convert old RM360 to a 3-way with RM2130 parts

Update - it works perfectly in the backyard test.

I cooled the fridge down for 24 hours on LP. fridge temp was 37 and freeze was 0F this morning.

Shut the LP off and switched to 12v. 12 hours later the fridge and freezer have both gained about 3 degrees.

MrWizard wrote:
unless the fridge has ventilation with the pup closed
you can not run on battery either
this mode also creates heat in the boiler to move the amonia mixture
and do the cooling

Of course it does but not much. With the fridge on LP on a very hot day, the hottest spot on the coils was around 190F I'm thinking that little probe will get warm but not close to being able to ignite anything.

And I will come up with some sort of ventilation. Just not sure I'd be comfortable with an open flame inside the folded popup.

unless the fridge has ventilation with the pup closed
you can not run on battery either
this mode also creates heat in the boiler to move the amonia mixture
and do the cooling

hertfordnc wrote:
This is a popup that did not come with a fridge. I have not completely worked out the ventilation yet but I would not run the fridge on LP with the popup down and in tow.

The 12v element draws ten amps so running it off the 7=pin should not be a problem.

I think the reason 3-ways are out of vogue is the same reason new RVs come with televisions on the outside- because it's no longer about camping. And I'm sure they had trouble educationg people on the limitations.

Of course it won't cool properly on 12v. That's about 300 btus and it needs three times that to work properly.

But, if i take off with it cold and loaded I'm pretty sure the 12V element will minimize the loss over 10 hours of driving.

"The 12v element draws ten amps so running it off the 7=pin should not be a problem."

The 7-pin will start out at say 15 amps but will quickly taper to more like 5 amps within say 15 minutes (you can measure that happneing with your ammeter) due to the way alternators work.

So expect a 5 amp "loss" going down the road. (Which can be made up if you have solar and the sun is out) Depends on how long you drive (10 hrs = 50 AH down) and the battery situation at the start what happens. Then you have to consider if that night you have a chance to recharge the batts.

All very situational. Could work.

BTW if the multimeter only does 10 amps as an ammeter, it should be the kind you can replace the fuse if the amps are too high. A Trimetric is safe to use for this measurement.

This is a popup that did not come with a fridge. I have not completely worked out the ventilation yet but I would not run the fridge on LP with the popup down and in tow.

The 12v element draws ten amps so running it off the 7=pin should not be a problem.

I think the reason 3-ways are out of vogue is the same reason new RVs come with televisions on the outside- because it's no longer about camping. And I'm sure they had trouble educationg people on the limitations.

Of course it won't cool properly on 12v. That's about 300 btus and it needs three times that to work properly.

But, if i take off with it cold and loaded I'm pretty sure the 12V element will minimize the loss over 10 hours of driving.

If it is decided not to run the fridge on propane going down the road (except at gas stations and on ferries of course) then you can run the fridge:

A. On 120v via inverter at some DC battery draw for that, or

B. Run the fridge on its 12v element at some battery draw for that.

Do we have any comparable DC battery draws data for those two ways that would help decide which might be better?

3 Comments
1: The absorption unit IS identical so you can do as you plan
2: I would not do it however
3: The reason... The A/C element is in the range of 300-400 watts.
So what does that mean: Well sometimes the DC element is de-rated (Say 200-250 watts in fact I think that's it) which means it won't cool as well. in hot weather it may not cool well enough. Also that's a 20 amp load, If it is in a trailer the charge wire from the Engine on the tow vehicle is not going to pass that much current. and on a Motor home you likely won't make it either. So it is a very short term solution at best.


There is a reason that 3-way units are hard to find now days.. and that is it. The 12 volt option just did not work well.

NOW what does work? Both dometic and Norcold had, at one time, a high effiency compressor job.. I have a small chest freezer that uses the same technology.

Instead of 300-400 watts. it sucks a great whopping 30-40 watts.. Yup 1/10 the power of the AC element. NOTE these are all electric fridges.

My freezer is 12 years old sometime this summer.

I occasionally defrost,, Blew dust out once. that's all folks.

Thanks for the update. Good info.

Hey, thanks everyone but ya'll were pretty much useless. I must be getting old.

It looks like Dometic saw me coming. EVERYTHING on both fridges is completely interchangeable.

On the pipe that carries the heat to the absorption unit there are tubes welded on for the AC and DC heating element.

The electrical selector is also identical. All i had to do was install the 12V element, add the wires, and change the selector knob.

No idea if it is proper procedure, but I saw somewhere while reading up on these fridges, that you can sort of reset the ammonia by laying the fridge on its side. Perhaps Doug can advise on that.

I found the instructions for my 7401L on line; perhaps there is trouble shooting info there for your fridge too.

The other way to to run the fridge while driving is use an inverter to operate it on AC. That is if as it appears you don't want to leave it running on propane ( except when at a gas station or on a ferry of course)

Mr Wizard is right about the Dometic 7401L at least---the instructions say the 12v element wires must be so the 12v can only operate when the vehicle's ignition is on. The electronics 12v has its own set of wires to be permanently connected to the rig's 12v (with a 2a fuse)