan that is used in these computer fans, will most definitely draw recirculated lower pressure air that surrounds it if it is capable of finding such air, hence the importance of eliminating that possibility as much as possible. And finally, these fans do a MUCH better job of pulling rather than blowing air, so if you want to get your money's worth use them as exhaust rather than supply air. When was the last time you saw a computer fan that was blowing air in rather than sucking it out? Induced airflow will always outperform forced airflow. The total cost for the modifications that I made was $34, and three hours of my labor; I admit to having the polyiso board and sheet metal scrap hanging around the garage, but both could still be sourced very cheaply. I've seen interior circulation cooling fans costing more than that.

[engnrsrule]

Wow, so many interesting points in the last few posts...

While I have not observed any decreased performance when driving and running on propane, I usually will run on 12v when underway. The dometic does pull too much amperage to run 12v boondocking. I also believe that wind could impact the performance driving on propane.

I agree that the placement of 1 or 2 computer fans is less than optimum and would pull some air from the adjacent open space of the grill. That is why I increased to 4 fans which approximately cover almost all the open grill area. However, there is also natural induction taking place, so the fans exhausting at the top grill are working with, not against natural convection. To put the exhaust at the bottom, in comparison would be pitting induction against the forced flow and would not be recommended. The baffle serves to direct all air entering the bottom up and thru the fins instead of around them. Induction, or chimney effect or draw is certainly improved with stack height, but I do not think designers are counting on any draw occuring in arrangements of 2 grills less than 3 feet apart. I also doubt if stacks running 8 or 10 feet of RV height would induce that much draft that they would not benefit from some forced boost. So another parked day in the 90s running on 110 and my fridge went to 29 degrees and I had to turn the thermostat up! This I can live with.

I am up to about $60 spent - 4 fans, the thermostatic switch, the spdt switch, the internal battery fan and the wireless thermometer.

[mkguitar]

Originally Posted by GallenH

...and have started my old Dometic 3-way on 120v in preparation.

suggest propane if you have the option

and turn on the roof a/c overnight to get the cabin down to mid 70's


110º tomorrow- enjoy your trip


I believe 87 still closed between Shea and 188
for Bush fire

expect heavier traffic on 60, 17 and 93, 89 and 260- 188 is reopened as of now but...


10pm news says forest service may be shutting down forest access...no details




Mike

[engnrsrule]

Mike,

I like the idea of hardwiring a 12v fan in the fridge. I have 2 fans. The valterra "box" works OK and the batteries last a long time, but I have a larger "desk" fan that moves alot more air and is noticeably better at keeping the fridge cool. I get 3-5 days on a pair of D cells.

I am curious on where to tap 12v and the path to run it into the fridge. This is a Dometic 4 cuft 3-way.

[peteco]

Originally Posted by engnrsrule

Mike,

I like the idea of hardwiring a 12v fan in the fridge. I have 2 fans. The valterra "box" works OK and the batteries last a long time, but I have a larger "desk" fan that moves alot more air and is noticeably better at keeping the fridge cool. I get 3-5 days on a pair of D cells.

I am curious on where to tap 12v and the path to run it into the fridge. This is a Dometic 4 cuft 3-way.

Run power wires up the drain tube.