spartan3956 Posted August 25, 2008 Share Posted August 25, 2008 I am about to go to France and have a fridge problem on an RM6501 fridge freezer. The gas burner lights and gives a blue flame on 230 v the heater elements get hot and 12 volt on the move is ok but the frige and freezer do not go cold . Has anyone idea`s on what is wrong with it. Link to comment Share on other sites More sharing options...
Brian Kirby Posted August 25, 2008 Share Posted August 25, 2008 You need a quick fix, as I think your fridge has lost its refrigerant. You'll need to find a reasonably local Dometic service engineer. If you don't know of one, try contacting Dometic's customer services. They have recently moved to Blandford St Mary, and their website is a bit less helpful than it was, but there is a general enquiries number. They should have a list of service engineers. Link to comment Share on other sites More sharing options...
spartan3956 Posted August 25, 2008 Author Share Posted August 25, 2008 Brian Thank you for your quick reply i assume the system has a leak, I might go for a re gas and sort it out properly when i return. Peter Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 26, 2008 Share Posted August 26, 2008 Is it actually possible to get a Dometic 3-way fridge 're-gassed', as I don't think I've ever heard of it being done? If it is possible, then it would be worth knowing. Link to comment Share on other sites More sharing options...
hallii Posted August 26, 2008 Share Posted August 26, 2008 I had problems a few years back and the fridge could (or would not) be regassed. I had to have a new unit, actually twice, and that is the purpose of my post. Make sure that the reason for the leak is determined before any repair, mine was due to vibration / stress at the flue cracking the pipework, due to insufficient screws holding the fridge rigid. Geoff Link to comment Share on other sites More sharing options...
spartan3956 Posted August 26, 2008 Author Share Posted August 26, 2008 To update on this problem i have spoken to a vehicle refrigeration engineer who said that some time these type of fridges have problems with the gas settling and fail to cool, believed an amonia type gas. His comment was to get the fridge out and place it upside down for 24 hours. and then replace it and it should be fine. This fridge has been standing for 12 months so it could be feasible that he might just be correct, So my fridge is upside down and it did make a gurgling noise as i tipped it over so there is fluid in the system. they are not heavy although big and you do need to be qualified in gas and electric installations. Tomorrow i will be able to say if it has done the trick. I have previously heard of people giving them a good shake but but i have been open minded about the results. so here goes. Link to comment Share on other sites More sharing options...
Brian Kirby Posted August 27, 2008 Share Posted August 27, 2008 To Derek, yes they can be re-gassed - provided the reason for gas loss is only a poorly made seal and not perforated pipes.To Peter, the same source of information - a man who trades from Chichester as Cathedral Services and spends most of his time servicing Dometic medical fridges - advsied that the "turn the fridge upside down" lark was largely a waste of time. The refrigerant passes from liquid to gas, and then back again to liquid. There is no pump, and at any time part of the cricuit contains refrigerant in the one state, and other parts in the other. As it changes state it either absorbs heat from its surroundings, or releases it back to them. Hence the inside gets cold, and the back gets hot. Circulation is driven by a simple thermosyphon, which is why a gas flame can work the fridge, and why both electrical supplies drive heating elements.The main reason, apart from lack of gas, for these fridges to stop working is corrosion scale blocking the circuit. This blockage can sometimes be cleared by inverting the fridge but, since the scale has not been removed from the circuit, it is likely to accumulate again with the same result. May take hours, days, or even possibly years but, if corrosion is the problem, the fridge is going to fail again, sooner or later. The only remedy, unfortunately, is a new fridge. A "proper" fridge engineer should know this. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 27, 2008 Share Posted August 27, 2008 The 'inversion' ploy is often advised for reviving dead fridges (I've suggested it myself in the distant past on these forums.) As Brian says, sometimes it works and sometimes it doesn't and, even the fridge does perk up as a result of being placed upside-down, there's absolutely no guarantee how long it will keep going. In this instance, as the fridge has been removed for attention, it's got to be worth a try. If, after inversion, the fridge proves able to cool, then it's reasonable to assume that there's still refrigerant in it even if it's not circulating. Most complaints about fridges having heating-units that appear to be working OK but the fridge just doesn't cool, have seemed to relate to older appliances. But a 6-Series fridge/freezer is (I think) reasonably recent. Link to comment Share on other sites More sharing options...
Pat Posted August 27, 2008 Share Posted August 27, 2008 Hi I was told many years ago by a quite learned refridgeration engineer friend that these fridges contain a mixture of gases and so refilling is not possible. He also agreed that the cause of such a fridge not working was invairably due to a blockaged caused by internal corrosion. Regards Pat Link to comment Share on other sites More sharing options...
spartan3956 Posted August 27, 2008 Author Share Posted August 27, 2008 Ive replaced the fridge and it is still U/S so the next stage is a new one. Anyone any idea`s where i can get one at short notice . Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 28, 2008 Share Posted August 28, 2008 I believe the RM-6501 s no longer available and that the replacement model is the RM-7601L. (You should confirm this yourself to be certain and, if possible, check whether any 'structural' modifications will be needed to allow it to be fitted.) For potential suppliers, I suggest you GOOGLE-search webpages from the UK using "Dometic RM-7601L" (and/or "Dometic agents") as the search term. You could also try CAK (www.caktanks.com) or Miriad Products (www.miriad-products.com) as I know they market Dometic appliances. Not sure how available these things are at short notice, but you might strike lucky. Price will be unpleasant! Link to comment Share on other sites More sharing options...
Geoff Cole Posted August 29, 2008 Share Posted August 29, 2008 There seems to be some confusion as to whether it is possible to replace lost refrigerant in an absoption type unit. Refrigeration was my field years ago and I hope to clarify the situation. It is not possible to regas an absorption type refrigerator they do not contain gas as do compressor type refrigerators,which contain a single gas, and regassing is straight forward. Absorption units contain a mixture of 3 components to make them work, water, ammonia and hydrogen in very precise quantities, and an anti corrosion additive usually zinc chromate. The problem is that it is virtually impossible to replace the components in the exact quantities, and the manufacturers of these units do not give the required information to make this possible coupled with the very expensive equipment neede to carry out this work, the cost would be prohibitive. The construction of the unit is of a completely sealed steel unit, there are no seals or valves to leak. the pressure on the condenser side of the evaporator "U" tube is in the region on 200psi so if a small leak does occur then the mixture of gasses will be lost very quickly. When working with refrigeration plants I sometimes used to work with large commercial absoption refrigerators and we sometimes had to turn them upside down after a period of non use this would help remove any vapor lock in the system and after a day or so they would usually start working again,but this was quite a few years ago. The main reason for a modern absorpsion type refridgerator to stop working if the heating source is ok is that there is corrosion in the absorber, or generator or there has been a loss of pressure, if the unit has stopped working whilst in service with the heat source working then it is usually due to an irrepairable fault in the absorber unit. If the unit has been lying unused for a period and does not work then turning it upside down for at least 12hrs and then trying again it may start working and continue so for a while but the performance may not be as good as it should be so a replacement will be on the cards. These types of refrigerators give many years of excellent service, and the newer models are a great improvement on the old ones. Some large fridge freezers in America use lithium bromide instead of ammonia and any tampering of these is definately a no no. hope this clarifys the situation. Geoff Cole Link to comment Share on other sites More sharing options...
colin Posted August 29, 2008 Share Posted August 29, 2008 A little aside which I hope doesn't detract from the more serious side of this problem. As a child I remember we had a Fridgidaire (or similier) you know the type which is popular as a retro look nowadays, once or twice a year it would need dragging to middle of kitchin and be turned end over end to clear vapour lock. A friend has the oldest fridge i've ever seen, it was originaly parrifin powered but has been converted to electric, this going strong Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 30, 2008 Share Posted August 30, 2008 Geoff: Thanks for the explanation. The manual for my Dometic RM-7651L fridge/freezer defines its coolant as ammonia, with sodium chromate being employed for corrosion protection (1.8% of the solution). I had a vague recollection that Dometic's website used to carry a FAQ section warning that their absorption fridges couldn't be 're-gassed', which is why I queried this point. Brian: It might be worth you re-exploring with your source at Cathedral Services the ability to re-gas these appliances as there's (apparently) a clear conflict between what you've been told and Geoff's expert advice. Link to comment Share on other sites More sharing options...
rowley Posted August 30, 2008 Share Posted August 30, 2008 Spartan, you could try Autocraft at Chesterfield. www.autocraftmotorcaravans.com They advertise in MMM Link to comment Share on other sites More sharing options...
spartan3956 Posted August 30, 2008 Author Share Posted August 30, 2008 Hi Thank you for all your informative replies. I have spoken to our local Dometic service engineer who stated that they cannot be re-gassed, he also asked if there are any signs of yellowing at the back of the fridge ie this would denote coolant leakage. there isnt any i can see. The mixture of refrigerant can over time of inactivity crystalise and block the tubes some are quite small this is probably the cause as the fridge has ben standing some time. He did state that inverting the fridge may sort the problem as the crystels will return to their liquid state but it should be for a number of days unfortunately my time scale does not allow for that. My other option is to replace the whole of the refrigeration unit containing the refrigerant this would mean a complete rebuild the cost of the part would be around £260 this is an option i will explore when i return. I may just bite the bullet and get a new model a quick visit to a sales pitch with a tape measure will give me an idea of the compatability. I have temporally purchased a sunncamp portable 40 litre fridge which will work off 230v ,12v and gas this should see me through the holiday. Again these are absorbsion and only work on a level surface my motorhome is parked on a slope which i feel may have caused the problem. what is the betting that the fridge works when it hits the first speed bump i will then have a great outdoor wine cooler. Off to France tomorrow. Link to comment Share on other sites More sharing options...
Geoff Cole Posted August 30, 2008 Share Posted August 30, 2008 Derek, You are quite right the refrigerant used in these units is ammonia ,the other 2 components make it work so the quantity of each of the 3 components is very critical. I will give brief explanation of how the 3 components combine Liquid ammonia in an atmosphere of hydrogen will evaporate and cause cooling. The evaporating temperature of the ammonia depends on the partial pressure of the ammonia vapor which mixes with the hydrogen as it evaporates. The evaporated ammonia mixed with the hydrogen flowes to the absorber, here the ammonia gas is soluble in water but the hydrogen is not. Therefore the ammonia is disolved leaving almost pure hydrogen. Hydrogen is much lighter than ammonia, therefore a column of hydrogen is lighter than a column of ammonia and hydrogen. This causes the hydrogen to rise to the top of the evaporator as the heavier of the 2 gases settles from the evaporator to the absorber. regards geoff Link to comment Share on other sites More sharing options...
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