RM7401L Fridge Selector Switch 2 questions plse?

[Mike800966]

Somewhere on here a brave chap dismantled one of these switches and cleared the fault, but I cant find the posting.
The second question is that the switch seems to control the electronic ignition, automatucally killing the sparker once a flame is established.
Does anyone know how it does it.? The immediate problem is that the sparker runs all the time and will burn itself out eventually.
I think it must get a signal from the gas valve and thats what the two thick black wires are for ie low resistance so as to send the thermocouple signal over from the gas valve to the switch, but then what does it do with the signal?
Over to you please
Mike

 

[68c]

I think the flame detector works using the principle that a flame conducts electricity, something to do with ionised particles. The electronics send a spark then detects if there is continuity through the flame, no conductivity it sparks again, all at electronic speed. Once lit it detects the flame and stops the next spark, if the flame blows out it automatically re sparks. It uses the spark wire as the sense wire, it is important that wire probe is in the flame once lit or it will not know there is a flame and so keeps on sparking.
Solution, make sure the wire spark probe is in the flame.

Edit. I may be wrong in that it senses conductivity through the flame, it may be the flame generates a tiny current within the probe, as in a thermocouple, either way a common cause of continual sparking after lighting is the probe not fully in the flame.

 

[68c]

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