Dometic fridge

[chris]

We have an occasional "clunking" noise in our 3 year old fridge. It is not the clicking noise when the pilot light relights. At one point it turned the electric switch off on the fridge but it worked again after travelling on battery. I have a video of the noise but doubt if it will work on the forum. It might be only when on electric but I can't be sure. It is very random. Someone mentioned the "relay" . Any ideas pleas.

[Brian Kirby]

It would help if you could give the fridge type and model number. The fridge runs on 12V electricity, 230V electricity, and gas. I'm assuming this is when on 230V electricity?

 

You say the switch was "turned off". Is this a mechanical switch, or a virtual switch on the fridge control panel?

 

Where were you when you experienced this behaviour?

 

We had something that sounds vaguely similar with our (Thetford) fridge on one French site a while back. It turned out to be due to low voltage on the site causing the fridge to switch from mains supply to gas, and then back when the supply voltage reverted to normal. I seem to remember that the critical voltage was 210V. Anything less, and the fridge switched to gas, and then back to mains when the voltage rose. Could low site voltage be the cause?

[chris]

Sorry Brian. No access to van at moment but it is a dometic tall fridge freezer with AUTOMATIC selection and 3 years old. the electric button light on the control panel came off electric at the time and tried to go to gas. I kept putting it back to electric selection but it wouldn't stay on even though there was electric in the van. We were abroad as we have done a 10 week tour to Croatia Hungary etc so this did occur on European sites. I should have made note of when it occurred but I do know the last incident was in Germany on a motorehome dealers aire and the electric was pretty good there . Will try and get model type soon. It happens randomly. Chris

[Brian Kirby]

If you were mainly using EHU, I assume you will have used several other hook-ups after leaving the German dealer's aire? So, if you didn't have problems when on EHU elsewhere, I'd be inclined to search for the Voltage range your Dometic fridge is designed to accommodate.

 

It isn't a case that the power shuts off and everything stops working, just that the fridge switches to gas when the supply Voltage falls below it's pre-set minimum level. If a site is busy, with everyone using electricity, the number of users connected can cause the Voltage to drop, possibly below the fridge's range. Thunderstorms can also have odd effects on supply Voltage. If you find that the set Voltage range for the fridge isn't far above the theoretical standard 230V, I'd be inclined to put the problem down to intermittent low voltage, unless you keep getting instances. Then, I'd start thinking about a possible bad connection in your EHU, in the consumer unit, or at the fridge itself and, if all those are tight, I'd begin to wonder about the fridge controls/PCB.

 

The UK standard is 230V +10 - 6 ( so, 224V - 240V), whereas much of Europe is 230V +6 -10 (so, 220V - 236V). But see also here: http://tinyurl.com/y7x2mrdx What is nominally presented as 230V, often is not!

[chris]

Thank you Brian for a very thorough answer. On reflection the aire was full and it could have been the voltage dropping. I will watch it closely and hope that was the case. We usually run on gas and off eHu so will keep a close eye ( or ear) to it. Chris

[Robbo]

The OP could purchase a plug-in AC voltage display to check site voltage in future. Available on ebay for about £5:

 

http://www.ebay.co.uk/itm/AC-80-300V-LCD-Digital-Volt-Meter-Voltmeter-EU-Plug-Electric-Pen-Meters-UK/222535806720?hash=item33d02aef00:g:UiYAAOSwJH1ZNWya

 

I'm tempted to buy one myself for checking the voltage output of the inverter.

[chris]

Thanks robo. Might invest in one of those especially if heading to Spain for winter. Chris

[Noody]

Im pleased the Dometic fridge problems have raised their head again though my problem is the perennial 12 volt fridge operation not working.

 

Ive read and read until I hurt, no one seems to accept that a switching devise on the PCB is vulnerable and can't cope with 10 plus amps.

 

Im not buying another board, no way.

 

I have 12 volts from the Electroblock relay but it isn't getting past the switch on the PCB, this switch has to be a relay because of the high current ?

 

What Im going to do is fit a 20 amp rocker switch to the panel just under the electric step switch and complete the circuit to the 12 volt element there. The 12 volt element is ok.

 

What does Brian think, Brian used to have a Burster see. Oh, before I forget, who was it asserted the 12 supply to the fridge comes direct from the alternator ? Than 12 volts comes from a relay powered from the battery but only relays when the alternator is running.

 

Yes ?

[Brian Kirby]

Noody - 2017-11-04 9:15 AM...............................

1 Ive read and read until I hurt, no one seems to accept that a switching devise on the PCB is vulnerable and can't cope with 10 plus amps..........................

 

2 I have 12 volts from the Electroblock relay but it isn't getting past the switch on the PCB, this switch has to be a relay because of the high current ?

 

3 What Im going to do is fit a 20 amp rocker switch to the panel just under the electric step switch and complete the circuit to the 12 volt element there. The 12 volt element is ok.

 

4 What does Brian think, Brian used to have a Burster see.

 

5 Oh, before I forget, who was it asserted the 12 supply to the fridge comes direct from the alternator ? Than 12 volts comes from a relay powered from the battery but only relays when the alternator is running.

 

Yes ?

1 I guess that must be because if what you are implying were true, all fridges would be showing the fault you describe. It isn't, as you describe it, a common fault, so I'm led to suppose that either your diagnosis of the fault is incorrect, or your fridge PCB unusually has a defective component - but see 2 below.

 

2 But, have you verified that current is actually getting to the switch/relay on the PCB? Also, have you seen this string, and particularly "robinhood's" comments regarding a PCB mounted relay? http://tinyurl.com/yav5pwfh

 

3 That, as I understand it, seems to have the disadvantage that you'd have to remember to manually switch on the fridge each time you want it to run on 12V power, and off again each time you stop. It isn't clear which battery you'd take the fridge feed from, but either is liable to be flattened should you forget to turn off the 12V supply to the fridge element.

 

4 Indeed I did, in 2005, but only for just over a year, and it was our first van, so I was on a steep learning curve, and the van itself was faultless. I'm afraid I've no useful contribution to make based on that brief experience.

 

5 Most fridges have two sources of 12V power. The fridge controls are powered from the habitation battery, but the heating element is powered from the starter battery. There is, (usually :-)) somewhere, a relay which closes when the alternator begins generating current. When closed, this relay completes the circuit from the starter battery to the fridge 12V heating element. When the engine is stopped and the alternator ceases generating current, the relay opens to isolate the fridge heating element from the starter battery. This prevents the 12V fridge heater continually drawing current from the starter battery and so flattening it. It is this lack of automation in your proposed modification that creates the danger of a flat starter battery.

 

As to whether it is technically the alternator, or the battery, that actually provides the power to the fridge heating element I'll leave to others to argue! To me, it is the alternator, because a) it provides a higher voltage than the starter battery and b) the relay prevents the starter battery supplying the fridge when the alternator is not running. But, that is just my way of rationalising the working of the installation. :-)

[aandncaravan]

I agree with Brian or suspect your Fridge has been wired incorrectly at installation time or since?

 

The 12v for the element doesn't normally go anywhere near the PCB, but it's a while since I worked on a Dometic.

 

Also agree with Brian that the Element 12v power comes from the Alternator but routes via the Starter or Habitation batteries, Elektroblock, etc.

 

 

.

 

 

[Noody]

Thanks to both and I will reply shortly with a photo and my fridge model though I had assumed Brian would know. I'm not sure I can post a photo onto this forum.

 

Yes, the heavy duty 12 volts from the Electroblock come right to the pcb and are connected to spades either side of what appears to be a switching device. Maybe a small relay.

 

Everything up to that switching device is fine, when the engine is ticking over I get over 14 volts contrary to some opinions or rather other vehicles. When the engine is not running I don't get any supply.

 

Brian, the supply in this case comes from neither the habitation or engine batteries but from the EBL .

 

 

[Robinhood]

...I note Brian has name-checked me above.

 

I would counsel care before deciding what the 'norm' is re fridge wiring.

 

The fridge I've recently been diagnosing was part of a 'Tec Tower', and AES equipped. The main 12V feed for this went nowhere near the pcb, but directly to a 30A relay mounted on the back of the unit. The pcb only received separate low-current 12V for the control circuits, the output from which switched the above relay as the demand logically required.

 

Dometic (and indeed Thetford) practice may well vary by model (even if there is sound circuit-design logic for the above)

 

Likewise, wiring practice varies widely between converters (and between van models). Despite Brian's description, I've found fridges more often than not wired across the leisure battery. The provision of a D+ operated relay ensuring that it is indeed the alternator providing the current. (only when the engine is running, and effectively via the leisure battery charging circuit)

 

I know from experience that there are potential issues with this. Due to a blown fuse in the leisure battery charging circuit, I once arrived after a 4-hour journey with a dead leisure battery - the fridge was happily running in transit, (D+ present) but was depleting a battery that was not being concurrently charged.

[Brian Kirby]

Noody - 2017-11-04 2:50 PM.............................Brian, the supply in this case comes from neither the habitation or engine batteries but from the EBL .

I'm going to be a pedant and say I disagree! :-) The wiring may well come from the EBL, but the supply (i.e. the electricity) comes from the alternator via the starter battery.

 

I'm a mite wary about the component you have identified switching the 12V heater element. My understanding hitherto has been that the switching relay is not part of the fridge controls, but is sited elsewhere. I think this switching relay is within the EBL, and controls the supply of power to run the fridge and charge the habitation battery. There is no thermostatic control of the fridge when on 12V, the heater runs continuously for so long as the alternator is producing power.

 

What happens when the engine stops depends on whether the fridge energy sources are manually selected or automatically selected.

 

If energy selection is manual (MES), and 12V has been selected, the fridge will stop cooling until either gas or 230V is selected.

 

If energy selection is automatic (AES), as soon as the fridge loses 12V power it will look for 230Vpower, and if it doesn't "see" that source it will go for gas - and if it can't find gas it will get in a flap! :-)

 

The main problem seems to be that not all fridges are wired to Dometic's instructions, or are wired consistently even if from the same motorhome manufacturer. What I think we need to know is exactly which fridge you have in your van (i.e. RM????), and which Elektroblock EBL.

 

The following is on the assumption that your fridge is an RM7*** type, which seems likely for 2004 and, on an Elegance, I would imagine is AES.

 

The 12V circuits should terminate onto a connector strip at the top rear of the fridge, accessible through the upper air vent. There should be 6 connectors, of which, on an MES fridge 4 will be used, and on an AES fridge 5 will be used, with the sixth used if there is also a solar connection.

 

The terminals should be lettered A - D, D+ and S+.

 

A (-) and B (+) are for the heating element 12V power, and should have relatively chunky wires attached.

 

C (-) and D (+) are for 12V to the fridge controls (and the light, if fitted) and will have much lighter gauge wiring.

 

D+ and S+, if connected, will also have light gauge wires.

 

AFAIK, those should be the only 12V connections to the fridge.

 

You'll need to test for voltage at D, which should be a permanant live (from the habitation battery via the EBL), plus and B and probably D+, both of which should only be live (from the starter battery/alternator) when the engine is running.

 

If B is live with the engine running, the next test should be to fish up through the lower fridge vent to find the 12V heater element, and carefully feel if it is warm (careful, because it gets very hot after a while!).

 

If B is not live with the engine running then suspect the relay in the EBL.

 

If B is live but the heater element stays cold it suggests a failed heater element (or possibly that a connector has come loose at the element).

 

If D+ is live with the engine running the fridge is getting the signal to switch over to 12V power. If it is not, then there is a fault on the D+ feed from the EBL.

 

If you have power to both B and D+, but the 12V element doesn't heat, it suggests either the 12V heater element has failed as above, or a fault on the fridge PCB.

 

These tests should begin to pinpoint where the fault lies, but will not tell you exactly what it is that is at fault - for example whether wiring has been damaged, or whether a component, or which, has failed. But you should then know where to begin searching.

[Robinhood]

Brian,

 

I did say I'd counsel caution before making assumptions.

 

Some fridges are not thermostatically controlled on 12v, some are (and I believe many AES fridges fall into the latter category). Certainly, the 'Tec Tower' I referred to above is. I have had 'vans with both variants.

[Brian Kirby]

True, oh King! :-) But, the van is a 2004, which seems to put it in the era when the 12V was not thermostatically controlled and, since, as I understand Richard, his fridge functions normally on 230V and gas, I'm assuming that the thermostat is not likely to be relevant to his problem. What think you?

[Alanb]

My PVC dates from 2006 and has a Dometic RM 7361 fridge. I have to agree with Noody, that the 12V power for his fridge is controlled on the PCB.

 

Page 7 of the Dometic Instruction Book for RM 7xxx series fridges is headed "A. Manual Energy Selection". Section 5.2.2, sub section 1 describes 12V -operation (DC).

 

Section 2 of the above instructs use of the thermostat control to regulate the temperature. (In practice we rarely alter the setting.)

 

Further the Dometic wiring diagram on page 28 of the manual (Section 6 .9.6) clearly shows 12V +ve (B) routing in and out of the PCB via two blade connectors, as has been described.

 

As to diagnosing the relay as the root cause of the problem that is a different matter, as it could be the relay driver circuit rather than the relay.

 

If you discount solar input while the vehicle is in motion, the root source of 12V power is the alternator.

 

As has been observed there are various methods of getting 12V power to the fridge. I was interested to note Robin's comment in regard a faulty fuse in the leisure battery charging circuit. The CEB DS 520 in my PVC employed this system of a common connection to B1 +ve and hence the alternator.

I use the past tense because inconjunction with installing a CTEK D250S B2B charger, I have installed a new supply cable for the D250S and a separate fridge relay. (I did not want any of the modest 20A output of the D250S to be consumed by the fridge.)

 

Alan

 

 

[Noody]

Thanks to all of you for getting involved in this, when I read the posts this morning I was gratified and happy that between you, you know exactly what is going on. Even Brian who first asserted that the 12 volt element supply doesn't go anywhere near the PCB has now illustrated the exact wiring of my Dometic fridge.

 

I'm still in bed writing this and still have yet to find the model number, I will, soon. Yes it is manual selection.

 

The point I was trying to make with my proposed modification is that there is a history of failings with these fridges where the culprit has been the element switching at the PCB. Because everything else is working correctly and the selection was manual to start with why would I buy another PCB that would probably fail for the same reason, I'm going to suggest a reason for this failure.

 

If 12 volt supply is selected then you start the engine the driver circuit for the small relay would switch but only connect 12 V+ After the connection is made. If you first start the engine then select 12 volts that Dometic PCB relay has to connect 12 volts @ just over 10 amps, that relay doesn't look man enough for that current.

 

So, a 20 amp mechanical switch with a 15 amp fuse in a suitable position would switch the element circuit even if the load was present though in my view it would always be better to connect the 12 volt element conductors when no-load is present.

 

I have not spared any money keeping this van as the finest example of a 2004 Burstner Elegance but I refuse to contribute to failure in design and in workmanship so this wouldn't be the only modification I have made, in the event I sell the van I will add to the user manual any mods I made and the reason why.

 

I'm still trying to figure out how to attach a photo.

[Robinhood]

Brian Kirby - 2017-11-04 6:18 PM

 

What think you?

 

Brian,

 

You're asking me to do exactly what I've counsellors against.

 

Conjecture isn't helpful as there is so much variance.

 

I could give more-informed opinion with the fridge model number (as it is usually easy to check online). Alan has commented on thermostatic control of the 12v circuit - the RM7361 certainly does appear to have it, and my first experience was on a 'van bought new in 2005. It is also clear that the 12v feed does go to the cob on some fridges, the picture here clearly shows it (and I suspect the adjacent black box is the 12v relay - the 230v one is to the far right with stickers on it)

 

https://www.tinyurl.com/Fridgepcb

 

Commenting on the wiring to the fridge is considerably more challenging - there is so much variation. That on my current 'van. Is pretty conventional, via the EBL, but *is* fed from the leisure battery, not the vehicle one.

[Noody]

thank you Sir Robin. Yes, that is my fridge but I still have to find the model number. Where is it ?

 

Not that it matters now.

[Brian Kirby]

Alanb - 2017-11-04 8:58 PM

 

My PVC dates from 2006 and has a Dometic RM 7361 fridge. I have to agree with Noody, that the 12V power for his fridge is controlled on the PCB.

 

Page 7 of the Dometic Instruction Book for RM 7xxx series fridges is headed "A. Manual Energy Selection". Section 5.2.2, sub section 1 describes 12V -operation (DC).

 

Section 2 of the above instructs use of the thermostat control to regulate the temperature. (In practice we rarely alter the setting.)

 

Further the Dometic wiring diagram on page 28 of the manual (Section 6 .9.6) clearly shows 12V +ve (B) routing in and out of the PCB via two blade connectors, as has been described.............................Alan

Thanks for the correction Alan. I have that instruction book, and had always interpreted the wiring diagram as meaning the 12V connection by-passed the thermostat despite Dometic's description on page 7. However, as the fridge seems to work satisfactorily on other energy sources, it seems the thermostat is functioning as it should, so can probably be discounted as the source of Richard's problem.

[Brian Kirby]

Robinhood - 2017-11-05 9:07 AM

 

Brian Kirby - 2017-11-04 6:18 PM

 

What think you?

 

Brian,

 

You're asking me to do exactly what I've counsellors against.

 

Conjecture isn't helpful as there is so much variance.

 

I could give more-informed opinion with the fridge model number (as it is usually easy to check online). Alan has commented on thermostatic control of the 12v circuit - the RM7361 certainly does appear to have it, and my first experience was on a 'van bought new in 2005. It is also clear that the 12v feed does go to the cob on some fridges, the picture here clearly shows it (and I suspect the adjacent black box is the 12v relay - the 230v one is to the far right with stickers on it)

 

https://www.tinyurl.com/Fridgepcb

 

Commenting on the wiring to the fridge is considerably more challenging - there is so much variation. That on my current 'van. Is pretty conventional, via the EBL, but *is* fed from the leisure battery, not the vehicle one.

OK Robin (sorry, Your Maj :-)). So, what is the purpose of those relays? Are they just slaves to the thermostat output, necessary to maintain separation between the gas, 12V, and 230V control circuits, and to take their higher switching loads. If so, won't the failed relay in any case defeat Richard's proposed work around. Might he not do better to remove the PCB and then replace the errant relay - possibly - if space permits, with a higher rated one?

[Robinhood]

Apologies...the previous reply was rather mangled by spillchucker, posting quickly on mobile from my daughter's before leaving this morning.

 

I would surmise that the relays are there for slightly different reasons, though in fact perform the same end-purpose, which is to activate the 12V or 230V heater as and when all other conditions define that one or the other respectively should be on.

 

The control circuits (manual or automatic source switching, and thermostat where applicable) are all low amperage 12V circuitry, and the last logical step in the control circuit for either 12V or 230V use will be the appropriate relay.

 

The 12V relay is used to ensure that this low-current circuit can switch a separate much higher current circuit (the 12V heater) - conventional 12V relay use.

 

The 12V/230V relay is used to enable 12V-based control circuitry to switch a separate higher voltage 230V circuit (for the 230V heater), current here is much lower and less relevant.

 

I haven't read the detail of Richard's possible workaround yet, so won't comment here.

 

Certainly, if I was convinced that the 12V relay on the board was the issue (it would be fiddly, but shouldn't impossible to test), then I'd be looking for the relay part number, checking general availability and price, and considering the viability of replacing it on the existing board. A higher-rated relay *might* be an option, but you would be dependent on finding one that fitted the existing footprint and pin layout/geometry.

 

I would also not be looking at Dometic to supply a spare - the 12V/30A relay on the back of my friend's fridge can be bought as a Dometic spare for £30 upwards, or from a car electrics dealer for around £3 or even less!

 

I think people will be (for many, rightly) concerned at playing with a pcb, as any slip could easily introduce problems with other modes of operation. My recommendation to my friend arose since he uses the fridge on hook-up most of the time, it is without doubt the pcb 230V relay that is the issue, and the only really viable alternative is a £200 pcb replacement (plus fitting). An attempt to fix for around a fiver seems worth the money and effort, even if the replacement is subsequently required.

 

(TBH, it wouldn't be entirely impossible to remove the 12V heater feed from the PCB, reposition it to the back of the fridge, and run control wiring from the pcb to a conventional 12V/30A car relay fixed to the back of the fridge (which is exactly as it is on the Tec Tower) - it'd still mean jumping the low-current switching wire(s) off the pcb, though, and would be mildly "inelegant".)

[Alanb]

The 12V and 230V relays will be operated by the energy selection, and subject to the thernostat control.

 

Again I agree with Noody that the black object in the middle of the picture is the 12V element control relay, the rating of which he has reservations about.

 

If Noody perhaps with the aid of a magnifying glass, can obtain a makers name and part numper he may well be able to download a spec sheet via an internet search, and perhaps a replacement relay if necessary.

 

The 12V heating element is a resistive load and will not have the large initial inrush current of a filament lamp of simiar wattage.

 

By way of illustration was for a long time sceptical of the rating of several of the relays in the CBE DS520 on my PVC. I would have guessed that they are about 15mm cube in size. One of them controlled the fridge 12V element power.

 

After researching as I suggest above I was able to download a makers spec sheet. In fact the relays 12 x 12.9 x 10mm in size. The max current rating is 30A for a resistive load at 23C, and downrated to 25A at 85C. Endurance with a reistive load is quoted as 300,000 operations. I suspect that the relay on the Dometic PCB is similar.

 

My reccommendation would be to repair the pcb if possible. This will retain the thermostatic control.

If Noody still has reservations as to the relay rating, why not install a secondary slave relay close to the fridge (as also suggested by Robin). I have used "Automotive Micro Relay" with holder for several applications including my new fridge relay.

 

Alan

[Noody]

These varied comments are very positive for me, and helpful. I'm still committed to my proposed simple work-around. The Dometic control was manual, I will have a manual control with an LED LIGHT.

 

I took the pcb out for a looksee on the basis of Alan's recommendation. I couldn't replace that failed switch and it may not be the switch, maybe another component. Either way as I keep saying there is a lot of history attached to this failure.

 

If I had an electronics workshop within driving distance I might consider a repair, I won't consider a replacement Dometic pcb and it's not just the money. I live in rural north Pembrokeshire, the benefits of lining where I live are huge but there is a price to pay. When my Truma boiler needed help it was a three day trip to Derbyshire.

 

I have just completed a test rig for my workaround, it works perfectly. The Dometic is in my workshop connected up to gas, 240 volts, 12 volts low current supply and 12 volts high current supply from its own battery source supported by a charger. I was surprised how quickly the 12 volt element heated up. I'm even getting my head around temperature control in the case I need it.

 

Those Dometic fridges are a thousand pounds, I expect more even though my van is 13 years old because this problem emerged around 2006 on the various forums.

 

Going back to my work-around, how many of us drive without a stop for more than four hours, even if it's just for a pee. I just cannot see a problem with the work-aroun but I am inviting comments.

[Alanb]

My curiosity has been aroused, and it is many years since the last time that into a fridges control panel,so may I ask some questions please.

 

How is the fridge control panel secured? I can assume that the control knobe pull off, but what next to reveal the PCB? Can this be done without partially removing the fridge from its housing?

 

Thanks

 

Alan