Why a 3-Way vs a 2-Way Fridge?

Why would one want a 3-way fridge as compared to a 2-way?  The new compressor technology draws very little amperage on DC power.  It would seem to me that a 2-way would be much preferable to the critical operating conditions - mostly the need for the unit to be level - needed for a 3-way's propane operation.  It would also save propane for other needed operations like hot water, cooking, heating and the generator.

I'm getting ready to order a new Sprinter based Class B;  and am planning  to ask the conversion company to provide a 2-way fridge in place of their standard 3-way.

Am I missing something?

As a reference point, I have an Engel chest type fridge that will run for several days with the car parked without depleting my car battery to the point where it won't start the car.

From what I have seen, 3-way fridges usually have a small form factor.  Once you get up to a certain size, they are 2 way.  I'm not sure size is the only reason, but at least that is what I observed.


One of advantage of the 3-way is the ability to run the fridge on 12V while driving.

Please define what you mean by "2-way".  It sounds like you want an all-electric refrigerator that will run on either 120VAC or 12VDC,  but no propane.  To my knowledge, a standard RV "2-way" fridge has 120VAC and propane as options, but no 12VDC.

Am I correct as far as what you are looking for?

bigbit said:

Please define what you mean by "2-way".  It sounds like you want an all-electric refrigerator that will run on either 120VAC or 12VDC,  but no propane.  To my knowledge, a standard RV "2-way" fridge has 120VAC and propane as options, but no 12VDC.

Am I correct as far as what you are looking for?

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That appears to be the case with Dometic.  Norcold's sells an AC/DC; and that is what I want.  My "2-way" terminology is obviously wrong.

Here's an example of what I mean:

http://www.thetford.com/HOME/Products/NorcoldRefrigeratorsHome/DE0061EV0061/tabid/197/Default.aspx

To quote from the Norcold AC/DC Fridge web page:

Reliability On the Move

Quiet, dependable and designed for years of service, our AC/DC refrigerators are ideal for marine use as well as RVs, vans and trucks.

    * Exceptionally quiet even in close quarters
    * Easy, accessible storage with adjustable, removable door bins
    * Convenient, large container storage
    * Durable, easy-to-clean white powder-coated shelves
    * Safe and stylish recessed doors
    * Off-level operation up to 30?

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Don't confuse the RV style refrigerator with residential type compressor units.  3 way means propane, 120VAC and 12VDC, while 2 way is just propane and 120VAC.  Both are absorption type cooling units.  Compressor models are 120VAC only and use no propane, thus are a 1 way refrigerator.  A residential refrigerator can be run on 12VDC by use of an inverter to generate the 120VAC.

That Norcold AC/DC model is a fairly new development and I don't know of any RVs that offer it yet.  It is a good consideration as a replacement for a failed absorption refrigerator if you can't find a residential model to fit in the space available.

Ned said:

Don't confuse the RV style refrigerator with residential type compressor units.  3 way means propane, 120VAC and 12VDC, while 2 way is just propane and 120VAC.  Both are absorption type cooling units.  Compressor models are 120VAC only and use no propane, thus are a 1 way refrigerator.  A residential refrigerator can be run on 12VDC by use of an inverter to generate the 120VAC.

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Not the case.  See my link in the message above.

See my message above.

Ned said:

See my message above.

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As posted above, Norcold makes AC/DV fridges for RV use.  My terminology of "2-way" was obviously in error, but RV fridges that operate on 120VAC and 12VDC at off angles up to 30? are definitely available, and do not require a separate inverter.

Now, to my original question,  Why would one want a 3-way when a very efficient no-propane AC/DC fridge is available?

Ned said:

That Norcold AC/DC model is a fairly new development and I don't know of any RVs that offer it yet. 

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So far, one RV conversion company (and I've only asked one at this point) has said they would supply it in place of the standard Norcold N6x1 unit they currently use.

120V/12V units have been available in the marine industry for at least 20 years.  That is just how long I remember them.  Both Norcold and Dometic make them and they are available in sizes from tiny to almost residential sizes.  For the last 10 years at the plant I am presently at all we have installed is 120/12 units. 
A 120/12 unit will draw more current than an absorption unit when running on 12V power so may not be the best for boondocking.  But if you are in situations where you are always plugged in to shore or generator or on the road they would be an excellent choice.

DUTCH VanAtlanta said:

Now, to my original question,  Why would one want a 3-way when a very efficient no-propane AC/DC fridge is available?

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If you NEVER need to run the fridge without electricity (i.e. always on the road or plugged in), then you could do without propane. Propane's biggest advantage is that you can run with it for quite a while when boondocking, that is, no hookups. The 12 VDC operation requires batteries to operate (unless you can run a generator constantly), and batteries run down pretty quickly like that. A secondary consideration is resale of the RV -- I suspect few folks want an RV where you ALWAYS have to be plugged in or running your engine.

Propane refrigerators still require 12v to operate the control circuits.  They just do not draw as much as a 12V compressor.  A lot has to do with how many times you open the door and the ambient temperature.

Just a side note, but might be a consideration - we run our fridge on propane all the time, because it's just so efficient to do so.  The propane draw is very very low.  We ran it in excess of 40 days this summer on about 8 gallons of propane.

We had a 3 way Dometic fridge in our truck camper.  Unless things have changed since we had ours, the 12 volt mode did NOT cool very well and would run the battery down very quickly.    The propane selection uses very little propane, is more efficient and much better at cooling.  As mentioned you will have to be plugged in or running your engine to provide continual cooling.  You might find that a big draw back. 

You could just buy the 3 way and not use the propane mode.  That way at least you would have the option if you find the 2 way doesn't work as well as you like; or that you find you do camp without electricity.

Marsha~

OK, back to your original question.  Take a look at that ad you had in the link.  The current draw for 12 volts is 3.2 amps - that is rather a lot to be running off of a battery!  The reason dual 120VAC and propane units are so popular is that the propane heats the boiler (instead of a high-draw 120VAC heater), and 12VDC is used for the control power.  If you have a solar panel charging the battery, you can run this arrangement for weeks.  It would take a battery of solar panels, and some big batteries, to be able to do this with a dual 120 VAC/ 12VDC unit.

Unit your made this post, I had no idea these units were available.  Does anyone know if the compressor is a dual motor unit, or is an inverter built in?

more on the 3.2 amp draw.
lets say you are on a 2 week stay in a nice state park = no power and no generators.
so 3.2 amp over 2 weeks (336 hours) would need 1075 amp hours
to be on the safe side of your battery usage you only want to use 50 of the battery capacity. so you need a bank of batteries that will hold 2150 amp hours.
a trojan T-105 claims 250 Ah so you would need 8 of them! I don't know what one costs and I don't know of many RV's that would have space for 8 of them. and the above calculation does not include any other power usage......that is the reason I run on Propane.

As others have pointed out, the main consideration is the size of the batteries and how long you expect to remain in one place without recharging them.

If you'll only be dry camping a day or two at a time, you can get by with an electric refrigerator running from two house batteries.

If you expect to stay without hookups for longer periods, you'll need to think about charging the batteries while you're parked. Either from solar panels, running a small generator or (worst case) running the Sprinter's engine while you're parked.

You'll eventually have recharge the batteries regardless of what kind of refrigerator you have - the point is using an electric refrigerator will increase the current drawn from the batteries, so you'll have to recharge them sooner compared with just using the batteries for a couple of hours light each night.

As far as relative efficiency goes, when looking at the total energy used, a compressor refrigerator is MUCH more efficient than an absorption refrigerator.  The absorption unit uses 10-20 times as much power as a compressor refrigerator to deliver the same amount of cooling.  The difference is where the power comes from.  A compressor fridge draws all it's power from the batteries, the absorption refrigerator gets most of it's power from the propane tank, which holds much more energy than a battery.

Our first trailer was a Trailmanor, which is hard sided and folds down when taveling. When on the road it would run on 12v as the propane exhaust for the fridge was covered by the top. When parked you could run it on propane, 120v, or 12v. But it worked the best on 120v when parked.

Lou Schneider said:

As far as relative efficiency goes, when looking at the total energy used, a compressor refrigerator is MUCH more efficient than an absorption refrigerator.  The absorption unit uses 10-20 times as much power as a compressor refrigerator to deliver the same amount of cooling.  The difference is where the power comes from.  A compressor fridge draws all it's power from the batteries, the absorption refrigerator gets most of it's power from the propane tank, which holds much more energy than a battery.

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Thanks for this info and all the other comments in this thread.  Gave me lots to consider, but I'm still leaning towards the AC/DC fridge for the following reasons:

1.) A well designed and insulated fridge should not be running 24/7.  My Engel pulls 2.5 Amps on 12 VDC and cycles quite frequently, but it will easily go 2-3 days without discharging the battery enough to give problems starting the car; and this is in a hot desert climate.  I am not one to stay put for more than a day or two, so there should be ample recharge of the batteries from the engine.
2.) My home where the RV will be parked and loaded for a trip does not have a single area with less than 3? slope, so leveling for proper operation of the propane fridge will be impossible.  The AC/DC will operate just fine at up to 30? off level.  This is the main reason I'm looking towards the AC/DC fridge.
3.) Somehow, the idea of the much higher efficiency of a compressor fridge with an essentially free energy source (the engine, since an alternator always puts out way more than is required to power  the vehicle) vs a flame boiler fridge requiring propane fillups is very appealing to the admittedly very small "green" side of me.  After all, that one of the main reasons (fuel efficiency) I'm only considering Sprinter models in my RV research.  Hydrocarbon fuels ain't gonna get any cheaper.

Again, thanks for all the feedback!  Happy Trails to y'all!

To answer Natetheskate, the ones I know about use a DC compressor with a converter for the AC power.  Dometics Waeco brand is 120/240VAC-12/24VDC.  I loved them because we didn't worry if the boat was domestic or overseas.