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Old 08-24-2020, 05:08 PM   #1
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Dometic Refrigerator Conversion

We have a 12 year old Dometic Absorption Refrigerator, RM3762LB, in our 12 year old Sabre 5th wheel. It has gotten tired and is taking longer to cool down and has more trouble keeping cool on hot days.

We are considering replacing the refrigeration unit with a 12volt compressor style retrofit from JC Refrigeration. https://jc-refrigeration.com/product...-5a-90w-12v-f/

Does anyone have any comments on this type of conversion that they would be willing to share? We are still researching.

Thanks for your help.
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Old 08-24-2020, 05:35 PM   #2
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Unless you are plugged in every night you may want to still run on propane. 12 volt only will eat up your battery fairly quickly.
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Old 08-28-2020, 03:27 AM   #3
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Quote:
Originally Posted by 2007 Sabre RnR View Post
We have a 12 year old Dometic Absorption Refrigerator, RM3762LB, in our 12 year old Sabre 5th wheel. It has gotten tired and is taking longer to cool down and has more trouble keeping cool on hot days.

We are considering replacing the refrigeration unit with a 12volt compressor style retrofit from JC Refrigeration. https://jc-refrigeration.com/product...-5a-90w-12v-f/

Does anyone have any comments on this type of conversion that they would be willing to share? We are still researching.

Thanks for your help.
Others probably know a lot more about this than I do, but it seems the 7.5A draw on this conversion kit is a little higher than just replacing the entire unit with a newer lower amp dedicated compressor fridge. There may be some advantages in going that route.

I just looked at a dedicated compressor 10 cu ft unit that came up on another thread:
https://www.etrailer.com/RV-Refriger...cc-onlyreviews
and it only draws about 3A after a quick-cool-setting start.

This may not make a lot of difference for you if there is always a 110v source handy, but sans propane option if boon-docking, a straight electric will likely cause a daily charging need for the house batteries. Ideally, in such a case, you might have a solar set-up to mitigate this while boon-docking.

The cost for a more efficient replacement refrigerator, plus the solar set-up vs propane, rises over and above the cost for your proposed conversion kit. Plus generator and generator fuel (albeit which may actually use less propane than the old fridge).

There are some advantages to the propane fridge, but there are also some advantages to a compressor fridge. By your post, you probably already know this, but here goes anyway.

First of all dedicated compressor fridges are larger inside for their footprint. In your proposed conversion you won't gain that. Another reason, compressor fridges of all kinds don't need to be so level, a possible reason the old fridge is wearing out. I think(?) the old absorption fridges have a tendency to sustain more of the slowly accumulating boiler damage from less than perfect level. But the compressor fridges need more amperage some say. Still, the old fridges still used about a third of the 12v power the compressor types do, just to operate the propane control... plus add the propane energy yet.

The price of solar is coming down and the sun is free, or at least until some government bean-counter, or the campground, finds a way to tax it. Compressor fridges are even more maintenance free than propane. They cool quicker, meaning they don't need pre-cooling before loading. And of course they better resist getting too warm when the door is opened frequently. And you never have to look to see what they are running on... unless the light doesn't come on when the door is opened, or a power alarm goes off.

My dear wife and I are sold. We purposely chose an RV with a residential type 110v fridge because it is handy for us. Of course somebody will immediately pipe up how terrible they are, but it really depends on preferences at this point. In different circumstances I might choose propane. I just hope what we have is durable in transit. So far... knock on wood. I had even considered, as you have, converting our old RV (a TT) to a small residential fridge some years ago, inspired by a clever thread written by another member on a different RV forum.

We personally like our straight electric partly because it is about as large a fridge as one can get factory-made in a Class C. It has 10+ ft of fridge and 4+ ft of freezers that add up to just short of 15 cu ft. Yet it's only 28 inches wide. It has narrow double fridge doors and two deep freeze drawers; it opens for easy access, even when the slide is in. When on the road, it runs automatically off a built-in 1000W inverter that is primarily powered by the chassis alternator, or directly by just the house batteries when the engine is shut off. It's efficient as heck. I usually no longer carry ice for an outdoor beverage cooler, just blue ice-packs that I exchange as often as I want because they freeze fast. Though once in a while, on a really hot day, I miss reaching into icy water for a cold one.

Then there are the off-beat things that happen. Even without the zombie apocalypse.

Recently we had to park in a remote primitive area on a very hot day because we chanced... and lost... trying to get a nice 110v hook-up at the last minute on a Thursday. The tucked-away camp-spot we got was quaint, but quite unlevel, front-to-back. The long wheelbase on Motor-coaches are hard to level since they can't just tilt on the middle axles, but need one end raised way up, way more jack and blocking than I had. So we 'leaned' back, camped tilted and ran the generator a while for late afternoon A/C, shutting it down plenty early before sundown.

On the inverter and batteries, our compressor fridge could easily run unlevel all night (it doesn't run much), plus I plugged a 110v CPAP into the same outlet. The two cheap house batteries were still in pretty good shape by morning. They charged back up from the engine alternator as we packed, dumped and left. We don't have solar yet. This situation wouldn't have been so good with propane. I'm not even sure propane would have cooled at all.

If any compressor fridge mounted in the old location appeals to you, you might also run across a similar unexpected advantage. It could be 12v or 110v, conversion kit, specific RV or dorm, depending on how you configure it.

Wes
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Old 08-28-2020, 06:56 AM   #4
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Quote:
Originally Posted by 2007 Sabre RnR View Post
We have a 12 year old Dometic Absorption Refrigerator, RM3762LB, in our 12 year old Sabre 5th wheel. It has gotten tired and is taking longer to cool down and has more trouble keeping cool on hot days.

We are considering replacing the refrigeration unit with a 12volt compressor style retrofit from JC Refrigeration. https://jc-refrigeration.com/product...-5a-90w-12v-f/

Does anyone have any comments on this type of conversion that they would be willing to share? We are still researching.

Thanks for your help.
The conversion is appealing and I am looking at it in the future when my RM3862 gives up the ghost. My fridge is about 8 cu. ft. However, the more I study it, the less I like. The one clear advantage is that I don't have to remove the old fridge from the coach. It won't fit through the door and neither will its replacement so out the dinette window it goes.

I thought that the price was appealing also. The conversion for my fridge is only about $700. However, my fridge is also 14 years old and the door seal needs replacing. That's another $300. It's still cheaper than a new fridge from Norcold, Dometic, NovaKool, etc., but it's still an old box.

I've replaced a 3-way dometic in a Class B with a 12v NovaKool and the performance difference was night and day. This was a 3 cu. ft. unit. I also installed a digital thermostat at the same time so I could set the temp I wanted (not 2 or 3 on the dial, but 35.5 degrees on the display) and the fridge maintained that temp. The installation also involved bringing the battery capacity up to >200Ah and 300 watts of solar on the roof. The Danfoss compressor draws about 2.5 Ah so potentially 60 Ah per day. That's a lot. If the conversion draws 7.5 Ah, that's gonna take a ton of battery to support. Class Bs tend to get driven everyday, too, so charging the batteries was easy.

I don't believe the 2.5 Ah claim on the Everchill unit on the etrailer site. Companies with far better reputations and track records like NovaKool, Isotherm, Vitofrigo and Engel come no where near that number. A NovaKool fridge in the 7 cu. ft. range uses 4-5 Ah while a 9 cu. ft. unit will draw over 5. The J.C. Refrigeration conversion does not use a variable speed Danfoss compressor but instead uses a no-name Chinese knock off that I can't find any info on. I believe their 7.5 Ah claim. At a 50% duty cycle, that's 90 Ah per day. You better have a lot of battery and a way to charge it quickly everyday unless you only visit sites with electricity. If that's all I did, I'd swap it out tomorrow. But I frequently boondock so I need to select something more efficient. I will never replace it with an absorption unit after living with an efficient compressor type.

Hope that helps.
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Old 08-29-2020, 11:44 PM   #5
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Quote:
Originally Posted by eric1514 View Post
The conversion is appealing and I am looking at it in the future when my RM3862 gives up the ghost. My fridge is about 8 cu. ft. However, the more I study it, the less I like. The one clear advantage is that I don't have to remove the old fridge from the coach. It won't fit through the door and neither will its replacement so out the dinette window it goes.

I thought that the price was appealing also. The conversion for my fridge is only about $700. However, my fridge is also 14 years old and the door seal needs replacing. That's another $300. It's still cheaper than a new fridge from Norcold, Dometic, NovaKool, etc., but it's still an old box.

I've replaced a 3-way dometic in a Class B with a 12v NovaKool and the performance difference was night and day. This was a 3 cu. ft. unit. I also installed a digital thermostat at the same time so I could set the temp I wanted (not 2 or 3 on the dial, but 35.5 degrees on the display) and the fridge maintained that temp. The installation also involved bringing the battery capacity up to >200Ah and 300 watts of solar on the roof. The Danfoss compressor draws about 2.5 Ah so potentially 60 Ah per day. That's a lot. If the conversion draws 7.5 Ah, that's gonna take a ton of battery to support. Class Bs tend to get driven everyday, too, so charging the batteries was easy.

I don't believe the 2.5 Ah claim on the Everchill unit on the etrailer site. Companies with far better reputations and track records like NovaKool, Isotherm, Vitofrigo and Engel come no where near that number. A NovaKool fridge in the 7 cu. ft. range uses 4-5 Ah while a 9 cu. ft. unit will draw over 5. The J.C. Refrigeration conversion does not use a variable speed Danfoss compressor but instead uses a no-name Chinese knock off that I can't find any info on. I believe their 7.5 Ah claim. At a 50% duty cycle, that's 90 Ah per day. You better have a lot of battery and a way to charge it quickly everyday unless you only visit sites with electricity. If that's all I did, I'd swap it out tomorrow. But I frequently boondock so I need to select something more efficient. I will never replace it with an absorption unit after living with an efficient compressor type.

Hope that helps.
Thanks for your post, Eric. Good info and some good thinking.

Although our Hisense compressor fridge seems to work great for us, I really should make an attempt to record it's actual power draw. I kind of wonder if the digital-display controlled compressor isn't a more modern efficiency design. It does have a super-cool/super freeze feature that allows it to later reduce power draw when it isn't needed. Off-hand I don't see how that can happen without compressor speed variation.

Perhaps our Hisense, and the Everchill, have a variation of the Danfoss Compressor, or a similar feature, since they can both supposedly vary their cooling rate. They've been around for a while and are for sale on ebay. Here are some info links to Danfoss:

https://en.wikipedia.org/wiki/Danfoss_Compressors_GmbH

https://youtu.be/jl5IWkGSfJY
(Tech Tip - Danfoss/Secop BD35 and BD50 Compressor Overview)

https://www.danfoss.com/en/products/compressors/dcs/compressors-for-refrigeration/mobile-dc-cooling-compressors/#tab-overview (also has a note concerning counterfeits )

It seems to me the trend to general RV compressor refrigerators is just really starting. Perhaps the handy small units showing up in outdoor kitchens is helping kick-start it. Like any change, there does seem to be a current learning curve with mid-size units (between dorm size & full size residential). There may be a falling-out of new upstart brands. Going by forum comments, either some units recently were not up to snuff (counterfeit?), or some RV manufacturer power plans are short-sighted.

Our Hisense RF 15N1BSD is working commendably, but I'm still having some difficulty finding our exact fridge on line, particularily in the U.S. But here is a Canadian link to a 15 cu ft Haier unit that appears the same:
https://www.canadianappliance.ca/HRF15N3AGS.html .

The Canadian company shows our model either discontinued by Hisense or discontinued in the appliance dealers own stock, with the still-available Haier probably a good interchangeable substitute in case of failure. The Haier linked above states it is assembled in the U.S. Most of the parts are almost surely manufactured in Asia somewhere, but I suppose at least the doors are installed by the dealer.

Since a 15 ft fridge is rather compact, I would think most customers would choose a slightly larger model for their brick-&-mortar home, probably at very little extra cost. That marginal sales market for 15 footers may account for them being hard to find. OTOH, at 200 pounds, and nearly 6 feet tall, they are also too large for a dorm... I would think.

I think Forest River includes these 15ft Hisense units in at least one other RV, a 5vr.

Wes
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Old 08-30-2020, 12:01 AM   #6
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The advantage of getting an entire new 12V compressor fridge is that you will have 10 cuft in the same footprint of your present 8 cuft.
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Old 08-30-2020, 12:03 AM   #7
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Originally Posted by eric1514 View Post
I don't believe the 2.5 Ah claim on the Everchill unit on the etrailer site.
And if you look even further on the etrailer site, they have other numbers. Never trust etrailer advice unless you double check.
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Old 08-30-2020, 06:43 AM   #8
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And if you look even further on the etrailer site, they have other numbers. Never trust etrailer advice unless you double check.
True. Just a few questions in we get a number of 11 Ah. That's seems high but more realistic.
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Old 08-30-2020, 07:31 AM   #9
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Do your research well.

Reading specifications by a beginner is confusing and misleading at best. Did that for a living in the past.

Remember when the Ford F-150 payload was listed from up to #4800? You needed to know the rest of the story!

Motor homes are quite different than trailers. Be careful whos testimonial you are listening to. Motor homes typically can charge batteries when traveling and have built in generators. Towed rvs do not.

Where you live matters. Where you camp matters.

Modern electric fridges are not made like your grandmothers old 40 year old GE in her basement.

Study hard!
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Old 08-30-2020, 08:24 AM   #10
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I applaud reefer manufacturers who are starting to quote AH ratings rather that instantaneous current draws. Inverter (or DC or BLDC) reefers use a 3 phase "DC" motor that is driven exclusively by a dedicated driver module. They result in variable speed (variable cooling) and virtually no startup surge. However, they generally do not operate like you grandfathers reefer. These units generally don't startup and run to temperature and then shutdown like old units do. They startup very slowly, run to temperature and then slow down and attempt to maintain temperature with very low RPMs. As such, they generally draw some level of current ALL THE TIME! My 22 cu/ft Frigidaire draws 50 amps of DC during about a 15 minute defrost cycle and then drops down to between 5 and 12 amps of DC for almost the next 7 hours, after which the cycle repeats. Now that is hard to describe to a buyer. Easier to integrate all this and simply say that it uses 8 AH. All of these power draws include inverter losses.

So 7.5 AH sounds reasonable, 2.5 sounds a little low. However, using this kind of specmanship a 7.5 AH reefer will use 180 AH per day. 4 deep cycle batteries will have around 200 AH useful capacity which means about 28 hours of run time before recharge without other loads.
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Old 08-30-2020, 09:03 AM   #11
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Are the Everchill 12 volt refrigerators, that are in a lot of new RVs use this variable speed cooling system? Or do they just cycle on and off? Jay
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Old 08-30-2020, 11:01 AM   #12
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Are the Everchill 12 volt refrigerators, that are in a lot of new RVs use this variable speed cooling system? Or do they just cycle on and off? Jay
From the attached schematic, the Everchill is an inverter driven BLDC compressor system. The 11 amp rating is clearly for the defrost heater which is 120 watts. I am sure the compressor draws much less. The actual cooling cycle is in question since the schematic doesn't show anything about the control circuitry.
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Old 04-03-2021, 07:06 AM   #13
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Quote:
Originally Posted by eric1514 View Post
The conversion is appealing and I am looking at it in the future when my RM3862 gives up the ghost. My fridge is about 8 cu. ft. However, the more I study it, the less I like. The one clear advantage is that I don't have to remove the old fridge from the coach. It won't fit through the door and neither will its replacement so out the dinette window it goes.

I thought that the price was appealing also. The conversion for my fridge is only about $700. However, my fridge is also 14 years old and the door seal needs replacing. That's another $300. It's still cheaper than a new fridge from Norcold, Dometic, NovaKool, etc., but it's still an old box.

I've replaced a 3-way dometic in a Class B with a 12v NovaKool and the performance difference was night and day. This was a 3 cu. ft. unit. I also installed a digital thermostat at the same time so I could set the temp I wanted (not 2 or 3 on the dial, but 35.5 degrees on the display) and the fridge maintained that temp. The installation also involved bringing the battery capacity up to >200Ah and 300 watts of solar on the roof. The Danfoss compressor draws about 2.5 Ah so potentially 60 Ah per day. That's a lot. If the conversion draws 7.5 Ah, that's gonna take a ton of battery to support. Class Bs tend to get driven everyday, too, so charging the batteries was easy.

I don't believe the 2.5 Ah claim on the Everchill unit on the etrailer site. Companies with far better reputations and track records like NovaKool, Isotherm, Vitofrigo and Engel come no where near that number. A NovaKool fridge in the 7 cu. ft. range uses 4-5 Ah while a 9 cu. ft. unit will draw over 5. The J.C. Refrigeration conversion does not use a variable speed Danfoss compressor but instead uses a no-name Chinese knock off that I can't find any info on. I believe their 7.5 Ah claim. At a 50% duty cycle, that's 90 Ah per day. You better have a lot of battery and a way to charge it quickly everyday unless you only visit sites with electricity. If that's all I did, I'd swap it out tomorrow. But I frequently boondock so I need to select something more efficient. I will never replace it with an absorption unit after living with an efficient compressor type.

Hope that helps.
I just revived this necro-thread to correct the record incase someone stumbles across. it

I had said that the JC Refrigeration conversion kit did not use a variable speed compressor and because of that, I was not inclined to do the conversion.

I was wrong. They do use a Danfoss/Secop type compressor in their units and I will be converting my fridge probably next winter. I've spent too much money this year on battery projects already. Time to do some camping.

Also, I found a high quality door seal kit on eBay for 1/2 the price of the OEM offering and I installed that a few weeks ago.
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