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Dometic fridge piezo starter question
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jetpoweredmonkey
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PostPosted: Sun Jun 05, 2011 11:25 pm    Post subject: Dometic fridge piezo starter question Reply with quote

Over the weekend I refurb'd a Dometic in a friend's 1991 Westy (after the standard "don't expect too much from it" disclaimer). It wouldn't run on propane. I updated it a bit with a new ball bearing fan, cleaned and resealed the burner box and jet and checked out the propane valves. Upon installation it fired right up on propane on the first try and got nice and cold overnight. I started it up half a dozen times after letting the burner cool off to make sure it was starting reliably, which it was.

Today when my friend came to retrieve the van, of course the fridge wouldn't start. The problem was obvious - no spark. Or rather, a few flashes of the spark indicator light every so often, then nothing. I sent my friend home and pulled the fridge back out after cursing for a few minutes.

On the workbench, the piezo igniter would not work even with 12V applied directly to its terminals. The culprit was the wire to the igniter probe in the burner box - it would sometimes spark if I wiggled it. Old wire, I guess. The sparks would fly with a test lead clipped into the output terminal. OK, no problem - I spliced in a new length of wire and we are good to go.

While I was troubleshooting the igniter, I couldn't figure out how in the heck the fridge signals to stop sparking. The igniter connects to +12V (through the gas selector switch), grounds in the middle of the fridge body, and has one more wire running to the indicator light. There is no ground interrupt.

I assume that the thermocouple cuts power to the igniter somehow once it heats up and starts generating voltage - but the only wire leading away from the thermocouple plugs in to the van wiring harness, not the fridge. Also, if you turn off the gas supply valve on the fridge control panel, the igniter starts sparking even before the thermocouple has cooled off.

How does it work?
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davevickery
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PostPosted: Mon Jun 06, 2011 6:56 am    Post subject: Reply with quote

From http://bryantrv.com/docs2/docs/Mandiag.pdf

The igniter reigniter, used on certain Dometic model refrigerators, operates on 12 volt current. On gas operation the igniter senses the resistance through the flame between the electrode and burner. When there is no flame at the burner, the resistance is high and the igniter begins sparking to light the burner. As soon as the flame is lit, the resistance between the electrode and burner drops and the igniter stops sparking. The resistance is monitored by the igniter, and, if for any reason the flame goes out, the igniter begins sparking until the burner is lit. This ensures that the flame will always be lit when desired. Each time the igniter reigniter system sparks, a light will illuminate on the lower left front corner of the refrigerator.

If the electrode does not spark first, make sure the igniter is receiving 12 volts. If the igniter is receiving 12 volts and produces no spark, it must be checked for operation:

(61) Turn the refrigerator off and remove the wire between the electrode and igniter. Now turn the refrigerator to the gas mode. If no internal clicking sound is heard the igniter is defective. It is important to remove the high voltage wire that goes to the electrode from the igniter when you are checking the igniter for operation. The high voltage wire and the electrode can be shorted to ground causing the igniter reigniter to think that the flame is lit, resulting in no spark on gas operation.

(62) The distance between the tip of the electrode and the burner, known as the spark gap, should be 3/16 of an inch. A greater distance will create a slow spark causing the light to blink. A lesser distance will create a fast spark that may not light the burner.
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jetpoweredmonkey
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PostPosted: Mon Jun 06, 2011 9:05 am    Post subject: Reply with quote

Jeez, Internet, take your time, I had to wait seven and a half hours for the exact answer I needed. Very Happy

Thanks a lot, that is great info and very helpful!
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