Dometic RM7401 intermittent fault(s) in gas mode

[tallphil]

Hi, I have this 3-way fridge in a 2009 Chausson Flash 03.

 

Internittently, it will not light when set to gas mode. The igniter clicks and the spark is good but there's no gas arriving at burner. So I dismantled and thoroughly cleaned the gas injector assembly. The gas input pressure is fine. When it works, it works perfectly for many hours. So I suspected a sticking gas valve, a dodgy wire connection to gas valve, or maybe faulty control electronics.

 

After a few months the fault appeared to have become permanent, so just before removing the fridge from the van for repair, I tried it one last time, and I get a different fault - the igniter doesn't click. The yellow LED is on and stays solid, it doesn't change to flashing fault state after half a minute as it should. There is no gas and no spark. Nothing happens at all except the yellow light is on so I know the 12V PCB supply is ok. This suggests an electronic fault?

 

So I disconnect the fridge, pull it out of the van and hook it to a gas bottle and 12V supply. It immediately lights PERFECTLY in gas mode. Igniter, gas valve, flame detector, all perfect. I've switched it on and off 10 times. No problems at all.

 

All i can think to do now is clean and check all the electrical connections on the gas valve, igniter box and PCB, and put it back in the van. Whereupon we'll go on holiday somewhere hot and the faults will come back again....

 

Are there any other tests I can do, given that there is now apparently nothing wrong with the fridge? I don't want to spend £100s on new PCB, gas valve or whatever until I can prove there's something wrong with the ones I have.

 

Many thanks for any advice, Phil.

 

 

[Brian Kirby]

Do the other gas appliances all work normally irrespective of whether the fridge is working or sulking? Also, does the fridge exhibit this behaviour when other gas appliances are being used. The gas consumption of the fridge is very small so I'm just wondering whether the gas regulator is at fault and sometimes doesn't pass gas when the only consumer is the fridge.

[Robbo]

If you haven't done so already, I would replace the gas jet in the intake to the burner assembly. It's good practice to replace the gas jet whenever the fridge is serviced.

 

Also, there is a bracket attached to the burner assembly to support the igniter. Check there is no corrosion between the interface between bracket and burner assembly as this joint acts as an earth return. I found corrosion on mine, probably caused by the adjacent plastic condensation bowl overflowing. After cleaning up the joint the igniter system worked perfectly again.

 

 

[tallphil]

Thanks Brian, that's a good point, hadn't thought of that.

 

When the fridge won't work when we're away in the van, I often light the hob to check I have gas pressure. I can have one or all three hob burners going merrily and still the fridge won't light. So it doesn't seem to be the regulator problem you're thinking of. It would be nice if it was, because that's a cheap part to change!

 

But I seem to have just had a breakthrough. I've just tried the fridge again, and hallelujah, it didn't light. Seizing this opportunity, I wiggled all the spade connectors on the gas valve, and the ignition box connector - and it worked again. So I'm now pretty sure my problem is a failing wire or connector in that area. Tomorrow I'll take the wires off and check them all properly.

 

Cheers, Phil.

 

[747]

I would suspect a faulty printed circuit board.

 

These fridges really are poor but the replacement cost is horrendous, whether you need a new fridge or just a PCB. The PCB is well over £200 I believe.

 

Did you try the fridge by manually selecting Gas? My 7 series fridge/freezer currently has a faulty PCB, I just manually select Gas as the Auto function has failed (although about once every ten attempts, it will Auto select Gas when I switch off the engine).

[tallphil]

Thanks Robbo. I haven't replaced the gas jet, but I have had it out and boiled it until very clean! You're probably right I should change it soon.

 

And yes I will check that bracket for rust. On my previous motorhome I had a similar fault, except it was a rusty screw holding the ignition control box to the back of the fridge that turned out to be a dodgy earth path. I only found this out after replacing the box - expensive mistake!

 

Anyway I seem to have made progress on my fault - see my reply to Brian.

 

Cheers, Phil.

 

[tallphil]

Thanks 747. My fridge doesn't have the Auto function. I understand it's possible to upgrade it(?) but since I still have to manually turn on my gas bottle when I park the van, there doesn't seem much labour saved by having the fridge automatically switch from 12V to gas.

 

You're right the price of spares is very high, and the fridges are poorly designed. Anyway I seem to have made progress tracking down my fault - see my reply to Brian.

 

Cheers, Phil.

 

 

[Derek Uzzell]

My 2005 Hobby motorhome had a Dometic 7-Series non-AES fridge/freezer and this occasionally failed to relight automatically when running on gas.

 

There was no obvious pattern and I unsucessfully tried everything to stop this happening. I eventually noticed that one of the wires that push into the gas igniter box (photo attached) seemed a bit loose. After I had made sure that the wire fitted more tightly I don’t recall that the problem recurred.

 

(This might have been coincidental, of course, but it might be worth checking.)

[tallphil]

Thanks Derek, as it happens I have now traced the fault to exactly that place - my fridge has a P-810 igniter too.

 

My problem is that the spring-contacts in the connector have lost their springyness and are not making reliable contact with the pins on the P-810. I've extracted the contacts from the connector housing and attempted to bend the springy part of the contact with a tiny tool, whereupon it detaches entirely. The metal has clearly failed and I need new contacts in my connector.

 

After a lot of searching online, I think they are called JST VH-connectors and RS supplies sells a bag of 50 contacts for about £2.50

https://uk.rs-online.com/web/p/pcb-connector-contacts/7620698/?origin=PSF_435696|acc

 

I hope these are the right ones, I'll find out when they arrive next week.

 

[tallphil]

I might as well post the HAPPY ENDING to this story in case people with this problem are searching in future.

 

The connector on the P-810 ignition box is called a JST VH connector, and RS components sell both the plastic connector housing and the metal contacts that go in it. I just bought the contacts (bag of 50 for £2.10).

 

Once I'd removed the connector and all its wires from the fridge (this involves opening the PCB case on the top of the fridge and disconnecting the cable that links the PCB to the ignition box), and got a bag of new contacts from RS, it's quite simple to replace all the metal contacts in the connector using a soldering iron. The contacts are described as crimp-on, but I don't have the right crimp tool and soldering works just as well.

 

Four of the seven contacts in my connector had completely failed. This is fairly pathetic for an 8 year old product (cars contain hundreds of connectors of better design, and they generally don't fail if left alone). I replaced all seven and now have a robustly working fridge again!

 

There was some spare length in the igniter-to-PCB cable at the PCB end, which I've relocated to the igniter end, secured with cable ties. This might allow me to access all the ignition box wiring through the lower vent hole in future, without having to remove the fridge from the van.

 

Very satisfying to fix the fridge for £2.10 when Dometic charge so much for parts.

[Zanlin]

Reviving an older thread with a massive thank you to @tallphil

 

After calls around to get someone to look at the fridge I came across this post - my connector was in pretty poor state but I got some 'clicks' when prodding them with a multimeter.

 

Following the instructions - even with the part numbers :-D - I replaced the connector and it sprang into life on the third go. Been absolutely fine since then. I already had an igniter and burner on back order - now cancelled and a couple of hundred quid saved

 

Proof of the power of the forums and the kindness of people to share such useful information