BrianR Posted July 14, 2009 Share Posted July 14, 2009 I have realised that the problem I set out in an earlier post was not in the neon indicator on the 12V switch but that the fuse under the bonnet had blown. The fridge is an Electrolux RM4213S, installed 1996. This is the small 240V/gas/12V fridge with electronic ignition. Having replaced the fuse I checked that at the fuse there was 13.5volts (under load), but the current was only 0.8 amps. I checked these same readings at the 12V switch on the fridge and they were the same. When I disconnected the return from the neon the current dropped to 0.7 amps. The resistance across the element was 1.3 ohms, which seems to me about what one would expect, as the fridge is rated at 120 watts, according to the plate, or 100 watts according to the manual. Can anyone sugest why the current should only be 0.8 amps when the element seems to be OK? If the problem were with the gas or mains I would check to see how well the fridge was cooling, but that is more difficult on 12 volts, and also, I am not sure what would be "normal" on 12 volts. Any help would be greatly appreciated. Link to comment Share on other sites More sharing options...
Guest Tracker Posted July 14, 2009 Share Posted July 14, 2009 I may be wrong but as I recall early caravan fridges were not designed to refrigerate by bringing the temperature quickly down but only to maintain temperature once the fridge had been cooled to operating temperature by gas or mains? But I could be wrong and this maybe only applied to earlier ones - I can't remember that far back! Have you tried putting a thermometer in the fridge and then running the engine for halt an hour, or driving, with the fridge on 12v to see what, if anything, happens? I seem to recall that the 12v battery drain is about 8 or 10 amps? I assume that on gas or mains it cools OK? That said I seem to recall that they were never that wonderful at getting really cold anyway - but better than nothing! Temperature checks on all three running modes may be the best way to ascertain what is not working? Don't take this as gospel as my memory is not always as accurate as I would like it to be - but it might help? Link to comment Share on other sites More sharing options...
vindiboy Posted July 14, 2009 Share Posted July 14, 2009 You do know that 12 volt on Fridges only { should only } work when the engine is running ???? Link to comment Share on other sites More sharing options...
rossko Posted July 14, 2009 Share Posted July 14, 2009 No I didn't know this. Still being a novice at all this I am confused why the fridge has an option to select battery power only. Does this mean the leisure battery then or not. We chill our fridge down the day before we leave but have never arrived anywhere over 50 or so miles away with the fridge still really cold. The silver fins are always wet not icey. Can anyone advise whether this is a fault as it doesn't seem right to me. Link to comment Share on other sites More sharing options...
hymer634 Posted July 14, 2009 Share Posted July 14, 2009 Have you measured the voltage at the 12V element .? As the earlier poster said there should only be 12V there when the engine is running or the ignition switched on. The fridge is usually supplied from the vehicle battery. There should be a relay to control the supply to the fridge, operated by a feed from the alternator or a wire from the ignition switch. It is possible that this relay or a fused supply to it is faulty. There may be a fuse in the igniton/alternator control wire to the relay and a large fuse in the main supply. Link to comment Share on other sites More sharing options...
BrianR Posted July 14, 2009 Author Share Posted July 14, 2009 The fridge works properly on gas and 240 volts. The 12 volts comes from the vehicle battery when the alternator is working, i.e., the engine is running, not the leisure battery. As the 12 volts is getting to the fridge, I don't see how the relay or the fuse could be faulty. The current and voltage were measured at the switch end of the wires going to the element - it is not possible to measure it any closer to the element, without cutting in to the insulation on the wires. Link to comment Share on other sites More sharing options...
machinehead Posted July 14, 2009 Share Posted July 14, 2009 BrianR - 2009-07-14 9:59 PM - it is not possible to measure it any closer to the element, without cutting in to the insulation on the wires. This makes me wonder how you are measuring the current (amps)? Stripping the insulation would not let you measure current, only voltage. You must disconnect one leg of the supply and put your ammeter in series. An easier method is to simply remove the fuse and bridge across the fuse holder with your ammeter. Be careful though. If there's a short circuit your ammeter will allow a lot of current to flow if it doesn't have its own internal fuse. (I think the poster above its right in that the 12V will only maintain the temperature in the fridge while the engine is running.. You must cool it initially on 240V or gas) Hope this helps. Link to comment Share on other sites More sharing options...
BrianR Posted July 15, 2009 Author Share Posted July 15, 2009 machinehead - 2009-07-14 10:41 PM BrianR - 2009-07-14 9:59 PM - it is not possible to measure it any closer to the element, without cutting in to the insulation on the wires. This makes me wonder how you are measuring the current (amps)? As I said, I have measured the voltage, current and resistance at the 12V switch on the fridge, where I can disconnect the wires. The current at the input to the switch was 0.8 amps and at the output to the element it was 0.7 amps. The difference is, presumably, the current consumed by the neon Link to comment Share on other sites More sharing options...
hallii Posted July 15, 2009 Share Posted July 15, 2009 Using a known good 12v battery connected to the fridge side of the switch (switch not used) and let it run. The cooler plates should get frost on them after about 1 hour or so. Don't keep opening the fridge to look! If after 2 hours or so there is no frost you have a problem. The element may show a given resistance cold but when it warms up it may be something else maybe even open circuit. 120w at 12 v is 10 Amps. So the resistive load would be about 1.2 Ohms at 12v. If you are getting less than 10 amps reading then either the meter is wrong or the resistance is varying as the element heats up. They always work better on gas or mains, but will get quite cold from start up just on 12v, it just takes a bit longer. Make sure the fridge is somewhere near level, they work by evaporation of a liquid into gas and the liquid needs to run down to the bottom to start all over again but if the liquid can't run away then the cooling efficiency is very poor. Link to comment Share on other sites More sharing options...
machinehead Posted July 16, 2009 Share Posted July 16, 2009 The resistance figure you measured seems OK for the wattage. So, if you are drawing only 0.8 amps then there must be another resistance in the circuit which is adding to the element resistance and reducing the drawn current. (Should be around 10A) Someone mentioned the element resistance chaging as the temperature changes. That is possible, but maybe a little less likely than a high resistance in the circuit wiring. I'd look for a bad connection in the 12V circuit. Might be a bit of corrosion (spray WD40 or similar), could be a loose connection? Remember, if there IS a poor connection you could still read the full voltage so don't be fooled by that. Hope this gets you a little further to solving your problem. I'll come back in a day or so to see how you get on. :-D Link to comment Share on other sites More sharing options...
BrianR Posted July 16, 2009 Author Share Posted July 16, 2009 Thanks for these suggestions, now at least I have something else to try. Will keep you posted. I don't have a really good spare battery, but I do have one that I could use. Would it be OK to connect it up to a charger at the same time? Link to comment Share on other sites More sharing options...
machinehead Posted July 16, 2009 Share Posted July 16, 2009 BrianR - 2009-07-16 11:08 PM Thanks for these suggestions, now at least I have something else to try. Will keep you posted. I don't have a really good spare battery, but I do have one that I could use. Would it be OK to connect it up to a charger at the same time? Sorry, but if you already know that the circuit resistance is 0.8 ohms then you are wasting your time trying out with a spare battery. Anyway....regarding the charger - they are all different rated currents so it depends on your charger. It would be best if it could deliver a constant 10A then you won't drain your battery. However, based on what you say, it would be a fruitless exercise. Link to comment Share on other sites More sharing options...
BrianR Posted July 18, 2009 Author Share Posted July 18, 2009 I think I will try the battery suggestion anyway, just to be sure, although I think I will put in an inline fuse to be on the safe side, as it may have been a faulty element that caused the fuse to blow when it got hot. Unfortunately I am now going away in the van for a week, so I will see how the fridge behaves on the journey and then test it out with a battery when I get back, if nothing becomes clearer on the journey. As I said, I will keep you posted. Link to comment Share on other sites More sharing options...
machinehead Posted July 19, 2009 Share Posted July 19, 2009 Fair enough. Have a good holiday. Link to comment Share on other sites More sharing options...
BrianR Posted July 30, 2009 Author Share Posted July 30, 2009 I'm back and have at last got round to revisiting the problem. On the trip the fridge didn't work at all on 12 volts. I have now connected the 12 volt heater element to a battery directly and, joy upon joy, it worked. The current measured 9.5 amps initially, dropping to 8.5 amps as the element warmed up. In 2 hours the temperature in the little freezing compartment had dropped from 20C to 0C. From this I conclude that the problem is in the negative path somewhere. I can't follow where the wire goes, so I will put in a new wire down to a point nearby on the chassis - 4mm should be enough, shouldn't it? hopefully that will be the end of the problem. Thanks, everyone who posted, for your help. Link to comment Share on other sites More sharing options...
Brian Kirby Posted July 31, 2009 Share Posted July 31, 2009 Don't want to "grow" your workload, but might it not be worth seeing if you can find out what blew the fuse that first alerted you to the fridge problem? I'm just wondering if you have some loose wires somewhere, possibly in a 12V junction box, and if that may be the root cause of both problems? Link to comment Share on other sites More sharing options...
BrianR Posted July 31, 2009 Author Share Posted July 31, 2009 There was me, thinking that I could get away with being an ostrich! I agree with you, Brian, but I have checked all the accessable points and all seem OK, so I am going to see if it happens again. I am now trying to follow the path of the negative return wire, to see if I can find the poor connection, as I have not yet found a route for a new wire to replace it. Link to comment Share on other sites More sharing options...
Clive Posted July 31, 2009 Share Posted July 31, 2009 The fridge should take between 8 - 10 amps on 12 volts but only when the engine is running and the alternator charging. A relay is used to control the supply to the fridge and the relay coil is controlled by the alternator. The diagrams on this link might help. http://www.motts.org/SPLIT%20CHARGING%20SYSTEM.htm Good luck Clive Link to comment Share on other sites More sharing options...
BrianR Posted August 1, 2009 Author Share Posted August 1, 2009 I have tried the fridge again using the normal 12 volts from the vehicle battery (with the engine running) and with a temporary new negative lead to the chassis "earth" point and the current taken was again around ½ an amp. After more thought, I took the 12 volt fridge switch out of the circuit and the current leapt up to the expected 10 amps or so. I then investigated the switch and found that the fitter who had replaced it during a habitation check had wired it incorrectly. I put it back with the correct wiring and everything is now working. As my Dad used to say "If thou wants a job done properly, do it thy sen"! Link to comment Share on other sites More sharing options...
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