You are logged in as a guest. 
  Home Forums Home  Search our Forums Search our Forums    Log in to the Forums Log in to the Forums  register Register on the Forums  

 Forums ->  Motorhomes -> Motorhome Matters
Jump to page : First 1 Last
Format:  Go
Dometic AES fridge won't switch to gas
AuthorMessage
usernicaf
Posted: 10 January 2022 12:11 PM
Subject: Dometic AES fridge won't switch to gas
 
Just joined

Posts: 3



I have a 2007 Adria Coral SP650 fitted with a Dometic AES RM fridge. Electrics are controlled with a Schaudt EBL225 which has a 10A removable fuse slot specifically for an AES fridge. The fuse is in place. All 3 functions work when selected. However when set to 'auto' the fridge will not switch by itself from 12v (auto selected when the engine is started) to gas, with the consequence the fridge is running on the leisure battery (this can be evidenced by the Schaudt control panel which shows a reduction in its charge status). Given the amperage of the fridge (c. 8-10A) this will rapidly drain the battery! In my previous motorhome, which had a similar set up, the when set to auto the fridge would effectively go off when the engine was stopped and wait c.15 minutes before lighting the gas. The fridge required no intervention. Somehow the fridge is not switching by itself. What controls this? - the fridge PCB, a relay in the fridge or the EBL? Has anyone any ideas?
userbuddy
Posted: 10 January 2022 1:07 PM
Subject: RE: Dometic AES fridge won't switch to gas
 
Keeps coming back for more

Posts: 174
1002525
Location: West Sussex Autocruise Rhythm 2015


If you leave the AES fuse out of the EBL I think you should find that the fridge will work as a normal 3 x way without involving the leisure battery (as a heat source) and hopefully go to gas when parked up.(as long as gas supply is ok)
As I understand it , the leisure battery use feature is normally to keep the fridge cooling for ferry crossings etc (when the gas has to be turned off)

Edited by buddy 2022-01-10 1:28 PM
userRobinhood
Posted: 10 January 2022 1:24 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


If the AES fuse is present, the 'fridge will work on the leisure battery(ies) if switched manually to 12 volt.

In addition, I'm pretty sure that on auto the presence of this fuse "bridges", from the leisure batteries, the safety interval between ignition off and gas ignition.

Certainly, my brief test just now left the 'fridge running on battery when the ignition was turned off (and I haven't had any noticeable issue with it switching to gas after the expiry of the interval).

I'd leave the AES fuse in, run with engine on, then ignition off and let the "15 minute" interval expire. (under most circumstances, after any significant on-road use, being thermostatically controlled the probability of the cooler immediately switching in is low, and the consumption for 15 minutes is substantial). I suspect it will continue to run on battery, but switch to gas after expiration of the safety interval.
userDerek Uzzell
Posted: 10 January 2022 1:28 PM
Subject: RE: Dometic AES fridge won't switch to gas
 
50005000500050001000100100252525


This 2013 forum thread may be of interest as it discussed 'smart' fridges, EBL units and the fuse mentioned here.

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/EBL-AES-fridge-fuse/33352/
userBrian Kirby
Posted: 10 January 2022 6:59 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


50005000500020002000500100100
Location: East Sussex. Motorhome: Knaus Boxstar 600 Street


An AES fridge prioritises its energy sources in a fixed order. It looks first for a 12V supply, and if no 12 V is available it looks for a 230V supply, and if no 230V, it looks for gas.

It should never be able to draw 12V cooling power from the leisure battery. The 12V power supply is supplied via a relay that is only energised when the engine is running and the alternator generating current. The same relay (or possibly a separate relay working in parallel) also controls the charging current to the habitation battery from the alternator. If the alternator is not generating current the relay/s open to isolate the starter battery from the habitation battery (to prevent habitation loads flattening the starter battery) and so prevents the AES fridge continuing to run on 12V power from the habitation battery.

So, having lost its default 12V supply, it goes to priority 2, and if no 230V supply is available, after a delay of approximately 15 minutes (the filling station forecourt safety delay) it switches to gas. Once this 15 minute period has passed, it will try to ignite the gas. Then, if no gas is available, it will enter fault mode and the fridge control panel will show a fault code or message. It seems your fridge is not doing this, as you haven't mentioned any code/message on the fridge panel.

There is permanent a 12V supply to the fridge to power the controls. From memory this supply is usually fused at around 3A. If that supply were absent the fridge would not function and the control panel (and the controls) would be dead.

You say "............when set to 'auto' the fridge will not switch by itself from 12v (auto selected when the engine is started) to gas, with the consequence the fridge is running on the leisure battery (this can be evidenced by the Schaudt control panel which shows a reduction in its charge status). So the automatic function is working to select the 12V supply once the alternator is delivering current, but sticks in 12V mode after the engine is stopped and the alternator supply ceases.

You refer above to the Schaudt control panel showing "a reduction in its charge status". But, unless you are on EHU, when the alternator ceases delivering current there will be no charge available to (presumably) the leisure battery. Are you sure that what you are seeing is just the control panel recording the normal reduction between the output voltage of the alternator, and the charge state of the habitation battery - which will always be lower?

Also, what does the fridge control panel show when the engine/alternator are stopped and no 230V is available? There is usually an indication on the panel of which source the fridge has selected. Could it be that what you are seeing is simply the fridge, having recorded that it has been receiving power from the alternator but that power supply is no longer available, and that no 1230V supply is present, simply "thinking" that it is at a filling station and waiting its allotted time before trying to ignite the gas.

Silliest question last, do you have gas in your tank/cylinder, is the supply cock on the cylinder or tank "on", is the (presumed) rupture control valve in the flexible high pressure hose open, and is the gas cock for the fridge open?
userKeithl
Posted: 10 January 2022 7:31 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


Lord of the posts

Posts: 6040
5000100025
Location: Birmingham. 2004 Auto-Trail Cheyenne Mercedes 313.


Is the fuse mentioned for an AES fridge or a compressor fridge?

Have you got the manual for the Schaudt control panel and if so what mention is made of that specific fuse?

Have you tried pulling the fuse and seeing how the AES fridge performs?

Keith.
userRobinhood
Posted: 10 January 2022 8:15 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


Brian Kirby - 2022-01-10 6:59 PM

It should never be able to draw 12V cooling power from the leisure battery. The 12V power supply is supplied via a relay that is only energised when the engine is running and the alternator generating current. The same relay (or possibly a separate relay working in parallel) also controls the charging current to the habitation battery from the alternator. If the alternator is not generating current the relay/s open to isolate the starter battery from the habitation battery (to prevent habitation loads flattening the starter battery) and so prevents the AES fridge continuing to run on 12V power from the habitation battery.



Brian,

in the case of an AES fridge wired as such in conjunction with a Schaudt Electroblock with an AES fuse fitted, this isn't true.

The fitting of that fuse enables a separate non-engine dependent 12V supply to the fridge cooling circuit which, as per my post above, has some "interesting" effects.

"This relay supplies the AES/compressor refrigerator with power from the starter battery when the vehicle engine is running and the D+ connection is live. An AES refrigerator is powered by the living area battery when the vehicle engine is not running."

(For AES you can also substitute 'compressor' where one is used (and you should be used to that arrangement from your 'van ), the Electroblock provides separate arrangements and wiring outlets for non-AES fridges which do not use the leisure batteries once the engine is off)

Most notable of the effects is that manually switching the fridge to 12v will enable it to run from the leisure battery(ies) regardless of the engine running or not.

Using "auto" mode, the 'fridge runs from 12v when the engine is on, but switches to gas, after the safety interval, when the engine is turned off (and if gas is not available, it will go into failure mode, not revert to battery in auto mode).

Following the OP, it occurred to me that, though I had never noticed it, with the AES fuse fitted and in auto mode the safety window before gas lighting might well be 'bridged' using the batteries. I've always left it to get on with things, and the gas has always lit at the appropriate interval, but I've never checked the indicator lights (obscured by the closed door on my 'fridge) in the interim period.

So, today, I started the engine, set the fridge on in auto mode (it selected 12v), and then turned the engine off. The 12v indicator light, and all other relevant indicators, remained illuminated (which is in contradiction to the manual, which says that, at this point the temperature display lights will go out, indicating it is in standby). After the requisite 15 minutes, the fridge switched to gas, the 12v indicator was extinguished only at that point, and the gas indicator was illuminated.

Whilst the display in that interval contradicted the manual, I can't find evidence that the leisure battery(ies) were actually in use whilst the 12v indicator was lit until the gas kicked in. I suspect, from seeing the voltage drop when I subsequently manually switched to the batteries that it wasn't, but it isn't conclusive (though probably consistent with the AES switching logic).

It may be that the OP has a problem, but if the fridge is simply indicating itself still running off 12v once the engine is switched off, if it is paralleling my experience, it might still switch to gas after the "safety" interval.

(Behaviour of AES fridges using Schaudt equipment varies by installation; It is quite possible to wire via the "non-AES" connections, whereby the fridge won't be manually switchable to a 12v leisure battery supply when the engine is off)
userRobinhood
Posted: 10 January 2022 8:25 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


Keithl - 2022-01-10 7:31 PM

Is the fuse mentioned for an AES fridge or a compressor fridge?

Have you got the manual for the Schaudt control panel and if so what mention is made of that specific fuse?

Have you tried pulling the fuse and seeing how the AES fridge performs?

Keith.


The EBLs generally specify one wiring outlet for AES/Compressor, and a different one for non-AES fridges.

The AES fuse protects the wiring back to the leisure batteries which may be in use in certain circumstances for an AES fridge when the engine is off, and always for a compressor fridge in that state. For an AES fridge, it is not critical (for a compressor, it is)

Assuming the fridge is wired to the AES outlet, pulling the AES fuse should inhibit the use of the leisure batteries in all circumstances that would otherwise enable them (with engine off), but still provide 12v from the engine when running (much like wiring to the non-AES outlet). If the fridge is actually wired to the non-AES outlet, then it will make no difference at all.

Edited to add

I think my testing above had an omission, and that it is more likely the leisure batteries are bridging the safety interval, as I think I had the fuse out when I checked voltages.

I think the AES logic leaves the fridge on 12v for 15 minutes, but a conventional wiring would simply have isolated the 12v supply from the engine in the interim, so it can leave as is before eventually switching to gas.

More tomorrow

Edited by Robinhood 2022-01-10 8:48 PM
userBrian Kirby
Posted: 11 January 2022 6:43 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


50005000500020002000500100100
Location: East Sussex. Motorhome: Knaus Boxstar 600 Street


Robinhood - 2022-01-10 8:15 PM
Brian Kirby - 2022-01-10 6:59 PM
It should never be able to draw 12V cooling power from the leisure battery. The 12V power supply is supplied via a relay that is only energised when the engine is running and the alternator generating current. The same relay (or possibly a separate relay working in parallel) also controls the charging current to the habitation battery from the alternator. If the alternator is not generating current the relay/s open to isolate the starter battery from the habitation battery (to prevent habitation loads flattening the starter battery) and so prevents the AES fridge continuing to run on 12V power from the habitation battery.

Brian,
1 in the case of an AES fridge wired as such in conjunction with a Schaudt Electroblock with an AES fuse fitted, this isn't true. The fitting of that fuse enables a separate non-engine dependent 12V supply to the fridge cooling circuit which, as per my post above, has some "interesting" effects.

"This relay supplies the AES/compressor refrigerator with power from the starter battery when the vehicle engine is running and the D+ connection is live. An AES refrigerator is powered by the living area battery when the vehicle engine is not running."

2 (For AES you can also substitute 'compressor' where one is used (and you should be used to that arrangement from your 'van ), the Electroblock provides separate arrangements and wiring outlets for non-AES fridges which do not use the leisure batteries once the engine is off) Most notable of the effects is that manually switching the fridge to 12v will enable it to run from the leisure battery(ies) regardless of the engine running or not.
3 Using "auto" mode, the 'fridge runs from 12v when the engine is on, but switches to gas, after the safety interval, when the engine is turned off (and if gas is not available, it will go into failure mode, not revert to battery in auto mode).
4 Following the OP, it occurred to me that, though I had never noticed it, with the AES fuse fitted and in auto mode the safety window before gas lighting might well be 'bridged' using the batteries. I've always left it to get on with things, and the gas has always lit at the appropriate interval, but I've never checked the indicator lights (obscured by the closed door on my 'fridge) in the interim period.
5 So, today, I started the engine, set the fridge on in auto mode (it selected 12v), and then turned the engine off. The 12v indicator light, and all other relevant indicators, remained illuminated (which is in contradiction to the manual, which says that, at this point the temperature display lights will go out, indicating it is in standby). After the requisite 15 minutes, the fridge switched to gas, the 12v indicator was extinguished only at that point, and the gas indicator was illuminated.
6 Whilst the display in that interval contradicted the manual, I can't find evidence that the leisure battery(ies) were actually in use whilst the 12v indicator was lit until the gas kicked in. I suspect, from seeing the voltage drop when I subsequently manually switched to the batteries that it wasn't, but it isn't conclusive (though probably consistent with the AES switching logic).
7 It may be that the OP has a problem, but if the fridge is simply indicating itself still running off 12v once the engine is switched off, if it is paralleling my experience, it might still switch to gas after the "safety" interval.
(Behaviour of AES fridges using Schaudt equipment varies by installation; It is quite possible to wire via the "non-AES" connections, whereby the fridge won't be manually switchable to a 12v leisure battery supply when the engine is off)

Hi Bob - I've numbered your post to clarify which parts I'm responding to.

1 I'm not that familiar with Schaudt wiring practice, as I've only had two vans with Schaudt gear. A 2005 Burstner that had an MES fridge, which gave no trouble at all during the time we owned it, so I never had to explore which was wired to what, or how! My other Schaudt experience (Hymer Exsis-i) was similar in terms of functional reliability, but the fridge was an AES Thetford, which although similar to Dometic AES, I believe is not exactly the same. However, I had always understood that neither the starter battery nor the habitation battery should power the fridge when the alternator is not generating current, as the fridge cooling load would relatively quickly flatten either. So, the fail safe is to automatically disconnect the cooling supply when the alternator is not generating - in case the owner might forget to do so and find one or other of the batteries unexpectedly flat.

2 On the subject of compressor fridges, our present van was supplied via CBE electrics and, as standard, a compressor fridge - but with a (very!) manual three way fridge as an option. Ours has the three way option fridge and, a year or so after we got it I became aware that if the 12V supply was not de-selected in favour of gas or mains, the fridge happily continued drawing 12V power even when on EHU. Fortunately our other 12V demands are fairly light, and the 230V CBE transformer/charger had sufficient output to meet the charging demands from both batteries and run the fridge. Mind, its cooling fan was running continually - and it was fairly warm - which is what drew my attention to it, and to the energy selector still being on 12V! So, fridge swiftly switched to 230V!

But, I was puzzled as to why this was possible as the manual said it shouldn't be. The van was due a warranty damp check shortly after our return so I mentioned my experience to Southdowns when booking the check, and they said they'd get a tech to investigate when it went in. It took him all of 5 minutes to sort - by pulling the A£S/compressor fridge 12V feed (just a wire link) in the CBE DS300 distribution box, which I gathered from the grin on his face was not the first one he'd met! The link is in place by CBE by default, but should have been pulled when the optional three way fridge was installed.

3/4 This tempts me to wonder if that AES fuse should be pulled with an AES fridge, and should only be inserted when a compressor fridge is specified. A three way fridge should always have one of two other sources of energy available and, if an AES model, will, as you say, go to fault mode if neither is present. In that way the forgetful owner is protected from at least one flat battery, which seems reasonably logical to me. It also seems to reflect what I remember of the way the Thetford fridge in the Exsis worked. I once forgot to turn off the fridge when on the shuttle and, by the time we'd got to the other side the fridge was in full panic mode and wouldn't function at all until it was turned off to re-set it. Then, it just worked normally.

5 No comment.

6 But might the display have been as the manual with the "AES" fuse pulled?

7 As you say, there may be a control fault, but perhaps it might be worth the OP trying again with the Fuse pulled - to see if his 2007 Adria Coral with Dometic AES fridge and Schaudt electrics reflects your experience above. It might (although tedious!) be worth doing so and noting and timing the exact sequence of events as the fridge switches between its various possible energy sources, with the fuse both inserted and pulled. If it emerges that there is a fault, at least the record of what happens under both conditions may assist in identifying its cause.
userRobinhood
Posted: 11 January 2022 8:10 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


Brian,

Sorry, this is a bit long-winded.

The logic behind Schaudt (and Hymer) thinking largely (but see below) escapes me, but I can assure you that an AES fridge, connected to the AES EBL outlet, and with the AES fuse inserted, will (under certain circumstances) run off the leisure battery(ies). (I've only definitely seen it on mine with manual switching to 12V mode with the engine off, but the resulting voltage drop shown at the panel makes it very apparent).

Perusal of the EBL circuit diagram makes this obvious, logical and easy to understand. My EBL (and others with the AES fuse) contain two separate and alternate outputs for fridges; one for AES/Compressor, and one for Absorption fridges.

These are controlled by different, separate internal relays in the EBL, only one relevant on any installation depending on which output the fridge has been wired to.

The Absorption relay and output is normally open-circuit (i.e. unpowered), but connects to the starter battery on the D+ signal generated with the engine running.

The AES/Compressor relay and output is normally connected to the leisure battery(ies), but connects to the starter battery on the D+ signal generated with the engine running. Hence the extract from the Schaudt manual I posted above, viz: "This relay supplies the AES/compressor refrigerator with power from the starter battery when the vehicle engine is running and the D+ connection is live. An AES refrigerator is powered by the living area battery when the vehicle engine is not running."

In both cases, the running from the starter battery is protected by a (20A) fuse mounted externally to the EBL. When running from the leisure battery(ies) on the AES/Compressor circuit, this is protected by the (20A) AES fuse in the EBL.

Removal of the AES fuse (and the fuse position is clearly marked AES/Compressor, not just Compressor) makes the AES/Compressor circuit equivalent to the the absorption one in function (i.e. there is no 12v supply when a D+ signal is not present). Patently, this wouldn't be sensible for a Compressor fridge which is required to run off 12v whilst stationary, but it wouldn't be entirely fatal for an AES one.

Remember, for an AES fridge, the cooling source in action at any one time is largely decided by the fridge control electronics anyway, which use the same D+ signal in its logic to determine the availability of 12V (via the starter battery at least), and chooses from a hierarchy of available sources.

The above thus makes it interesting to cogitate why the connections weren't simply "Compressor" and "Absorption" (including AES). one assumes there is at least some reason for not simply using the Absorption circuit for AES fridges.

So, it makes it possible to run the AES fridge off the leisure batteries - possibly useful for very short term if set manually, but I suspect this facility is really there to work with AES fridges in auto mode and with an S+ (solar) fridge input signal, which switches in 12v when solar is being triggered (and that 12v supply would be via the leisure battery(ies) connection).

Anyhow, when checking the functionality of mine (after the OP) I noted that running on "auto" with the engine running, selected and indicated the 12v option as expected, and that subsequently turning off the engine made no difference to any indication (i.e. all the lights remained the same, and 12v was still indicated) until the 15 minute safety interval had expired, at which point it switched to, and indicated, gas operation. I was conjecturing whether, during this interim period, as the 12v would now nominally be available from the leisure battery(ies), the auto-logic was "bridging the gap" using this. It would be another plus for the AES-type connection, but I couldn't see a voltage drop at that point. (If I had, it would align to some extent with the OP).

So, I would postulate that the AES connection and fuse are definitely required for:
- a compressor fridge;
- an AES fridge if you are using solar and the S+ signal (rare, I should think);
- if you (manually) want to briefly run your fridge from 12v with the engine off (I've a 190Ah battery capacity, so could be useful for short sea crossings);
......and the jury is out on whether it bridges the safety interval before gas ignition (though my feeling is now not).

If none of the above applies, I'm pretty sure that removal of the AES fuse for a fridge connected to the AES outlet will have no negative effect (the D+ controlled engine 12v supply comes down the opposite side of the associated relay), unless it is, in fact, bridging the safety interval (and removal of that function would be less-than-critical).
usernicaf
Posted: 12 January 2022 9:42 AM
Subject: RE: Dometic AES fridge won't switch to gas
 
Just joined

Posts: 3



Hi Brian and thank you for taking the time to reply.

To clarify - with the fridge set to Auto and the engine running the fridge control panel shows two green lights, 12v and Auto setting. When the engine is stopped the same two lights remain on. They will remain on all the time and are drawing from the leisure battery as evidenced by the status of the residual charge in the leisure battery (as shown on the control panel - I clearly didn't express it clearly stating "a reduction in charge status".) with the result that if left overnight for example the leisure battery will be completely discharged. No matter how long you leave it the fridge will not switch to gas!

To answer your further question yes the gas is on.

As stated in my original post all 3 functions work satisfactorily - my problem is with the inability of the fridge to switch to gas automatically away from 12v and to avoid discharge of the leisure battery. Obviously I can manually select gas when I stop the engine but that defeats the object of an AES fridge.

Does this give you any clues as to where the fault may lie? I really appreciate your input as I have seen many posts from you and value your obvious expertise.

Regards Nick
userBrian Kirby
Posted: 12 January 2022 11:34 AM
Subject: RE: Dometic AES fridge won't switch to gas
 


50005000500020002000500100100
Location: East Sussex. Motorhome: Knaus Boxstar 600 Street


Thanks Nick

From what you say, turning the fridge off re-sets its auto mode "memory" - so that the cycle of fridge on, select auto, start engine, fridge switches to 12V power, stop engine, fridge remains "stuck on 12V power, can be repeated more or less endlessly.

That seems to me to suggest that the relay that switches in the 12V power is "sticky", and is not opening as it should to isolate the 12V source when the engine is stopped. I don't think the fault can be with the fridge controls, as the relay is the only source of 12V power to cool the fridge so, if the power has gone, I can't visualise where the fridge can be finding its 12V supply. If the 12V supply remains live with the engine stopped, the fridge has no way to "know" that it isn't supposed to be using 12V and start looking for an alternative energy source.

But expertise? Nah, I would never claim expertise, especially regarding Dometic AES fridges or Schaudt electrics. As I said above, I've had two vans with Schaudt electrics, neither involved any problem hunting, and only one had an AES fridge - and that was by Thetford, not Dometic! So, some expert! ;-)

However, I would be inclined to test whether the 12V supply to the fridge remains live when the fridge is in auto mode, has selected 12V power with the engine running, and remains in that mode when the engine is subsequently stopped.

If you can locate the relay, the simplest test would probably be to use a multi-meter between the relay terminals and earth, with the engine running and the fridge set to auto/12V to verify that power is available, and then stop the engine and re-test whether the 12V supply remains live. If the relay is not accessible, I think you'd instead have to locate the 12V terminals on the rear of the fridge (probably not easy) and proceed as above, with the meter between the +12V fridge terminal, and then stop the engine to see if the 12V supply dies as it should.

That, I think, will require two people, one in the driving seat and the other by the relay/fridge to observe what happens with engine running/not running.

Quite how you then proceed to clear the fault will depend on where the relay is (for example whether, as Robinhood suggests above, the relay is in the EBL, or is external to the EBL. If external, it should be no more complicated than swapping in a new relay - and quite cheap into the bargain. But if the relay is in the EBL, I suspect the EBL would have to go for repair, or a way to by-pass the EBL relay and substitute an external one, found.

But that's just me! Someone with knowledge of EBLs and Dometic AES fridges may well disagree with the above (very!) non-expert diagnosis! :-|

Edited by Brian Kirby 2022-01-12 11:39 AM
userbuddy
Posted: 12 January 2022 1:00 PM
Subject: RE: Dometic AES fridge won't switch to gas
 
Keeps coming back for more

Posts: 174
1002525
Location: West Sussex Autocruise Rhythm 2015


Have you tried it with the AES fuse removed as that fuse is not always fitted even when a AES fridge is fitted. (depending how it is wired in)
userCasimir
Posted: 12 January 2022 3:49 PM
Subject: RE: Dometic AES fridge won't switch to gas
 
Liking what I've found

Posts: 52
2525
Location: UK & Spain - 2007 Fleurette 73LJ 3.0L LHD


My experience with my Dometic RM7655L fridge whilst not the same, might be of interest.

I had been having problems with the fridge for several months. Sometimes the gas burner would fire up and sometimes not. There did not seem to be any pattern to the problem. The burner control box had been replaced in addition to the gas burner itself but it still would only fire up intermittently. To cut a very long story short, purely by chance I found a poor connection in the burner control wiring loom. I replaced that and have not had any problems since then.




(05885.jpg)



Attachments
----------------
Attachments 05885.jpg (20KB - 10 downloads)
userRobinhood
Posted: 12 January 2022 6:00 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


Nick,

can you post the model of your 'fridge, as different vintages of AES ones have slightly different 12v functionality, and there might be different things to check (or different orders).

At first glance, I can't see that Brian is taking you in the correct direction. The availability of a 12v heating supply isn't what drives the logic for the power source, essentially, it is the 'fridge control electronics that make the decision as follows (in that order of precedence):

i) Is there mains power at the control electronics?; if so, select 230v

ii) is there a D+ or S+ signal available at the control electronics? ; if so, select 12v (and the EBL wired to the AES outlet with the AES fuse connects the starter battery if there is D+, and the leisure battery if there isn't - but note, the 'fridge will not use the available 12v supply from either battery unless the control electronics see a D+ or S+. Wired through the AES leg of the EBL. there is always a 12v supply available but it is only selected via the D+/S+ signal)).

iii) if i) or ii) do not apply, use gas.

I can look a bit closer at the possibilities if I know the fridge model, but....

...for me, without further info the prime suspect is that the fridge electronics are faulty, and it is functioning as if there is a permanent D+ (or S+) signal. This would inhibit switching to gas, and run off the starter battery whilst mobile, and the leisure battery when stationary (the switch between these achieved by the EBL seeing/not seeing the separately supplied D+ signal from a running engine).

If this is so, then removing the AES fuse would prevent the leisure batteries being used when stationary, but wouldn't enable gas operation in auto mode.

If the above is correct, then I would suspect that plugging, with engine off, into the mains and selecting auto would cause the fridge to run on 230v. Subsequently removing the mains supply, still stationary, would normally cause the fridge to fall back to gas, but with my hypothesis, it would fall back to 12v from the leisure batteries. I'd have to check what happens on mine with mains on and the engine running (i.e. mains and D+ at the same time).

Edited by Robinhood 2022-01-12 6:18 PM
userDerek Uzzell
Posted: 12 January 2022 6:44 PM
Subject: RE: Dometic AES fridge won't switch to gas
 
50005000500050001000100100252525


In this 2020 MHFacts discussion Nick mentioned that his Adria's fridge was a Dometic RM 7655 .

https://forums.motorhomefacts.com/182-electrical/238389-adria-coral-fridge-not-working-12-volt.html

There's an operating/installation manual here

https://www.manualslib.com/products/Dometic-Rm-7655-L-9789624.html
userRobinhood
Posted: 12 January 2022 7:40 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


...the RM7655 (or at least the models I've seen) have a separate, conventional 12V relay mounted and accessible on the rear of the fridge body (something absent from later AES fridges, where I think the function must be in the control board from diagrams) and this controls the 12v "heater" circuit. It is switched by the logic of the electronic control board.

Patently, this must be at least, "closed" on auto on Nick's fridge (as it is functioning on 12V) but I note that the relay shares a wire (the ground for the 12v supply) with the burner control device.

I can't, from the circuit diagram, deduce any issue here that would cause the described problems, but I'd certainly be looking at the relay to see if it had stuck closed, since this would use 12v power all the time (assuming the AES fuse was in place). Unless the shared wire or a fault therein has some effect on the burner control, however, it wouldn't account for not lighting on gas.



(RM7655_circuits.jpg)



Attachments
----------------
Attachments RM7655_circuits.jpg (97KB - 11 downloads)
userKeithl
Posted: 12 January 2022 7:51 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


Lord of the posts

Posts: 6040
5000100025
Location: Birmingham. 2004 Auto-Trail Cheyenne Mercedes 313.


Nick,

Have you tested the voltage at the fridge's D+ terminal with a multimeter or test light to see if the logic from the EBL is correct? ie Is the output from the EBL the cause of the problem?

Keith.
userRobinhood
Posted: 12 January 2022 8:58 PM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


Keith,

As above, a permanent D+ (or the very unlikely S+) i.e. still present without the engine running could cause the symptoms. It is clear however that the EBL is sensing the lack of a D+ when stationary, as the leisure batteries are being brought into circuit.

I think the D+ is simply a passthru in the EBL so it's worth a test but, I think, an unlikely issue, as the lack of a D+ to proper working electronic controls would never invoke 12v running.

Certainly the lack of a D+ signal at either the EBL or the fridge controls (or both) would cause problems, but I can't logically align this occurrence at either or both with the described symptoms.

Problems with the control electronics on this fridge are not uncommon. I ran a thread on here about 3 years ago about me diagnosing a stuck 12/230V relay on one which left 230v active under all circumstances (even when switched off!). If the controls are stuck with a permanent D+ (or a relay which reacts to such), then the symptoms match.

But....It is all conjecture and probabilities. Applying logic can change the probabilities but I wouldn't entirely ignore even the low ones, especially as the control electronics are expensive.
userRobinhood
Posted: 13 January 2022 8:47 AM
Subject: RE: Dometic AES fridge won't switch to gas
 


5000
Location: Sherwood Forest


..just as an aside, I've checked the EBL225 circuit diagram, and (unlike many EBLs, including my EBL30) it has only a single fridge circuit and relay.

It is, however, functionally equivalent to using the "AES" circuit provision on those EBLs which have two (it uses the starter battery when a D+ is present, and the leisure batteries when it isn't (and the latter is inhibited by removing/not fitting the AES fuse).

Frankly, I find that arrangement rather more logical than the provision of two alternate circuits, but as it is functionally equivalent it makes no difference to the views in the posts above.
usernicaf
Posted: 18 January 2022 8:41 AM
Subject: RE: Dometic AES fridge won't switch to gas
 
Just joined

Posts: 3



Thanks for your very details email and I will look at the various issues raised. The fridge is indeed the RM7655. There is a few things to check but as it below zero degrees here in the SW of France where I live, I will defer doing the checks until it warms up a bit! I promise I will reply to your, all other points when I have got some feedback

Regards to all

Nick
Jump to page : First 1 Last
Printer friendly version
E-mail a link to this thread
Jump to forum :


(Delete all cookies set by this site)(Return to Homepage)

Any problems? Contact the administrator