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Old 04-05-2021, 04:12 AM   #1
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With a 3 Way Fridge when to use 12V?

We are newbies awaiting delivery of our 1st RV (Class C). I have seen discussions in a number of forums on the safety of using propane while driving to operate the fridge. If you have safety concerns keeping the propane on while traveling, and assuming the batteries have the capacity to power the fridge, couldn't you keep the fridge operating and cooling by running it on 12V? Are the coach batteries being charged while the vehicle is operating as the chassis batteries do? Thanks in advance for helpful feedback.
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Old 04-05-2021, 05:39 AM   #2
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IF your fridge is propane it is not 12 volt. 12 volts controls your control board when on propane but does not cool your fridge. an absorption fridge must heat to cool and this is done two ways. by propane or house current.when plugged in
you can get a 12 volt compresser fridge but must have battery capacity to keep it running.
would add that 3 way fridges are 12 volt but use battery capacity quickly.
if your vehicle can recharge your batteries fast enough is something you'll have to find out.
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Old 04-05-2021, 06:11 AM   #3
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We had a class C with a 3-way fridge and it did cool with either propane, 12 volt or 120 volt. I found the 12 volt did not keep the fridge very cold so we really never used it on 12 volt. That was many years ago. I would think the new units work better. I would pre-cool the fridge before my trip on propane or 120 volt and check the temperature. I would switch to 12 volt while driving only and check the temperature when I stopped for the day. The alternator should be more than sufficient to keep the batteries charged while driving but on 12 volt they will run down quickly when stopped if you don't change over to propane or 120 volt if you are on ground power.

We now have a 2-way fridge that runs on propane when driving that works well. In 100,000 miles of driving we have never had a problem running it on propane all day. It draws the battery down very little in the propane mode because it is using the 12 volt only to power the control board.
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Old 04-05-2021, 06:36 AM   #4
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12VDC (3 way fridges) are few and far between these days. Most are 120VAC or propane. The 12VDC is absolutely inefficient in that the heating element can't generate enough Btus to easily move the coolant. Then there is the lack of battery capacity to operate these fridges more then a few hours before they are completely run down. I have owned 2 RVs with 3 ways and learned my lessons fast - propane or 120VAC, forget the 12VDC. I'm not sure that a gas 'C' has enough alternator capacity to keep the batterie(s) charged plus meet the rest of the coaches needs, including running the vehicle itself
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Old 04-05-2021, 11:44 AM   #5
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I use simple logic, leave on auto if I知 plug in I知 on ac power if genny is running I知 on that if I知 not on neither I知 on propane.
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Old 04-05-2021, 01:38 PM   #6
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3-way fridge...120VAC element, Propane and 12VDC element

The 12VDC is to be used when fridge is ALREADY cold
*Not for initial cooling down
Travel Mode is what it is intended for ----maintain a COLD fridge while traveling place to place


It's as simple as that..............
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Old 04-05-2021, 07:16 PM   #7
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We. are getting a 2021 LTV Unity. Based on the responses the 12v is pretty useless. I wonder why LTV provides the 3 way fridge and not just the 2 way. Thanks to all for your feedback
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Old 04-05-2021, 07:28 PM   #8
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I have only had 2 way in our 3 MHs.
I have had 12V / 120V fridges on 3 boats and never had any problems.
Current boat we cruised for 2+ mos and a mix of marinas with power and anchorages & lock walls w/o power. Frequently w/o power for 2-3 days & notes. Never a problem with over night on 12V we then ran gen for an hour for coffee, bfast and charging if we weren't getting ready to move on and charge via alt.
Again fine all day and might run gen an hour again in PM for coffee, dinner, etc.
All you need to do is calculate AH load and match to batty for the time you expect to run on 12V.
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Old 04-05-2021, 07:46 PM   #9
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Leave the propane on while traveling
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Old 04-05-2021, 07:56 PM   #10
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We has a couple 3w fridges in our campers. I call norcold one time about the 120v heater element.

In the conversation I discovered that the 12v heater had no thermostat control, with the reason that it was only cooling with 1/2 the cooling capability of the 120v heater. I check it out sure enough the 120v heater is about 2x the 12v heater. Found this to be true on other manufactures 3w fridges.

Our current fridge I set to auto. It runs on 120v, but when I unplug from shore power it switch to propane. When back on shore power it switch back to 120v. The only thing that does not work on propane is the ice maker.
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Old 07-20-2021, 08:02 PM   #11
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3 way, good use

We have a 2020 Unity with 3 way fridge.
You cool it down on 120v before leaving.
You can choose AUTO and the fridge will decide for you. Mostly it will switch on 12v while driving if you have a DC to DC charger, then switch to propane when stopped and not connected to 120v.
We prefer to use propane while driving it is more efficient and your alternator and DC to DC charger get a break.
We had a propane failure last week during a 5 day trip.(tank switch, major problem that could not be repaired quickly). We stopped at campgrounds for the nights and 120v.
Luckily, we had 12v. for the 15 hour trip back over 3 days. Otherwise we would have lost all content in fridge and full freezer.
Not a bad thing to have 12v available, in case of propane failure, but it is the 3rd option, the backup.
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Old 07-20-2021, 09:33 PM   #12
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Quote:
Originally Posted by KoolTraveler View Post
We are newbies awaiting delivery of our 1st RV (Class C). I have seen discussions in a number of forums on the safety of using propane while driving to operate the fridge. If you have safety concerns keeping the propane on while traveling, and assuming the batteries have the capacity to power the fridge, couldn't you keep the fridge operating and cooling by running it on 12V? Are the coach batteries being charged while the vehicle is operating as the chassis batteries do? Thanks in advance for helpful feedback.
Which Brand/Model of fridge??
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Old 07-21-2021, 04:48 AM   #13
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It is the Dometic 3 way, with the doors that open from both ways. Quite satisfied.
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Old 07-21-2021, 10:34 AM   #14
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Quote:
Originally Posted by Michel Paul View Post
It is the Dometic 3 way, with the doors that open from both ways. Quite satisfied.
That would be the RMD10

Just watch power selection.....it's different then other 3-way models

According to Dometic:
Automatic mode:
In automatic mode the refrigerator automatically selects the most
economical operating mode according to the following priority:
AC power
DC power
Gas


Loss of AC.....swaps to DC
THAT can run your batteries down quickly due to lack of battery charging

**Older models priority in AUTO
*AC
*GAS
*DC
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