12v fridge fuse????

[Daveyfos07]

Hi folks,

We have come on our first long journey from Ireland to England. Everything was fine yesterday and then today while driving we noticed the fridge (thetford) was flashing so was not drawing any power from the vehicle battery.

When we got to our location I removed the van side panel and checked connections. All connections seemed tight so I started engine and put multimeter on input leads and it is reading 13.8v. I then removed the cover from back of the fridge and put multimeter on the connection inside there and its reading 13.8v.

So there is definitely power coming from the vehicle battery to the fridge but the fridge isn't picking it up.

The fridge is running fine on gas and EHU, it's literally only when driving that it is flashing with the error code 7.

The manual says error code 7 means no 12v supply to the fridge and to check the 12v fuse. However I have no idea where this fuse is and all my fuses are 10v, 20v, 50v etc.

The van is a Ford kentucky, 2008. There is fuses behind the glove compartment and fuses in the cupboard where the hot water container is. None of these fuses have a diagram so I have no idea what any of them are for.

Can anybody help or advise me on what may have happened?

To summarise:
- van was fine yesterday.
- left campsite this morning and noticed fridge flashing after about 2 hours
- checked connections behind panel and when engine is running power is going into the box on back of fridge however the fridge just flashes when we try to use that power.

If anybody could help me it would be much appreciated.

Many thanks

 

[paddymcc]

If there is a voltage at the 12v block at the back of the fridge then the fuse (if there is one, I don't think my fridge has one ) must be after that - so on the fridge itself perhaps? Can you find the output wires from the black box? They would go to the 12v element but might go via a fuse. If there is voltage at that point then I suspect that the element has failed.
Model of fridge and pictures of the black box might help.

 

[Daveyfos07]

Hey! Thanks for the reply!

The fridge is a thetford. Model B I think.

I've attached pictures from the back. The wires wrapped in insulation tape are just a standard white connector block and when tested have 13.8v coming in and 13.8v going out when engine is running.

The wires from this go into the black box to a white clip in connector. There is power coming to this as well when the engine is running. I can't see any wires or fuses between this box and the fridge, at least from the outside. Inside there is literally just a white connector that plugs in and I put my multimeter on the connector and there is power going from it to the black box.

This wee black box also has the input from EHU which works fine. It is literally only when driving the fridge goes off unless we switch it to gas which I don't like doing.

Thanks again

 

[autorouter]

Is it possible that the 12V element has failed? It looks as if the 12V from the alternator/starter battery is reaching the black box, and it's likely the 12V element is connected directly to that.

Can you disconnect one of the wires to the element, and get a resistance reading across the two element wires? The resistance reading should be about 1 ohm. That is difficult to measure accurately with a standard multimeter, it's about the lower limit.

Set the multimeter to ohms, on the lowest range, then touch the probes together and note the reading. That is the resistance of the test leads. Then probe the element wires, and note the increase. You should be able to tell if it's about 1 ohm, or if it's a short circuit which will be less than 1 ohm. Or of course it might have failed open-circuit, so it will show overload/overrange.

 

[Reallyretired]

The manual says error code 7 means no 12v supply to the fridge and to check the 12v fuse. However I have no idea where this fuse is and all my fuses are 10v, 20v, 50v etc.


Your fuses are all 12v, The numbers on them relate to the current in amps at which they will blow.

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[Pausim]

I have just been trying to make out the wiring diagram for a Dometic AES fridge. It appears to have 2 x 12V connections, one to power the electronics and a higher rated one to power the 12V element. It also has a D+ connection to activate the relay that connects the 12V heating element.

IF your fridge is of a similar type then you would need to check the fuses to all 3 connections. If the D+ is missing then the relay will not engage and if the 12V supply to the element is missing it can not power up. It would seem you have the 12V supply to the electronics because the other functions are working.

Your Thetford fridge may be entirely different but it would not surprise me if the 12V element had a separate supply.

 

[Daveyfos07]

Hi Guys,

Thanks again for the replies.

Here is a picture of the wiring diagram from the manual.

I usually just set fridge to Auto. Then it runs by vehicle battery when driving, gas when stopped and EHU when plugged in.

I can't see any relays or fuses near the fridge. But I have attached a picture of the wiring diagram and also my fuse box in the cupboard.

Many thanks once again

 

[autorouter]

As Pausim says, there are two separate 12V supplies. The Low Current (LC) supply powers the control board, which switches between 240V, gas and 12V, and controls the gas side of things. It is powered from the leisure battery, and should be on more or less permanently. It might have its own fuse, but more likely will be on a fuse with a few other permanently powered devices.

The High Current (HC) supply usually comes from the alternator/starter battery, and just powers the fridge 12V heater element. It will probably be switched by a relay on the 12V distribution board, so that it is only on when the engine is running. It will have a fuse of at least 20A.

Even though the HC supply is switched at the distribution board, the fridge control board still needs the D+ (engine running) signal for information during its automatic operation. For example it needs to know the engine is running so it can switch off the gas/240V automatically. Also there is a 15 to 20 minute safety delay when the engine stops before it switches on the gas, to avoid the gas firing up when you stop for fuel.

If the HC supply is reaching the fridge when the engine is running, it's possible the fridge 12V element has failed. It's not a big job to replace it, especially if there is access at the back through the vents.

 

[Daveyfos07]

Hi Guys, sorry for the late reply as I've been driving.

So I pulled the connection for the 12v supply out of the wee box, put it back in made sure it was tight. We left Salisbury with fridge on auto. It worked fine off the battery again. I thought happy days, it was just a loose connection. Then as we hit Birmingham the wife said the fridge was flashing again. Same problem.

We are at a campsite now and fridge is on EHU so I'm not worried too much, however I would like to know what this cause is. When I removed the box cover the connector beside the 12v connection had a thin cable tie threaded through it to make connection tighter so I nipped to Asda and bought some very thin cable ties and did the same just in case for some reason (probably age) the connection just isn't meeting properly or is slipping out easily when driving. Haven't tested it yet tho as now our webasto 3500 heater is throwing up an overheating code every 20 minutes !

Heating is running for 20 minutes then stops. 10 flashes. Diesel tank is full. Leisure battery is fully charged and i can't see any kinks in any of the ducts.

I despair lol ! First proper week away and these niggly wee problems are bugging the life out of me. All the camper dealers back home say I need to leave it with them for about 3 weeks which due to the racing schedule I can't do until the winter.

I'm reasonably competent at diagnosing stuff but this van just seems to have been wired by a guy who had a few too many beers on his lunchbreak on a Friday afternoon when it was being built.

That and I'm not 100% sure when the van has (if ever) been given a thorough habitation check and everything serviced and checked! It is 14 years old and although only bought for hauling motocross bikes around we would like everything to work as it should.

We now have a tiny oil filled radiator plugged into the mains to take the edge off the cold but with no heating it's going to be a cold night!

Help and advise is much appreciated

 

[Daveyfos07]

I also need to know which fuses do what. I'm assuming the fuses in the glove compartment are for the normal transit engine and the fuses in the cupboard are for the habitation area. Unfortunately none are labelled and I can't find any diagrams online. We have also found some wires in a cupboard above the rear bed above the garage which I have no idea what are for!

Campervan that Jack built lol

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[BouncyBoatFolk]

Just a thought, ours does similar on occasions. The cure was to turn it off completely at the fridge power switch, then turn it back on, at which point it would go to auto search for a power source, and as theengine was running pick the 12v supply. You can run with the gas on, but you need to fit a gas fuse, which will shut down the gas in the event of a RTA.
Mike.

 

[Daveyfos07]

I'm kind of hoping the connection was just a bit dodgy and the cable tie will hold it in place like the 240v connector beside it.

Really don't like driving with gas on, 2 MX bikes in the garage, a petrol inverter, a petrol power washer and 3 cans of petrol. It makes me nervous enough without adding gas to the mix lol

 

[Pausim]

Just a thought, ours does similar on occasions. The cure was to turn it off completely at the fridge power switch, then turn it back on, at which point it would go to auto search for a power source, and as theengine was running pick the 12v supply. You can run with the gas on, but you need to fit a gas fuse, which will shut down the gas in the event of a RTA.
Mike.

You need a crash safe regulator AND rupture protection on the gas cylinder. A crash safe regulator only shuts down the low pressure supply to the domestic appliances. Some gas cylinders like the latest Alugas ones have rupture protection built in, otherwise a high pressure hose with a rupture protection valve at the cylinder end is needed. LPG escaping from a ruptured hose escaping at 100psi doesn’t bear thinking about. Leaks from the low pressure side after the regulator will not be enough to trigger a rupture device or gas fuse. The vast difference in pressures on either side of the regulator mean that both need separate protection.

 

[irnbru]

Hi Daveyfos07 did you get to the bottom of your fridge problem? I'd love to know the answer. My thetford N3150 is also throwing up 12v error code 7. Checked the D plus signal and I think it was ok but now ive tried again I think its not.. All internet indications are to a faulty PCB. There are 2 fuses on the back of the PCB, one little glass and one 20 amp. My 20 amp one one blown and burn marks on pcb, I just had a new one delivered but its still throwing up no 7 error. Any help appreciated.

 

[GeoffnDee]

irnbru It could be worth double checking that there is 12v at D+ input connection at the rear of the fridge (engine running , fridge set to manual 12v) and that this connection is tight and clean.
Fault code 7 = lack of (or low) voltage at D+ or faulty PCB
There may be a fuse for the D+ supply on your PSU , depending on make and model of the PSU

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[irnbru]

Thanks, there is no D+ , Ive checked the fuses for the fridge 30A ad all is ok but where can i find the fuse for the D +? Im going to try the fuses at the front of van 2mor.

Does the D Plus come direct from the alternator or is it simulated? thx Sandra

 

[GeoffnDee]

What is the make and model of your habitation PSU ? (Sargent , Schaudt Electrobloc , CBE or other ?)

 

[irnbru]

What is the make and model of your habitation PSU ? (Sargent , Schaudt Electrobloc , CBE or other ?)

Hi Geoff its a CBE. I think Im confusing the issue with mis information I'm giving due to me keep swapping boards as I didn't want to drive yesterday with the new board in incase I damaged it, So I'm shortly going to swap the board again( getting really quick at this ) I will come back to you after I check all the voltage again, the figures and a photo of the Thetford fridge PCB which I know throws up fault 7. Be back soon. A local auto electrician wants £125 just to diagnose the fault.

 

[GeoffnDee]

The CBE system (DS-300 /200 PSU) has a fuse for the (simulated)out D+ it is fuse 10 and 3amps (far right),it also has relays for fridge etc in it. You may also find that your awning light is not switching off , if turned on , when the engine is started if the signal is missing.
There may also be a separate 3amp fuse from the ignition going to the Electronic battery separator , which is linked to the simulated D+.

 

[autorouter]

It's worth checking all the earthing straps and ground connections, including the main engine-to-chassis earth strap. Problems with these can mean the current from the alternator diverting along all kinds of weird pathways if the main route is blocked. For example I remember once hearing of a throttle cable getting red hot when the starter motor was operating, because it was the only earth path left.

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[irnbru]

Ok I made things worse I don't know if this happened last night while the old board was on or not, during the day (yesterday) I checked for a d plus signal and thought i had one, later I asked my partner just to verify my findings but there was no D plus signal. Being so scunnered by it all I left it til this morning. As per post no 18 above. So having swapped the boards around again for the new one. I went to turn on the fridge to take the readings but there are now NO lights on the fridge nor Truma control box. Whether this just happened this morning or not I dont know.

 

[irnbru]

UPdate coming up

 

[irnbru]

The CBE system (DS-300 /200 PSU) has a fuse for the (simulated)out D+ it is fuse 10 and 3amps (far right)

How one sentence fixed the issue. You saved my sanity never mind my purse. THANKYOU!

Having already replaced the blown fuse in my fridge pcb and it still not working. I replaced the whole pcb and still fault 7. I kept getting told about this D plus and to check my fuses. I had checked my fuses at the CBE unit several times, swapping boards back n forth and a lot of frustration and head scratching. but I didn't realise one fuse was missing (no9) so last night after checking the fuses again I must've returned fuse no 10 to no 9 (both 3 amp) and thats why there was no power to fridge or truma control panel this morning.

GeoffnDee sentence made me go look again and the missing fuse came to light. Not got another 3 I used a 5amp , not only did the truma control panel and the fridge LCD panel spring into life but the fault disappeared.


So happy, especially after taking it to a caravan auto electrician yesterday and he never picked up on this, instead saying my replacement board mightve been faulty as no D plus. Was supposed to return on Monday after the garage spoke to Thetford.

Getting really good at changing the PCB I then decided to try my old marked board once again. I had originally replaced the blown fuse on it at the very beginning of fault finding. Hey presto, this works now too. So I have a new spare board for future use.

How one fuse disappeared I don't know. I'm "guessing"it was during the hab check when the 12v fridge not working was picked up. Just a guess but no idea really. The van is almost out of warranty so it won't be going back to dealer again for any hab checks.

THANKS to all techies for all the help you give on this forum.