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Old 08-20-2004, 03:14 PM   #1
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Dometic refrigerator 12vDC operation

I have a 2003 Dometic RV refrigerator model RM2551 which is two way LP/120vAC. Is it possible to convert it to model RM2554 which is same basic unit except 3 way LP/120vAC and 12vDC so it can run while driving on vehicle 12vDC? It appears it requires the 12vDC heating element, wiring to circuit board and perhaps a switch. Anyone done this? Where can I obtain 12v heater element?

Thank you, Walter
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Old 08-20-2004, 03:45 PM   #2
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Should be possible

I have been thinking of the same thing. The difference is that on the boiler, there are two metal tubes instead of one. One tube for the AV heater and one tube for the DC heater. I would think a second tube of appropriate size coule be clamped tight to the boiler, the DC heating element inserted, and a heavy wite run to a heavy duty switch which would be wired to the battery with appropriate size wire. The switch could be anywhere and completely independent of the refrigerator controls; the DC element will never overcool the refrigerator. Thermal grease could be used to get good heat transfer.

Just make sure to turn it off when the unit is in operation. Also, you wouldn't have the low-voltage battery protection of the standard refrigerator controls.

You should find the wattage and part number for the DC heater in the manual (there is usually a single manual for the 2-ways and 3-ways with electrical diagrams for each). The Dometic site also should have the info. With the part number or wattage in hand, order the heater from Camping World or any RV supply.
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Old 08-21-2004, 11:39 AM   #3
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Walter, I have the 3-way Dometic, but I don't find the 12 volt system much use. If I remember correctly, the current draw is about 22 amps. It takes a high-grade wiring system to get that much current from a tow vehicle alternator and pass it through 30 feet of wiring and the 12 volt heater element in the refrigerator. My Dodge Ram 3/4 ton will not keep up with the demand. When travelling, some are happy to use the LP gas system (turn it off before entering a gas station), and others find that the contents stay frozen all day without any cooling. You can always pack a load of ice in the refrigerator, or turn it to its coldest for a few hours before travelling. In short, for my purposes the 12 volt system does not justify its complexity or expense. Nick.
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Old 08-21-2004, 12:01 PM   #4
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I found out by replaceing an altenator onmy tow vehicle a few years back that the 12 volt system is really not worth it.

I understand your concern of driving with the LP on, but that isn't as bad as you might think.

If you insist on traveling with cold stuff and don't want to use the LP then you might consider using an ice chest. Or you could just buy the stuff you need at a nearby store after you get your camp set up.
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Old 08-21-2004, 12:20 PM   #5
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Dometic refrigerator 12vDC operation

I have always had the Dometic 3-Way refrigerators in my Brand X coaches and have never had a problem operating on 12-volt - - and this is since my first coach that was equipped in this manner in 1980. I have never traveled with the refrigerator set to LP, and turning off the LP valves is on my checklist of pre-travel tasks. The dealer who wires my tow vehicle has always known in advance of the refrigerator system and has wired accordingly. On my older tow vehicles, I utilized heavy duty alternators with adjustable regulators - - but have made no particular modifications to either my '99 Suburban nor its '95 Chevrolet predecessor. In fact, since having the new Dometic 3-way refrigerator in my '64 Overlander (installed in 1999), the LP mode has only been used long enough to be sure that it functioned properly. A key hint in having the system function properly is to pre-cool the unit using the 120-volt element (or LP if you prefer), then switch to the 12-volt. There is no question in my mind that when the original Dometic 2-way refirgerator in my Minuet fails that it will be replaced with a new 3way Dometic.

Good luck with your investigation!

Kevin
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Old 08-21-2004, 07:30 PM   #6
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Thanks for the input. It still sounds like a good idea if it works well but I don't want to be buying alternators. I plan to do a lot of boondocking away from city power source. I’m just very unsure about towing on dirt forest roads and long highway stretches with LP flame going. That could be worse than no refer, no more trailer. I can use LP while camping and cool it down good before travel. I found the schematic for wiring but no part numbers. Wiring and switch are easy, I need heater element number and install info. Dometic offers only “You can’t legally do that”.

New Idea:
Can I run it on AC inverter power while driving and charge battery through tow vehicle?
Thank, Walter
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Old 08-25-2013, 12:03 PM   #7
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Dometic 12v operation off battery bank/solar while towing?

Our experience with our Dometic RM 3762 in our 2009 International is that it does not keep cool enough on propane in 90plus temperatures that we often encounter in the West. It does a much better job on AC--it cools down more quickly, and holds temperatures during the hot days better.

While traveling, running on propane on hot days is inadequate to keep contents at safe temperatures, and the reefer often turns off from wind blowing out the propane fueled flame, making the situation worse.

We have upgraded our Airstream provided solar system to 4 Lifeline AGM six volt batteries yielding a 440 amp battery bank for boon docking, and have 260 on the roof instead of the stock 112. We have the Airstream-installed 600 watt inverter, and there is already an outlet from the inverter in the reefer cabinet for access for another small-draw appliance.

(1) Will the 600 watt inverter safely handle the load from the Dometic RM 3762, both at startup and continuously if we plug the Dometic into the inverter outlet?
(2) Is there any way to isolate the load on our 2012 one-ton Sprinter's alternator so that the battery bank is still being charged by solar when towing?

Thanks!
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Old 08-25-2013, 12:27 PM   #8
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gecko: fans can make a dramatic difference.

There are three possible places to put them, up to you to decide which one might give you what you need.
  • Under the top cooling unit fins (back of refer) will dramatically increase cooling effect at fins.
  • at the opening to the roof vent will dramatically improve air circulation behind the refer (remove hot air from cabinet)
  • on the fins inside the refer. there are kits sold that make this a neat-looking and effective solution to extra cooling, simply by moving the air around inside the refer. Great if your family likes to "window shop" in your refer.

I would recommend installing switches so that any or all fans may be turned on or off. Those little "muffin" fans (commonly used in computers, can be bought cheaply at computer recyclers) do tend to be quiet, but it might be a Good Thing to be able to silence some or all at night...

The fans are low power consumers, BTW. All the ones I bought (four for $20) draw only 0.15A each.

Also, investigate the cavity behind your refer with an eye to increasing the flow over the top cooling unit fins. In some installations a big difference can be made by just using some home-made baffling.

I am about to try the "inside refer" fan plus the "in the roof vent" fans. If my family ever leaves me some time for doing this, I promise to report back.

Aage
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Old 08-25-2013, 12:43 PM   #9
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Can you provide any more info on the inside the refer kits for moving air around? I have used something similar on my boat but they were battery operated.
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Old 08-25-2013, 04:28 PM   #10
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Can you provide any more info on the inside the refer kits for moving air around? I have used something similar on my boat but they were battery operated.
Have a look here. He provides at least two different models, one marginally more expensive than the other, why I do not know.

The good part is that if your refer has an interior light, getting power is really simple (mine doesn't ) At the worst though, every fairly modern refer needs 12VDC for its "brains" (PC board), so power is rarely far away. The fan set itself merely pushes onto the fins of the cooler. Brilliant!
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Old 08-26-2013, 12:31 PM   #11
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12 volt dc thru inverter

Thanks for the fan/baffle tips.

Since you indicate that you are thinking about trying these, this has been our experience in the past with these suggestions:

Interior fan: We tried an excellent battery operated model at our dealer's suggestion. But the limiting factor was placement of stuff inside the refrigerator to allow circulation more than an actual fan to force circulate air. Once we rearranged stuff, the refrigerator was better able to handle the load, and the fan seemed to make little difference other than taking up more room. But at the start of a long trip, we do have a lot of stuff to fit into the reefer! The fan attached to the fins sounds VERY cool, though :-)

Chimney fan: This was another suggestion from our Airstream dealer. Because we're in SoCal, a lot of folks are taking their Airstreams into the desert where temperatures over 100 are common. Beautifully mounted with a very tasteful shut off switch (not only for quiet, but also to further reduce amp draw when dry camping), this device did--absolutely nothing to help!

Coil fan/Baffles: Haven't tried this one. But ironically, if one where to put air baffles on the air vents for this compartment (to keep the propane light from blowing out while towing), it would actually reduce air flow over the coils, too. Theoretically possible to build a separate baffle box around the flame area, and then a separate fan to blow on the coils.

But with the lack of success of the first two perfectly logical solutions above, I'd kinda like to cut to the chase and get this thing solved. In every case, no matter how the inside of the reefer is packed, running the reefer on AC has always yielded much faster initial cooldown, much lower ambient temperatures, and shouldn't blow out while going down the road.

So back to the original question--(a) will the Airstream installed 600 watt inverter that's already in our coach handle the initial and sustained load of our Dometic running in AC mode and (b) to avoid any alternator overload while towing, is there any safe way to keep the trailer lights/electric brakes hooked to the truck but still isolate the trailer battery bank/inverter system from the truck's alternator, leaving the battery bank to depend on solar only?

This combo would inexpensively allow us to run the reefer on AC while towing without damaging the Sprinter's alternator, with all the benefits to the reefer system. We typicallly plug in to shore AC in the evening while traveling, so the batteries would top off at night if the solar didn't keep up during the day.

Thanks everybody!
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Old 08-26-2013, 01:11 PM   #12
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I just ordered the Deluxe one that fits on the fins. I'll check back in when I've had a chance to install and test it.
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Old 08-26-2013, 05:06 PM   #13
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Quote:
Originally Posted by gecko View Post
Our experience with our Dometic RM 3762 in our 2009 International is that it does not keep cool enough on propane in 90plus temperatures that we often encounter in the West. It does a much better job on AC--it cools down more quickly, and holds temperatures during the hot days better.

While traveling, running on propane on hot days is inadequate to keep contents at safe temperatures, and the reefer often turns off from wind blowing out the propane fueled flame, making the situation worse.
Why not fix the propane system? You probably have a clogged orifice, a defective or misadjusted gas valve, or perhaps the tank regulator isn't providing propane at the proper pressure.

Quote:
We have upgraded our Airstream provided solar system to 4 Lifeline AGM six volt batteries yielding a 440 amp battery bank for boon docking, and have 260 on the roof instead of the stock 112. We have the Airstream-installed 600 watt inverter, and there is already an outlet from the inverter in the reefer cabinet for access for another small-draw appliance.

(1) Will the 600 watt inverter safely handle the load from the Dometic RM 3762, both at startup and continuously if we plug the Dometic into the inverter outlet?
Yep.

Quote:
(2) Is there any way to isolate the load on our 2012 one-ton Sprinter's alternator so that the battery bank is still being charged by solar when towing?
Not sure what you're trying to accomplish. Usually the path is high-resistance enough that the alternator won't do much anyway. If you don't want it to charge the batteries at all, just disconnect the charge line somewhere.
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Old 08-26-2013, 05:49 PM   #14
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Our experience with our Dometic RM 3762 in our 2009 International is that it does not keep cool enough on propane in 90plus temperatures that we often encounter in the West. It does a much better job on AC--it cools down more quickly, and holds temperatures during the hot days better.
Then you have a propane system problem. The propane puts more BTUs in the system than does the AC heating element. The box should cool more quickly and stay cool better on propane.

A post above mentions some things to check. In my case, it was the regulator set too low that caused poor cooling on propane. Once I had the proper propane pressure, the box cools great in even the hottest weather.
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