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Dometic 7551 no ignition ticking noise on gas


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When you select 'gas' the yellow light on the front panel flashes quickly but there is no ticking sound.    There is 12v at the fuse box  and the fuse is good.   Removing the lower access panel I took the plug off the ignition unit and there is no 12v supply there.    Does anyone know which wire should have 12v on it?  

On the wiring diagram in the owners manual it shows three wires (see arrow at the very top) but no colours.   They all go down to the unit with the question mark at the bottom.   Could this be the switch on the front panel?  Any help much appreciated!

 

I forgot to say the fridge is working perfectly on mains and 12v, it's just the gas/ignition that is the problem.   (I did have the master switch on by the way!) 

 

 

IMG_20180530_165830511.jpg

Edited by Tintaglia
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I found that steveclc had a similar problem a year ago but not quite the same so I have messaged him.  

  He hasn't been around here lately so he may not get my message.   Thanks to his thread I checked the purple wire at the plug to the electronic ign unit and it had just less than half a volt on it instead of the 1. 5v on his.   I'm thinking perhaps the 12v supply from the fuse only goes as far as the PCB and then gets turned into 1. 5 to feed the ignition.     It seems that eventually his main fault was with the gas valve whereas mine is with the ignition.    I'd really like to hear more from Steve if anybody knows him and can get in touch.  

 

Thanks 🙂  

Edited by Tintaglia
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  • 5 weeks later...

Just updating this in case anyone else treads this way.   I confirmed that the 12v supply arrives at the PC board but it gets stepped down to 1. 5 v  upon leaving the board and feeding the (very expensive!) ignition unit.   I had noticed with a previous event of 'no ticking' a couple of years ago that removing the lower access panel outside and prodding the ignition unit plug got it going again.  

 

The fix this time was replacing the individual connectors in the plastic plug to the unit.   You can buy these connectors for a couple of pounds and you can crimp them to the wires yourself with a small pair of angled pliers and some patience.   The connectors can be fairly easily removed from the plug.   When you buy the new connectors it will become clear how they work.   I replaced the various crimped spade terminals I came across also.    If you want to do this you will need (inexpensive) standard criming pliers available at all car spares places.      

 

In my case the manufacturers of the fridge had cable tied the loom to the ignition unit tightly and with almost no slack, so I had to take the fridge out to allow me to pull through some more slack so that I had enough cable to fit the new connectors.    It was so nice to hear it ticking again!!

 

There are many other fridge faults like the fridge ticking but not lighting but my fault described here is restricted to a non-functioning ignition system.

 

Connectors- https://uk. rs-online. com/web/p/pcb-connector-contacts/7620698/

 

 

 

      

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  • 2 years later...
Posted (edited)

Just updating this once again!  This time the ignition was sparking but the spark was grounding to the wrong place!  See this video of the fault.  https://photos.app.goo.gl/LZoY5WKUd9KQKvSu7  My Dometic fridge (as per title above) doesn't have a thermocouple as such.   It uses a fully electronic equivalent to report the presence of spark and flame to the control unit and actuate the gas valve.  The new part comes with the burner for around £65.    

Edited by Tintaglia
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