Funny (worrying) 12v system fault

[Cliffy]

Travelled home from Dover yesterday 310 miles in the pouring rain (Ugh).

This morning when I turned on the ignition a rattling noise came from a contactor somewhere in the Dometic fridge and continued after I switched the ignition off.

When  I switched the fridge to off, gas, or 230 volts it stopped rattling but the MH control panel displays 'Engine is running system is diabled'. Switching back to 12 volt this message clears and fridge contactor stops rattling (sometimes).

Anyone got any experience of a similar problem. It could be a fault with the fridge causing it or a fault somewhere else in the system that could be causing the fault in the fridge and the control panel.

With the engine running everything works as it should and with a bit of playing around with the fridge switch and setting it on 12 volts all works OK on the panel.

I have booked it in to have it repaired but the earlist they can look at it is next Wednesday and I don't like paying for repairs that could possibly do myself with a little guidance from the good people on this forum..

[Tracker]

I would suspect low voltage caused by either an iffy battery or more likely a bad connection somewhere - probably a fuse or fuse holder.

 

If you have a digital volt meter check the voltages at various places as you check the fuses and connections and see what you come up with.

[casey]

Hi Cliffy,

May not help your case, but we have a 2006 Autotrail Dakota with the electrics thingy !! above the door.

While travelling through france earlier this year there was this clicking sound coming from the thingy !!

It said " engine running system disabled " though engine wasn`t running.

Out of desperation and on suggestion of bil i disconnected the thingy and connected it again, it reset itself and have had no probs since ( touch wood )

casey.

ps sorry about the thingy thing but having a senior moment & cannot remember it`s name !!!!!!

[Tracker]

I think Casey means the display and 12 v control panel and yes, if it is a Sargent system, getting behind it, unplugging, leaving for a few seconds and replugging can indeed often reset the system when you get unusual symptoms.

[Derek Uzzell]

Cliffy

 

The 12V electrical systems of UK-built motorhomes will normally include two relays (the component you refer to as a "contactor").

 

One of these relays will prevent a 3-way refrigerator from being operated on 12V unless the motorhome's engine is running. If no fridge-relay were fitted and the refrigerator could run on 12V without the battery from which it is receiving power being charged, that battery would rapidly be flattened.

 

The 2nd relay isolates many of a UK-built motorhome's 'domestic' services (eg. reading lights, water-pump, hob/oven 12V gas-igniters) when the motorhome's engine is started. Installing an isolation-relay seems to be something only UK motorhome manufacturers do and stems from concern in the mid-1990s that electrical interference from a motorhome's 12V domestic services might adversely affect the vehicle's critical systems (eg. ABS).

 

Assuming that your motorhome's system is based on a Sargent unit, the warning message referred to should be of no concern. This example of Sargent control-panel User Instructions

 

http://www.sargentltd.co.uk/PSU_2007_User_Instructions.pdf

 

includes on Page 9 of 11 details of a message "System disabled - Engine Started", describing the meaning of this message as

 

"This WARNING display indicates that the system has been disabled because the vehicle engine is running".

 

This just indicates that the isolation-relay has been triggered and I would expect the message to appear temporarily on the control-panel display every time the motorhome's engine is started. Presumably the rationale behind providing this Warning Message is that a motorhome owner unfamiliar with UK motorhome electrical-system norms might otherwise believe there was a fault when, having started his/her motorhome's engine, most of the living-are electrical services no longer function. However, if the Warning Message appears when the motorhome's engine has not been started, something odd is going on.

 

If there's a persistent rattling/clicking noise that clearly involves a motorhome's electrical system, a relay should be considered a prime suspect. In your case, as the rattling problem is sporadic and the noise comes from the fridge, it's possible that the fridge-relay is on the way out. This relay is usually at the rear of the fridge and (if accessible via a fridge ventilation-grille) easy enough to replace.

 

I suggest you let a 'professional' check this problem out, though it's fair to say that, unless the fault is evident when you take your motorhome for repairs next week, or the fault can be provoked at that time, fixing it on a permanent basis may prove difficult.

 

I also suggest that, if you can get the fault to occur between now and next Wednesday, you carefully note the characteristics and try to identify accurately where the noise seems to be coming from. While "...a rattling noise...somewhere in the Dometic fridge..." is OK, "...a rattling noise...from the rear/top/wherever of the Dometic fridge..." would be more helpful to a technician.

[sshortcircuit]

I can get the same problem on my Kontiki with the dometic fridge and this was down to a faulty fuse/fuseholder at the split relay in the engine compartment. Not sure what your MH is but worth a check first.

[Keithl]

Cliff,

 

In response to Derek and SS's posts have you checked your relays and fuses which will be located under the bonnet close to the engine battery?

 

If you follow the wiring from the battery positive terminal you should find 2 relays and fuses nearby, on our Merc they are fixed to the side of the heater casing within 12" of the battery. Also then follow the wiring as on our's there are connections half way across the scuttle below the windscreen.

Remove and refit each fuse and relay and part and check each connection you can find. Also look for any signs of overheating or burning as this is a sure sign of a poor connection.

 

Keith.

[Cliffy]

I have done some further investigation today and found that the step does not retract when the engine is started as it should but works off the manual switch when the engine is running which it shouldn't also when I operate the manual switch the engiine running warning goes off and evrtything works as normal.

I have checked and cleaned the fuses and relays under the bonnet as sugested which made no difference. I now think it could be the step relay but have yet to find where it is. I assume it is under the cover around the step motor and being directly behind the rear wheel is in a prime position for water ingress. The MH is in for a service and MOT tomorrow so I will not be able to do any more until that is done.

[Derek Uzzell]

Cliffy - 2012-09-26 8:19 PM

 

...I now think it could be the step relay but have yet to find where it is. I assume it is under the cover around the step motor and being directly behind the rear wheel is in a prime position for water ingress...

 

Most unlikely that the step-relay will beneath the step-motor cover.

 

Electric steps can be fitted so that their extension/retraction is solely via a manually-operated switch, or via a manually-operated switch plus automatic retraction when the motorhome's motor is started. In the latter case the automatic retraction option involves fitting a supplementary relay triggered from the motorhome's ignition circuit.

 

You haven't said which make/type of step you have, but it's probably an Omnistep (and, based on your "cover" mention) a swing-out type. The links provided in this earlier thread may be helpful

 

http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=28366&posts=8

 

As you say, fitting the relay under the step's motor-cover would make it vulnerable to water and road-muck. It would also make the relay much trickier to wire up than if the relay were inside the motorhome.

 

No idea where Auto-Trail might have put a step-relay in a 2004 Tracker, but another forum member may know. (Perhaps Auto-Trail puts it near to or behind the fridge?).

 

There's a logical link between the step-relay and the fridge-realy, in that both will involve the vehicle's ignition circuit, so your 'rattle from the fridge' and your step not retracting automatically may be related somehow.

[casey]

Hi Cliffy,

Had a similar problem with the electric step and fridge when we first bought

our Dakota, it turned out to be a blowm fuse next to the cab battery.

casey.

[Robinhood]

Derek Uzzell - 2012-09-27 9:40 AM

 

There's a logical link between the step-relay and the fridge-realy, in that both will involve the vehicle's ignition circuit, so your 'rattle from the fridge' and your step not retracting automatically may be related somehow.

 

Indeed there is a logical link, and potentially (especially if there is a failure somewhere) also a physical link, as the wiring diagram shows:

 

http://www.sargentltd.co.uk/Autotrail_schematics_2003.pdf

 

Note, the headline for the download says this is for 2003-2005 vehicles.

 

My suspicion would be a failed relay, or a short in one of the relly-protected circuits, but diagnosis at distance isn't very easy (nor in many cases, sensible ;-) )

[Cliffy]

I have removed and cleaned the fuses and the two relays near the battery which made no difference.

I would be happy to replace both relays but I can not see any referce numbers on them to order new ones. There are numbers on each of the 4 pins, from memory 30, 85,86 and 87. Where would I be able to buy new ones and how would I be sure I get what I need? Are the pin numbers all that is needed?

I have still not located the relay for the step. It may be inside the fridge cabinet as the cables go in that direction but it is not visible from the outside with the fridge vents removed.  

[crinklystarfish]

Those numbers are fairly standard throughout the industry for simple make/break relays and just indicate the low current and high current in / out terminals. Durite make pretty good 12V relays which are readily available from eBay or any decent automotive shop, for eg: http://www.thetoolboxshop.com/index.asp?function=search

I would think a 20Amp 12V make/break relay will be well up to the task of powering steps / fridge though it would be wise to check the current consumption of any devices the relay(s) service to be sure.

If you need further info or the numbers of the terminals explaining this is good: http://www.bcae1.com/relays.htm

[trigrem]

As Derek says it it unlikely that the step relay is underneath with the step, but if there is a switch at the rear of the step in order to switch off power to the relay when the step is retracted, If this switch is on the blink due to dirt then it would possibly cause the relay to chatter.

Doug

[Derek Uzzell]

crinklystarfish - 2012-09-28 8:26 PMThose numbers are fairly standard throughout the industry for simple make/break relays and just indicate the low current and high current in / out terminals. Durite make pretty good 12V relays which are readily available from eBay or any decent automotive shop, for eg: http://www.thetoolboxshop.com/index.asp?function=search

I would think a 20Amp 12V make/break relay will be well up to the task of powering steps / fridge though it would be wise to check the current consumption of any devices the relay(s) service to be sure.

If you need further info or the numbers of the terminals explaining this is good: http://www.bcae1.com/relays.htm

I think the relay for an Omnistep will be "changeover" type rather than simple make-&-break.Should that be where Cliffy's step-related problem lies, the 'correct' relay is readily available on-line:http://campingequipmentshop.co.uk/index.php/omnistor-omni-step-relais-for-step-12v-308200/p_616.html

[crinklystarfish]

More than likely, agreed,  but I was just responding to the reported finding of 4 pin relays with the terminal numbers specifed.

[Cliffy]

Thanks folks all seems to be working again.

There appeared to be two problems the step retracted switch was sticking. I removed the motor cover and cleaned the the switch with soft brush and suddenly the step retracted and the the buzzer sounded this being due to the PSU believing the engine was running which it wasn't.

So I could finish cleaning the switch I removed the relays next to the battery. When I refitted the relays the System Disabled Engine Running message was still displayed. As a last hope I swapped the relays over in their sockets and surprise surprise all was working fine again.

I will fit new relays though as there must be a problem with one of them.  I had cleaned them and the sockets a number of times and replaced them in to there original sockets and it had made no difference

Thanks for all the help I have had from everyone who replied to my posting.

 

[Keithl]

Hi Cliff,

 

VERY IMPORTANT - URGENT

 

By your diagnosis of swapping the relays as having fixed your 'system disabled' message I would now suspect that you have a shorted relay and you have now fitted it to your fridge circuit.

 

If you turn your fridge to 12v with the engine off does the fridge work, ie is the green(?) warning light on? If so be very careful as you could easily flatten your starter battery. I would strongly suggest removing this failed relay until you can source a replacement. Any good car accessory shop or caravan delaers ahould be able to supply one.

 

Keith.

[Cliffy]

Thanks for the heads up on that.

I did check for that and the fridge appears to work normally, the green light only came on when the engine was running. I have switched the fridge off though just in case.

I will get two new relays on Monday.

[Keithl]

Cliffy - 2012-09-29 10:32 PM

Thanks for the heads up on that.

I did check for that and the fridge appears to work normally, the green light only came on when the engine was running. I have switched the fridge off though just in case.

I will get two new relays on Monday.

But please can you confirm that if the fridge is left selected to 12v and the engine turned off that the green light goes out. If it does then I think a few further checks may be required as it appears both relays are now working.Keith.

[Cliffy]

Keith

Yes the fridge light does go off when the engine is turned off.

I am pretty sure that the faulty relay was the fridge/step relay which I have now replaced with the split charge relay so the fridge and step work correctly.

I have put the faulty relay in the split charge relay and it has been in for 24 hours with the van parked on the drive, in that time the leisure and engine batteries have now equalised there voltage, which they have never been before, this indicates to me that there is short within the relay. (It was passing (some) power to the fridge originally with the engine off and now in the other position it is passing power between the batteries).

I have removed the split charge relay now until I get a new one.(two actually)

If I am on the wrong track please let me know your thinking.

Thanks

Cliff

[Keithl]

Hi Cliff,

 

Now you have explained about the batteries equalising in voltage all is clear and I agree with you, you have one faulty relay where the contacts have welded together in the 'On' position.

 

Let us know what happens when you replace them.

 

Keith.

 

Edit to add that i think the faulty relay is the one you now have in the split charge and not on the fridge circuit. So agree, change both!

[Cliffy]

Fitted 2 new relays bought this morning from the local auto electrician (£6.99 Each) and all is back to perfect working order.

Took the covers off the old ones, one had rust around the pivot of the moving contact and was stuck partialy closed, scraped the rust off and tested it, it works fine now. Anyone one to buy two used relays going cheap, only 44000 miles and 8 years use. :-)

[Keithl]

Hi Cliff,

 

Glad you got it sorted!

 

Is it worth looking at somehow waterproofing the new relays or at least keeping any drips of water off them, maybe with a splash shield or rain cover above them?

 

But do not wrap them in a plastic bag or try and seal them as if you get condensation around them you will be back to square one.

 

Keith.

[Cliffy]

I did look at that but the are just hanging along with the associated fuse on cables close to the battery. It looks quite amateurish you would not think it had been done by a high end company such as Autotrail.

There is not enough cable to be able to fasten them back to the bulkhead and I don't trust myself to rewire them.

I supose if they last another eight years I can't complain .