Dometic RM7291L on 240v trips RCD

Discussion in 'Fridges & Ovens' started by Spriddler, Jun 9, 2018.

  1. Spriddler

    Spriddler Funster

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    Fridge runs fine on 12v and on gas and all other 240v appliances work as they should.
    When on EHU to the house and the fridge is switched to 240v the house RCD instantly trips out *. I suspect a short/fault in the 240v heater element. Can anyone advise the resistance of a good fridge heater element (or a busted one come to that but I suppose it with be either a dead short or infinite - open circuit).
    I've had a browse on t'internet but it seems the heater element is unavailable which I suppose means a new fridge if I can't get an element from a caravan breaker or use one from a similar fridge.
    It may not be the element so any other suggestions welcome.
    Going away to France for 2 weeks on Saturday next :-(
    Ta.
    *My electrician neighbour tells me that the house RCD trips before the caravan because the caravan RCD has a 40 millisecond delay built in by design whereas my house RCD (he rewired my house 3 years ago) is instantaneous.
     
  2. SandraL

    SandraL Funster

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  3. Spriddler

    Spriddler Funster

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    Thanks.
    I don't think the 'L' will be significant as all the heater pics I've seen are identical. The 'L' may just stand for 'left handed door' although the hinges can be set up for left or right opening.
    I found about half a dozen suppliers on Google but all were 'Stock unavailable'.
    Should've gone to eBay first (I often do) but one can never be sure of quality with pattern parts from unknown suppliers on eBay and they are a bit fiddly to fit so only wanted to do it once! I was hoping to buy a genuine Dometic/Electrolux part so only browsed reputable caravan fridge parts suppliers. However I'm sure that Dometic buy their heaters in, and more likely than not they'll all have come from China anyway.
     
    Last edited: Jun 9, 2018
  4. DBK

    DBK Funster

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    The resistance could be a few hundred ohms. That is based on the assumption the wattage on mains is also a few hundred. No doubt the spec for your model will be somewhere but if you measure the resistance, and also check live and neutral to earth anything in low figures (tens or less) suggests a short. :(
     
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  5. Spriddler

    Spriddler Funster

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    Thanks DBK. I'll set to with the meter tomorrow and check it all out.
    Worst case I can run it on gas whilst away as I have a refillable Gaslow system and the 12v will run it whilst I'm driving.
    I did try to remember my physics from 50 yrs ago and reckoned that my 120W element on 240V draws about 0.5 Amp and 120W divided by 0.5 = 240 Ohms but I think I may be completely wrong with my formula.
     
  6. tonyidle

    tonyidle Funster

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    If it trips the RCD then the first check of the element should be for leakage to earth (element disconnected, check from each wire to the element case). It's also worth seeing if the RCD trips once the element is disconnected - there are a number of connections that might be the problem rather than the element. It can get quite wet behind the fridge.
     
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  7. Spriddler

    Spriddler Funster

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    Great Tony. Thanks. I'll check both those points. In fact it is a bit rusty around the back (I'm working on it through the exterior lower vent aperture) and suspect that corrosion may be causing trouble, e.g. shorting one of the live element wires to earth. It'll all get a good clean up, especially the connectors, which on the heater element wires are surprisingly just simple Lucar type crimped-on spade connectors.
     
  8. namwaldog

    namwaldog Funster

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  9. Richard and Ann

    Richard and Ann Funster

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    R=V/I
    So it will be about 480 ohms. Irrelevant if it has an earth fault but you can still check it.
     
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  10. Spriddler

    Spriddler Funster

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    Thanks.
    I have the Dometic Operating and Installation Manual and have looked at the wiring diagram but it doesn't have any relevant electrical spec'ns, a spares list or fault-finding details.
    I'll have a poke around with the meter (EHU disconnected!) in an hour or so.
     
    Last edited: Jun 10, 2018
  11. namwaldog

    namwaldog Funster

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  12. Spriddler

    Spriddler Funster

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    Ta. I'll know if it's the right one when I get the old one out. It certainly has two brown A.C. wires and one Earth but then I guess it would need to be earthed as it's mains voltage and the 12v D.C. element needs only two wires (although confusingly the wires on the A.C. and the D.C. elements are also brown!). All should be revealed soon and I'll report back.
     
  13. Enword

    Enword Funster

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    We had the same after a winter lay up, I had 2 tips given to me, 1 leave it on gas for a day & then try it on 240, the other was in my view dodgy so wont mention it:p so I left it on gas & hey presto its been fine ever since, sparky said the powder inside the element will leach moisture & leak to earth, just a thought(y)
     
  14. Spriddler

    Spriddler Funster

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    Ta @Enword Yes, this was first use after the winter lay-up. I did run it on gas but only for an hour just to check it was working on gas.
    (My 40 something sons would appreciate you not mentioning the dodgy check as they have already been exasperated for many years with my own dodgy bright ideas ;) Even when they were toddlers I made 'them' a go-kart without brakes from an aluminium ladder and a lawn mower engine, hurtled down my cul-de-sac, couldn't stop or turn at the end and went straight up a drive smashing a glass porch front door :rolleyes: )

    Fridge checking delayed due to unexpected arrival of visitors but I'd rather have no fridge than no visitors :)
     
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  15. TeeMyob

    TeeMyob Funster

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  16. Spriddler

    Spriddler Funster

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    All of the several pukkah refrigeration/caravan suppliers listed them but all showed no stock. Found half a dozen offered on eBay from 'general' dealers at around £35. I can only assume that since eBayers are selling them 50 quid cheaper the pukkah stores don't bother stocking and trying to sell their 80 or 90 quid ones any more.

    Update.
    Typical! Whilst faffing about with the test meter with the fridge running on gas that too went off :rolleyes:. Traced that to the permanent 12v supply failing due to dirty contacts and intermittent supply at the multi-way connector plug which sent the gas control valve into its default 'closed' position (and no igniter clicking when trying to re-light the fridge). I just pushed the connector plug on and off its pins 20 times which seems to have cleaned the contacts and all is well now on gas.
    Moving on.
    Whilst switching the front selector knob between 'Off' and 'Gas' I inadvertently turned it one click too far to the '240v' position and to my surprise it didn't trip the RCD. Left it running on 240v and the fridge cooled but after about 15 mins the RCD did trip. I'm assuming that when the 240v heater gets hot its internal insulation breaks down and the element coil shorts out to earth. I'll give it another go on 240v after the gas has run for a few hours which may dry the 240v element as @Enword suggested.
    I think to replace the 240v element I'll have to move the fridge out a bit as its 240v wires disappear up out of sight and I'd need the tiny hands of a 3 yr old and a triple jointed arm to get anywhere.
    At least I've now sorted reliable gas operation so no panic!
    Thanks for all the help.
     
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  17. namwaldog

    namwaldog Funster

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    Don't know if it will help but in my recent foray into "fridge fixing" I had the same problem space & access wise and found that by taking off the white plastic mounting plate that the vent cover clips onto (about 12 s/s screws) it afforded me quite a bit more room. Its a bit sticky with the not setting mastic .

    dometic-ls300-inner-frame-only85310.jpg
     
  18. Spriddler

    Spriddler Funster

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    Yes, taking off that frame would be my next step once I decide to see if an exploratory and blind grope up inside would convince me to replace the 240v element without having to move the entire fridge out a foot. I could simply cut the wires off the old element, disconnect their other ends from the control box and leave them in place as I'd only otherwise be throwing them away with the old element. A new element has moulded in wires (2 power and 1 Earth) which could be connected to the control box. Unfortunately all the connections (about 8 in total) are made via a 'special' and rather delicate multi-pin connector plug which isn't really designed to be re-used/rewired. I've looked for a replacement on the Farnell website but a) I don't know its precise description, and b) there are literally thousands in the Farnell catalogue.
    I've stopped now whilst ahead as it has been working fine on gas all afternoon. I have semi-permanent honeycomb patterned knees and back ache from working through the lower vent 'letter box' all afternoon :rolleyes:
    What fun!
    (What fun?)
     
  19. Richard and Ann

    Richard and Ann Funster

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    On ours if you disconnect the gas pipe it slides out easily, the wires have plenty of slack on them. Don't be scared to get it out :eek: (y)
     
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  20. Spriddler

    Spriddler Funster

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    The 'Edit' option had timed out so ignore the paragraph in my post above re the special multi-pin connector plug as that connector is only the 12v circuits not the 240v circuits. I've just realised that the 240v heater element wires connect to the mode selector switch on the front of the fridge fascia panel). :rolleyes:

    Brain fade - been thinking too long and hard.
     
    Last edited: Jun 10, 2018
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