3way fridge not working on 12V - Fiberglass RV


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Old 08-15-2009, 08:27 PM   #1
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Hi, I hope someone can offer advice.

I have a 74 Boler with an original Escort Mini 15, a small 3-way fridge. The fridge works great on 110 and gas (it will freeze milk if set incorrectly), but does not even slightly cool on 12 volt. I can't find any service or other documentation on this fridge.

The fridge has a small schematic diagram on it which seems to show separate heaters for 110 volt and 12 volt, but it is not totally clear. When turned on to 12 volt with the switch, the circuit draws 4.7 amps from the battery and has a resistance of about 2 1/2 ohms, which seems OK for this type of electric heater. After a couple of hours, the outside cover where the heater is gets quite warm, so i think the 12 volt heater is working.

Is it likely that there are separate heaters for the 12 volt and 110 volt circuits, and does this mean that there would be spearate refrigerant tubes around those separate heaters? It seems that the refirgerant must not be working around the 12 volt heater, but I am not sure that this make sense since the 110 volt heater should be right next to it, if not the same one.

The fridge has a thermostat for gas and one for electricity. It seems that the same thermostat controls both 12 volt and 110 volt operation, but I am not sure since the 12 volt is not working.

I have been running propane while travelling, but the gas tends to blow out while driving, and I would like to be able to run on 12 volts while driving. I can do a workaround to run on 110 volt while driving by using an inverter from the 12 volt supply and plugging in the 110 volt section of the fridge to the inverter, but I would rather have it working properly.

Your thoughts would be appreciated. We are leaving next week for an 8 day trip to the coast, but I have a couple of days to sort this out.

Thanks,
Rick in Edmonton
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Old 08-15-2009, 10:14 PM   #2
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I have a dometic fridge and I know it draws closer to 10 amps when on 12 volt.

Sounds like your fix of plugging the 110 into the inverter would work just fine. It may just draw a bit more because of the loss from the workings of the inverter.

You may be best to estimate a 10 amp draw per hour to operate the fridge. This isn't too bad if you have a large battery bank (240 amp/hours +) but, if you have a smaller group 24 or 27 then this would be too big of a draw on the battery (over 8 hours) especially if you are not charging the battery as you drive. In any case you would want to plug your battery charger in to re-charge your battery as soon as you arrive at your destination.(assuming your destination will have shore power available)

I simply use a cooler full of ice as I travel. Once I arrive at my destination I fire up the fridge on propane, wait overnight to allow it to cool and then transfer the cooler contents the next morning. If I am in a different spot every night then I just rely on the cooler and ice.
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Old 08-15-2009, 10:46 PM   #3
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Hi, I hope someone can offer advice.

I have a 74 Boler with an original Escort Mini 15, a small 3-way fridge. The fridge works great on 110 and gas (it will freeze milk if set incorrectly), but does not even slightly cool on 12 volt. I can't find any service or other documentation on this fridge.

The fridge has a small schematic diagram on it which seems to show separate heaters for 110 volt and 12 volt, but it is not totally clear. When turned on to 12 volt with the switch, the circuit draws 4.7 amps from the battery and has a resistance of about 2 1/2 ohms, which seems OK for this type of electric heater. After a couple of hours, the outside cover where the heater is gets quite warm, so i think the 12 volt heater is working.

Is it likely that there are separate heaters for the 12 volt and 110 volt circuits, and does this mean that there would be spearate refrigerant tubes around those separate heaters? It seems that the refirgerant must not be working around the 12 volt heater, but I am not sure that this make sense since the 110 volt heater should be right next to it, if not the same one.

The fridge has a thermostat for gas and one for electricity. It seems that the same thermostat controls both 12 volt and 110 volt operation, but I am not sure since the 12 volt is not working.

I have been running propane while travelling, but the gas tends to blow out while driving, and I would like to be able to run on 12 volts while driving. I can do a workaround to run on 110 volt while driving by using an inverter from the 12 volt supply and plugging in the 110 volt section of the fridge to the inverter, but I would rather have it working properly.

Your thoughts would be appreciated. We are leaving next week for an 8 day trip to the coast, but I have a couple of days to sort this out.

Thanks,
Rick in Edmonton


Hi Rick: From what you have explained it sounds like the thermostat is working because it is getting warm on 12 volt however the ohms reading seems low. If you can find out the wattage on the heater and you know the voltage is 12 volts you should be able to use ohms law and find out the proper ohms reading. The wattage should be on the heater which you should be able to wiggle straight up and out. As far as the 3 heat supplies the LP gas, the 110 volt heater and the 12 volt heater all do the same job to bring the ammonia solution to a boil which in effect cools the fridge. I would examine the 12 volt heater more closely as it sounds like it is not producing enough heat as per the ohms reading. For the LP blowing out, you might want to put a small piece of metal to block the wind but not enough to cause a venting problem or it could be a weak thermal coupler or weak flame {dirty burner or orfice}. Hope that helps and all goes well on your trip.
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Old 08-16-2009, 08:16 PM   #4
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The wattage should be the same 115v or 12 v You need X heat to do the work. Watts =Volts X Amps so the current on 12V will be 10X what it is on 120V. Most of these fridges run at least 150 watts so figure at least 15Amps, maybe 20, at 12V As for your solution of running on your inverter, I did exactly that last year, when travelling, on a 2-way trip to Toronto, via Seattle. All was fine, until the last day, when the 120v element shorted, and blew the inverter too. You might consider adapting an 'auto-igniter' to your fridge to reignite the pilot. Most 3-ways didn't work that well on 12V anyway, and they'll kill a battery in no time
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Old 08-16-2009, 09:37 PM   #5
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The wattage should be the same 115v or 12 v You need X heat to do the work. Watts =Volts X Amps so the current on 12V will be 10X what it is on 120V. Most of these fridges run at least 150 watts so figure at least 15Amps, maybe 20, at 12V As for your solution of running on your inverter, I did exactly that last year, when travelling, on a 2-way trip to Toronto, via Seattle. All was fine, until the last day, when the 120v element shorted, and blew the inverter too. You might consider adapting an 'auto-igniter' to your fridge to reignite the pilot. Most 3-ways didn't work that well on 12V anyway, and they'll kill a battery in no time
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Old 08-16-2009, 09:49 PM   #6
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Just looked up a supplier I knew of, and heaters run all the way from 95-325 watts
so current would be 8-30Amps at 12V. Can't say what yours should be, but that should give you an idea. Most thermostats wouldn't handle above about 15A. That's what failed originally on my old 3-way. The heavy current on 12V roasted the thermostat contacts, so they added a separate electric thermostat, and disconnected the 12V element. With new fridges and auto-ignite, 3-ways become 'special order'. Does the 'boiler' section ( the section directly above the burner) get as hot on 115v as it does on propane? What about on 12V? Do you charge your 'House' battery when on the road?
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Old 08-17-2009, 07:43 AM   #7
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I know yours is not a Dometic but all 3-way fridges are similar. The resistance spec for a Dometic 12V element is 0.66 Ohms +/- 10%. I suspect your heater is bad.

A high resistance (bad) heater will also have a low current draw (which you have).

If the heater is a 95W range your current draw should be in the 8 Amp range.

As your power rating for the AC and DC heaters should be about the same and your AC mode works I would suggest taking a current reading under AC mode. From that you can calculate what your wattage and current draw should be for DC. Post your numbers and I can do the math if you like.

I myself am having strange things happen with my fridge under 12V mode. Somewhere in my system I have a phantom 265 ohm load that pops up randomly and then disappears as soon as I start to troubleshoot. I feel like I am taking crazy pills.
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Old 08-17-2009, 07:57 AM   #8
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I myself am having strange things happen with my fridge under 12V mode. Somewhere in my system I have a phantom 265 ohm load that pops up randomly and then disappears as soon as I start to troubleshoot.
Is that the fridge in your Westphalia? If so there is a cooling fan connected to a thermo-switch thingy on the fins at the back of the fridge.
('scuse my electrickal terminoligy)
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Old 08-17-2009, 08:20 AM   #9
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Is that the fridge in your Westphalia? If so there is a cooling fan connected to a thermo-switch thingy on the fins at the back of the fridge. ('scuse my electrickal terminoligy)
Hey Roy. My current prob is actually in the fridge from my Scamp. My Westie came from the factory with only a poorly insulated icebox which is basically worthless unless you park next to an ice machine
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Old 08-17-2009, 09:28 AM   #10
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Hey Roy. My current prob is actually in the fridge from my Scamp. My Westie came from the factory with only a poorly insulated icebox which is basically worthless unless you park next to an ice machine
If Oliver's figure is correct, (and the figures tell me he is), The Dometic would draw about 18A. BTW, that works out to about 220 watts. If your 115V works good, here's an easy way to determine the correct resistance for the 12V heater. Measure the resistance of the 115V heater, it's easy, just turn the fridge to 115v with the thermo cranked to top and measure across the plug. Now divide the reading by 10. You'll be in the ball park.
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Old 08-17-2009, 11:39 AM   #11
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If Oliver's figure is correct, (and the figures tell me he is), The Dometic would draw about 18A. BTW, that works out to about 220 watts. If your 115V works good, here's an easy way to determine the correct resistance for the 12V heater. Measure the resistance of the 115V heater, it's easy, just turn the fridge to 115v with the thermo cranked to top and measure across the plug. Now divide the reading by 10. You'll be in the ball park.
Just to clarify. My Dometic is a 2201. 95Watt for the 115 VAC and 95Watt for the 12VDC.

IN 12V mode (assuming actual 12VDC) Current draw : Approx 8 Amperes.
IN 115 AC mode Current draw: 0.83 Amperes draw.
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Old 08-17-2009, 03:24 PM   #12
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Just to clarify. My Dometic is a 2201. 95Watt for the 115 VAC and 95Watt for the 12VDC.

IN 12V mode (assuming actual 12VDC) Current draw : Approx 8 Amperes.
IN 115 AC mode Current draw: 0.83 Amperes draw.

Oliver: We're both right, if the 12V element was .66 ohms, the current would be ~ 18Amp and watts ~ 220. Common in some Dometics. But as you say, yours is 95 watt, so ~8A is correct. But, as I said, most didn't work that well on 12V anyway.
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Old 08-17-2009, 04:42 PM   #13
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Well, I appreciate all the comments. I have made a little metal cover for the propane flame to block the wind while travelling, we will see how it works.

I took a look again at my fridge and tried to take the heater cover off, unsuccessfully. I can't remove the cover without taking the whole fridge out of its enclosure in the trailer, something I would prefer not to do. I was able to get the cover off far enough to see that it is a tall vertical assembly, with the propane burner at the bottom, and the electrical heaters above it, with some finned tubes above that. If the 12V heater is separate from the 110V heater, it would be the top one, as it seems that the 110 volt wires go into the assembly at a slightly lower point than the 12 volt wires, where I cannot get at it from the trailer outside access panel.

The fridge plate says that the electrical is rated for 75 watts, and it has a rating of 430 for the propane (not sure what units it is using for propane but this was 1974 when it was made). My estimate of the actual wattage is about 55-57 watts (P=I2R). Also, as noted above the heater cover gets warm, and there is fiberglass insulation inside. The heater on 110V seems to get about as warm, but it is hard to tell because of the length of time that passes between tests. On both settings, the cover is noticeably warm but not dangerously hot. So, although the DC heater is not working at full rated power, it does appear to be working enough that I should get at least some cooling. I will measure the AC current when I get back to it on Wednesday, that will give me a good idea of whether the 110V and 12V are operating approximately the same.

Which brings me back to my other question and theory (which shows how little I know about fridges). Is it likely that the fridge has a different 12V heater than the 110V heater, and if so is it likely that the refrigerant tubes are working for the 110V and gas, but not the 12V? I may have to pull the fridge out of the trailer to have a look at this, but I would like an idea whether this is even reasonable? If there are separate refrigerant tubes that are possibly blocked, it may be possible to do something about that part of it.

Thanks,
Rick
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Old 08-17-2009, 09:22 PM   #14
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Which brings me back to my other question and theory (which shows how little I know about fridges). Is it likely that the fridge has a different 12V heater than the 110V heater, and if so is it likely that the refrigerant tubes are working for the 110V and gas, but not the 12V?
Hey Rick. Yes, your fridge probably has different 12V and 115AC heaters. Probably the same refrigerant system for all three modes of operation. There is probably something else going on. The fact that your current draw is low probably indicates your DC heater is questionable.

I would also check the normal stuff. Make sure your fridge is level. Make sure all of ducting and baffling is where it is supposed to be. But that will probably require pulling the fridge.
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