3way fridge not working on 12V - Page 2 - Fiberglass RV


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Old 08-17-2009, 10:22 PM   #15
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These fridges are really critical when it comes to heater temperatures, especially when you're talking about low wattage ones. Look at www.RVMobile.com re: cooling unit diagnosis, and you'll get the idea. If it works on 115V then the cooling unit is likely good. Propane is a little more complex. Have fun, and for now, run with the inverter (but only if you're charging your 'House battery' on the road). The units involved in the propane system would probably be btu's/hr.
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Old 08-17-2009, 10:30 PM   #16
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Where on the coast? I would invite you to drop in, but we're away camping Aug 21-27 If your trip fits outside that, and you might come through Kelowna, get back to me before the 22nd.
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Old 08-18-2009, 11:12 AM   #17
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P=I(squared) x R. If your readings are correct you're actually running about 55watts, and NO it won't produce any cooling at that level. Have you verified the input volts to the 12V heater when it's operating? I've run your figures both ways and come up with 54-56 watts, not enough to make it cool. Try 'hot-wiring' the 12V element and let it have at least an hour to see if it cools at all. Above all, when you test it, make sure its level side-to-side (the fridge, not the trailer). To achieve 75 watts with 12v you need 6.25A. To get 6.25A at 12V, your resistance can't be more than 1.9ohms. Therein lies the problem. I doubt very much if you'd ever find a 12V heater for that fridge. So, unless you find a wiring problem with the element, you're probably done.
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Old 08-18-2009, 05:41 PM   #18
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yes, good points all. I am pretty sure the fridge is level enough, because it works in 110V and gas modes, and it is sitting in my garage on a concrete floor. I did have to raise the counter side of the body by 3/4 of an inch to get rid of sag after I put in a new axle last month, using a riser between the axle and the frame, but it is fairly level.

I am glad that you think it is most likely that the same refrigerant tubes run around all three heaters. This eliminates the refrigerant as the likely problem.

I measured the resistance across the 110V heater last night (very simple, just measured across the main 110V plug for the trailer when it was unplugged and the fridge was turned on to 110V and no other 110V applicances were on). The thermostat was set to maximum, but the reading was the same regardless when I turned the thermostat). The resistance came to 157 ohms, which gives me about 77 watts on 110V (using V-squared over R for power). This is consistent with the 75 watt rated power. When running on 12 volts, my battery was at about 12 1/2 volts, so the power for the 12V system is definitely much lower than the 110V system.

So, it seems that my 12 volt heater is drawing less than the 110V heater, and less than the critical amount required to supply enough heat to actually run the fridge. I agree with your calculations that I need 1.9 ohms resistance on the 12V heater to get 75 watts. I am about 0.6 ohms high. What is causing that slight resistance increase (he asks rhetorically)?

The wiring on the 12V side looks original and not in great shape, though not obviously corroded. It would only take less than one ohm over the eight feet or so of wiring to make the difference, so I will start by disconnecting the wiring to see if I can get a lower resistance with shorter wires. I will also try hot wiring the heater directly to the battery as suggested and see if that helps. If not, I will give up since the odds of finding a replacement heater are approximately zero (I can't even find an internet reference to this fridge, let alone spare parts!). However, if the fridge works that way then I will install new wiring and hopefully solve the problem.

I am optimistic because it seems to me that a bad heater would either break or short out, so perhaps this is only a wiring issue (he says hopefully!)

I will let you know how it all turns out. I hope to have a look at this tomorrow when I have a day off work.

Lloyd, we will be passing through Kelowna on the 30th, but only for an overnight visit to my youngest son's grandfather (not actually my relative, that is a long story). He is in Westbank but did not have to evacuate in the recent fires, though they were on 15 minute evacuation alert. Our main trip is to Hornby Island where we have relatives, then to Ucluelet (on the west coast of Vancouver Island) for some surfing with one of my older sons. So, thanks for the thought but perhaps we can catch up next time.

Thanks,
Rick G.
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Old 08-18-2009, 10:03 PM   #19
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It could be something as simple as a bad connection. I'm not sure how these elements are made, could be multiple strands of resistor wire, in parallel and you could have one strand open. One critical thing you haven't mentioned (or I didn't understand) is the is the voltage applied (right at the last connectors) when the 12V element is operating. To be honest I think using an inverter on the 115V system, is the best answer, at least for now.
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Old 08-18-2009, 10:50 PM   #20
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I am voting for all of the above...bad contact points in the electrical circuit drops voltage, in this old of a unit they should be bad or in the least inefficient anyway be suspicious...IF... the ohm readings are at the wires directly to the heater itself its to weak using ohms law... replace it they are cheap, raise the watts 20% if you can, the diameter of the heater element is more important than wattage within reason, another heater probe when installed is installed with a heat transfer paste on it. (ceramic) in older units...especially the French built ones which I think your refrigeration evaporator is...the paste is critical with these, it often sluffs off over the years making heat transfer less...the holding tube for the element rusts often making heat transfer even worse.

Safe camping, Happy trails.

Harry
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Old 08-19-2009, 06:57 AM   #21
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Sounds like you are nearing an end to the problem. Keep us updated
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Old 08-19-2009, 10:37 AM   #22
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Some heaters are wraparound, some cylindrical insert (those might be a b---ch to remove after all these years). I actually had to split the mounting tube on my old one (the element was rusted in). RVmobile.com has a lot of different types available. I agree, if you can get the parts, and get the old out easily, a little higher wattage would be better, at the expense of shorter battery life. Personally, I would rather go with your idea of running with the inverter, and leave well enough alone. You could probably re-use the old 12V supply wiring to power it. You really should read the info at www.RVmobile.com. Then you'll have a good understanding of how these things work, and what's critical. Ho-Ho-Ho!
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Old 08-21-2009, 11:47 AM   #23
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Thanks to all who chimed in. I tried to discover the root of the problem without removing the fridge on Wednesday, but was not successful. The access wires to the 12V heater still gave me about 2.5 - 2.6 ohms resistance. It appears that I will have to pull the fridge out and have a go at it, which I will do this winter.

For now I will run on the inverter when I need to get cooling from a 12V battery.

If I can replace the heater, all well and good. However, since the heater does actually heat, I may be able to make it work if I increase the wattage or heat transfer. Since the current and resistance are apparently fixed, the only ways to do that appear to be (1) improve the heat transfer to the cooling tubes as mentioned above to make sure it is maximum, or (2) increase the voltage from 12 V to 18V by adding a 6V battery in series. Since the only other things we have in the trailer that run on 12V are lights, this may work. However, I am not crazy about adding another battery, and may very well run through the inverter if it comes to that.

So, this brings the odyssey to a pause for now. I will try to pull the fridge around November to see what gives. Part of me wonders why I bother, since I have a work-around, but actually I get irritated by things that don't work properly, so I will probably keep at it until I have a solution some day.

Thanks,
Rick G.
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Old 03-26-2010, 08:06 PM   #24
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Well, today I finally got around to pulling the fridge out of the trailer. When I got a look at the back, I found that the heater element is a single copper cylinder about 4 1/2 inches long and about 5/8 inch in diameter, made by A.Birch & Co, somewhere in England. It slid easily out of the surrounding tube that attached to the refrigerant tubes. It was not held in by any paste or other sealant, and this seemed ot be the original configuration. It was next to the propane heater tube, which was also attached to the same refrigerant tubes. There was no significant rust anywhere that I could see. So, question 1 was answered, in that there is only one refrigerant tube and all the heaters heat up the same refrigerant.

The heater element has 4 wires sticking out of it, so both the 110V and 12V lines run the same heater. There are likely two elements in it, but there is no way to separate them out or replace just one.

I took the opportunity to clean the gas nozzle with alcohol and tidy things up a bit, then got to work on the 12V line. The ohms measurement across the 12V wires was 4 ohms, at the point where it connects to the trailer. This, as noted last summer, is not sufficient to get me to 75 watts. I need about 2 ohms to get 75 watts out of a nominal 12V line. So, I opened up the control panel where the 3-way switch and the thermostat reside. I disconnected the line that goes directly to the heater element and measured the resistance. It was 2.2 ohms across the heater element. This looked promising, as a 13 volt battery would give me about 75 watts. It also meant that I was losing 1.8 ohms across the 3 -way switch and thermostat wiring. Since both those components should be essentially 0 ohms resistance, it was probably bad connections.

So, I took all the connections apart and cleaned them. When I put the whole mess back together, I was getting 2.2 to 2.3 ohms across the whole system. This seems pretty close to the required load.

So, I replaced the all the parts and put the fridge back in the trailer. It seems to be working, but I will see how it does for a few hours. I put a glass of water in the fridge and will see if it gets cold. Anyway, I learned two things: if this doesn't work I can't replace just the 12V heater, and dirty connections can make a big difference.

All in all, I learned a lot today and am glad that i tried to fix it, even if it ends up not working.

Rick G in Alberta

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Old 03-26-2010, 08:37 PM   #25
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We have a 1999 Casita SD. I tried using our fridge on 12v on the very first trip in 2003 and it more problems than it was worth. It was the only thing I have found in 7 years that I didn't like about the Casita. I refused to even fool with it since. Propane when traveling and dry camping and 110v in parks, works like a dream.
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Old 03-27-2010, 12:35 AM   #26
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Make it work on propane. We had the trouble of the flame blowing out and the frig not working, while driving. A friendly RV store near Dayton, OH checked the LP pressure and adjusted it properly. It was 8, when it should have been 11 or something. Worked perfect -- and it was free.
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Old 03-29-2010, 04:51 PM   #27
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Make it work on propane. We had the trouble of the flame blowing out and the frig not working, while driving. A friendly RV store near Dayton, OH checked the LP pressure and adjusted it properly. It was 8, when it should have been 11 or something. Worked perfect -- and it was free.

Yes, the fridge does work fine on propane. I solved the flame-blowing-out problem by putting duct tape over the closest two of the four vent panels in the lower access door, which reduced the wind while driving. I put it on the inside so it does not look bad. There is still plenty of air from the other two vent panels and the entire upper vent so the gas flame has air to burn.

A good idea about the regulator. Our regulator is original (1974), so I will get it checked this year. However the furnace gives me a good steady pilot flame with a hint of roar, so I think it is probably OK.

It turned out that the coldest 12V setting on the fridge gave me a 1/4 inch layer of ice on the top of a glass of water after four hours or so, so I took that as a sign it was working (though not as efficient as the 110V). I plan to use the 12V generally only when gas is not allowed while travelling, such as on the west coast ferries. However, I am contemplating a fair size solar setup, so it may be used more often. However, usually we would use gas or 110V if available.

Regards,
Rick
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Old 03-30-2010, 09:08 PM   #28
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Ours had tape on the inside of the lower row, too. Thought this was from the factory.
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