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Old 07-11-2020, 03:47 PM   #1
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Fridge cooling unit swap to compressor unit

I've seen another thread or two on this topic so will try to add some points that may help folks decide to do this swap themselves (or not). TL;DR - the Dometic NDR1492 fridge is heavy and the job is tedious, but definitely doable. Need 2 strong people and lifting straps (or 3+ people) when lifting the fridge. The JC Refrigeration unit is decent quality but fitment can be finicky - test fit before foaming in, for sure! Also, take the opportunity with the fridge out to clean up, make any repairs/changes, insulate better, etc.

The PO of our 2000 class A had an updated ammonia/absorption cooling unit from JC Refrigeration installed on the Dometic NDR1492 by JC in 2016. It worked great until recently, warming up in some hot weather, after which we started to smell the distinct odor of ammonia out the fridge roof vent. We knew that meant impending failure of the cooling unit. We decided to go with a DC/12v compressor unit from JC Refrigeration instead of another ammonia/absorption unit. JC was surprised our little over 4 year old cooling unit was failing (as were we) & although the PO didn't purchase an extended warranty, JC still gave us a deep, deep discount on the new 12v compressor cooling unit. Great customer service!

The DC compressor swap in the back & keeping the 1492 box was the easy choice for us (instead of a residential fridge, such as the Samsung RF18) because we:
  • wanted to keep the original wood doors look of our 1492
  • found the 14 cu ft was plenty space for our needs
  • didn't want to lose the drawers underneath
  • didn't want to wrestle the 1492 out of the rig & another fridge in (via a removed window)
  • have 1140w of solar & 700ah of house batteries
  • primarily boondock/dry camp
  • didn't want to replace our otherwise functioning inverter to run an AC/120v fridge
We wanted to do a DIY install because we do nearly all work on our rig & we're nowhere near Shipshewana, IN (where JC Refrigeration is). We prefer our attention to detail over that of typical technicians, & my husband is a mechanic.

In covid-19 time, it took a good 7 business days for the unit to ship from IN to CA, via FedEx Freight Economy, and communication is not FedExs strong suit. It's shipped on a pallet laying horizontal & was packed pretty securely & well by JC. It weighs around 95 lbs on the pallet but significantly less once you unpack it. The compressor system is far simpler - and IMO better, as a result - than an absorption unit, even better than JCs own absorption unit (which is definitely better than the original Dometic absorption unit). There is so much less complexity, and heat, in the compressor system.

There are install videos by both JC & Mortons on the Move that are helpful. Some things not covered in those videos, though, are worth noting. First, the NDR 1492 is unwieldy and very heavy - it may well be the largest RV absorption fridge out there. We're 2 fit & strong individuals in our mid-40s & it was manageable for the 2 of us. The "forearm forklift" lifting straps were crucial. We shimmied it out of the cabinet and onto a sturdy storage bin, which saved us from having to get it out and all the way down to the floor, without damaging the wood surround. We then used the forearm forklift straps to set it upright on the floor. We positioned towels & cardboard on the floor, then lifted & turned it, in order to rock it forward onto its face. Towels are important underneath because even if you let it defrost & dry out for a couple days, a bit of water will still leak out when you move it around & rock it forward.

Once on its face, the old cooling unit comes off the back, then it's very much worth setting the fridge back upright to test fit the new cooling unit in. Ours took some manipulation to get it in so we were very glad we did a test fit (actually, several). It's also a good opportunity to correct any leaks & clean up the back, cabinet, etc (and in our case, add insulation to the fridge cabinet). We also decided to remove the ice maker since we never drink water from the fresh water tank - yay for more freezer space & less cords & electrical in the back!

The foam spray is pretty easy to work with but very hard to get off anything you dont want it on. We put old sheets over the dinette & couch, towels on the floor. We got a little spot of it on the Ozite material on the ceiling, but it is dissolved by alcohol before it cures, so it came right off. If you get it on your skin, you just have to let it come off on its own over the next several days (trying to pick it off will result in your skin going with it, ask me how I know!).

Once the unit was set in the foam, screwed on, and the electrical hooked up, we turned the fridge on while it was still out of the cabinet to make sure it was working well before putting it back in the cabinet. It started then stopped, then started again and ran nicely, taking a few hours but getting down to 36 in the fridge and 2 in the freezer - perfect. While running constantly, we did notice that the cold lines on the back coming from the compressor iced up and dripped a little bit of water, which we addressed in a couple ways. We replaced the insulation from JC on the cold line with better insulation and secured it better. We also decided to spray down a layer of clear rubber sealant over the wood along the rear 8 of the fridge cabinet where the drips would land, should it still drip. We also repaired a leaking drain line, hoping its all dry everywhere now!

Getting the fridge back in wasn't as difficult as we thought, with the aforementioned lifting straps. Hubby replaced the weatherstripping along the edges of the fridge because we were able to feel wind through the edges of the fridge, before the cooling unit swap. The noise from the compressor is detectable but not too significant. Its more loud than absorption, of course, but not annoying.

I'll discuss how it's working in a subsequent post.
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Old 07-11-2020, 04:15 PM   #2
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So, to the real-world performance of the 12v/DC compressor unit swap on our big ol' NDR 1492. Initially, it cooled right down to the degrees we wanted, 36 or so in the fridge and 2-9 in the freezer. Ambient temps were nothing crazy, 70s-80s. Once we left where we were parked & filled the fridge/freezer back up with food, it performed pretty well, getting up to 44-45 in some hot weather.

About 8 or so days in, we started seeing some troubling temperature margins between the fridge and the freezer, on the order of 36 or 37 and 19 or 20. We spoke to the folks at JC Refrigeration and they said they'd seen issues like that on the big 1492's, and to try a Snip the Tip thermistor. We happened to have one on hand that we purchased a while prior, and installed it. Whether it was an installation error, a faulty control board, a faulty thermistor (it was reading appropriate ohms so we didn't think so), or something else, we had an issue: the fridge would no longer switch the cooling off. It was not the most fun I've ever had, getting up multiple times in the middle of the night to either turn the fridge on or off, for several nights! We didn't want to just leave it running, since when we did, it got down to below 30 in the fridge and -15 in the freezer. We also didn't want to leave it off with a fridge and freezer full of food. We were in the middle of a visit to Crater Lake with friends so we just turned it on & off manually for those 5-6 days until we got to another location where we could fix it appropriately.

We contacted Dinosaur Boards and they let us know their control board for our fridge would not work with the 12v/DC compressor. Glad they told us before we ordered it!

Long story a bit shorter, we ended up going with an inexpensive 12v temperature controller unit from Amazon. It has a lot of options for cutoff temperatures, delays, etc and it has worked great. We still are playing with it and are glad it was a cheap and easy but massive difference maker for us. It's mounted in back, near the compressor (see photo).

We're now really happy with the compressor conversion! Hot weather performance can likely be perfected by adding a potentiometer, see Mortons on the Move's video. All in all, though, it's been a great unit and hopefully we can help others avoid some frustration if they, too, have some issues with the old electronics of an older fridge not playing well with the newer electronics on the DC compressor.

I wanted to add some info about the fans that come with the JC compressor unit. We already had a 3 fan setup from RV Cooling Unit Warehouse that worked great to keep the fins from icing up. We tried the 2 fan one that came with the JC compressor and they were quite a bit noisier and seemed to move less air, so we switched back to the 3 fans from RV Cooling Unit Warehouse and they have continued to do a great job of keeping the fins free of ice.
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Old 07-13-2020, 06:08 AM   #3
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I just drove to their shop last week to pick up my 12v unit. Started the conversion, but doing other needed work while doing the swap. Good to hear it’s working!
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Old 07-13-2020, 03:49 PM   #4
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Right now we're using one of the absorption cooling units from JC Refrigeration that we bought before he came out with the compressor-type. If it ever goes bad I will be replacing it with the compressor-type unit! Jr. gives fantastic service!
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Old 07-13-2020, 08:49 PM   #5
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Quote:
Originally Posted by srogers View Post
So, to the real-world performance of the 12v/DC compressor unit swap on our big ol' NDR 1492.
You seem to be pretty thorough. Is there a chance you have a Kill-a-Watt or some other way to measure how much electricity your compressor unit uses in a 24-hour period (preferably a few 24-hour periods)?

I've always been curious about how it compares to a residential refrigerator. All I can find is that it draws less than 1 amp, but never any indication about the duty cycle. On the one hand, a Norcold or Dometic box is generally smaller than the residential units people get (which could mean less electricity used in 24 hours), but on the other, I wouldn't be surprised the Norcold/Dometic box isn't as well insulated (which could mean more electricity used in 24 hours).

I suspect these Norcold/Dometic compressor units use about the same amount of electricity over 24 hours as a residential unit, but can't find any numbers on it anywhere.
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Old 07-14-2020, 06:29 AM   #6
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Quote:
Originally Posted by oatmeal View Post
You seem to be pretty thorough. Is there a chance you have a Kill-a-Watt or some other way to measure how much electricity your compressor unit uses in a 24-hour period (preferably a few 24-hour periods)?

I've always been curious about how it compares to a residential refrigerator. All I can find is that it draws less than 1 amp, but never any indication about the duty cycle. On the one hand, a Norcold or Dometic box is generally smaller than the residential units people get (which could mean less electricity used in 24 hours), but on the other, I wouldn't be surprised the Norcold/Dometic box isn't as well insulated (which could mean more electricity used in 24 hours).

I suspect these Norcold/Dometic compressor units use about the same amount of electricity over 24 hours as a residential unit, but can't find any numbers on it anywhere.
Believe I read on JC site @ 80*, the 12v runs about 64% duty, AC version runs at approx 55%, and estimated 350% more efficient than residential.
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Old 07-15-2020, 10:35 AM   #7
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Quote:
Originally Posted by oatmeal View Post
You seem to be pretty thorough. Is there a chance you have a Kill-a-Watt or some other way to measure how much electricity your compressor unit uses in a 24-hour period (preferably a few 24-hour periods)?
We haven't done testing to yield detailed electricity use. We've seen the unit use approximately 8 to 10 amps (DC) when running. How long it runs in a 24 hour period varies daily, based on ambient temps and how much the fridge has been opened.

Our 1140w of solar and 700ah battery bank have been easily able to account for the new draw it represents on our system, still reaching float status by 9 or 10am with summer sun & good exposure.

While propane fridges work well, we're pleased to eliminate propane running the fridge & thereby reduce the heat, need for propane fills, and potential fire risks (however small with precautions). DC compressor driven cooling was a no-brainer for us!
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Old 07-15-2020, 02:39 PM   #8
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I have a 2000 Country Coach Magna and i am considering the JC Refrigeration 12v compressored upgrade to my Dometic 1492. It just died. I’m evaluating having it done at a local RV service vs doing it myself. One company advised there was not enough room between The back of the Dometic and the outside wall of the RV. Looks like your fit just fine. What RV do you have?
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Old 07-15-2020, 08:19 PM   #9
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Originally Posted by US1 View Post
Believe I read on JC site @ 80*, the 12v runs about 64% duty, AC version runs at approx 55%, and estimated 350% more efficient than residential.
Thanks for posting that. I've looked all over that site more than once and never found it. It's in the "product information" section."

But man, is it confusing:

Quote:
again unlike a residential fridge that draws between 6-8A 960W AC, my unit draws only .8 A 92W which is less then what most inverters draw by themselves, so the power savings are a huge 350% less then what you had and up to 650% less the a normal residential fridge
Residential refrigerators (like the Samsungs) use about 1.5 kwh/day. If they really drew 960 watts, that would mean a 6.5% duty cycle. That's crazy.

And I don't know about other gas/electric refrigerators, but my four-door Norcold 1200 has two 225-watt heaters, so it draws 450 watts. It uses about 7 or 8 kwh/day--vastly more than a residential refrigerator.

So what they're saying about their compressor unit using 350% less than "what you had" (gas/electric?) and 650% less than "a normal residential fridge" is the exact opposite--the savings are much greater over the gas/electric than the residential. And the gas/electric uses 5 times the amount of electricity that a residential uses, so the 350% and 650% numbers don't make sense.

As for the duty cycle, they say:

Quote:
in our testing @ 80F the AC compressor will run approx. 56% and the DC approx. 64%, that is not opening and closing the doors.
This is interesting because if you take the 92 watts the compressor uses and multiply it by the 56% duty cycle, you get 1.24 kwh/day. And that's without opening and closing the doors. So it's right up there with the 1.5 kwh/day a residential refrigerator uses.

Which is kind of what I suspected, as I outlined above. But I've never been able to get numbers to actually calculate it before.

The reason I'm interested in this is that people may think that these units will use less electricity than a big residential refrigerator, and let that factor into their decision. And it certainly doesn't help that the website is claiming that the compressor unit uses 650% less electricity than a "normal residential fridge." Or, well, it might at a given moment, which would matter for sizing an inverter. But when measuring electricity use for pulling out of batteries or for an electric bill, it's kilowatt (or amp) HOURS that get measured.

It appears that the compressor retrofit and a new residential refrigerator will actually use about the same in a 24-hour period.
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Old 07-15-2020, 08:58 PM   #10
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I’m thinking of doing this swap. The PO of my mh had replaced the original fridge with a very small Norcold gas/electric and we need more fridge and freezer space. I picked up a Dometic gas/electric that supposedly everything works (boards, light, etc.) but doesn’t cool for $25. There was an ammonia leak from it. I’m going to do the best I can to test as much as I can and if everything seems to work (except for cooling) I want to put the 12v compressor cooling unit in it. I will use your post, along with other info to do my install.
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Old 07-15-2020, 09:36 PM   #11
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So how much room is needed between the back of the fridge and the outside access grill or wall?
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Old 07-16-2020, 07:45 AM   #12
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Installed the JC 120v last year in my 1200 norcold. I live just south of Atlanta, and very good Tech lives on the west side. He removed the frige using a elevating dolly sold by Harbor Freight, by himself. I helped lay the new cooling unit on the mastic. All other work was done by him. Took 3 hours which included dealing with board problems. My unit is 1999 vintage and required replacing the board and eyebrow panel. Three hundred dollars labor. For the problem of rear space, I made 3/4 inch spacers of oak, looks good. JR is very helpful with problems.
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