Norcold N841 Propane Problem

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Old 03-24-13, 12:16 AM
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Norcold N841 Propane Problem

In propane mode, the spark igniter lights the propane but the sparking continues for 20-30 sec and then the electric shut off valve closes and the flame shuts off. It seems like the igniter spark sense electrode doesn't recognize that that the flame is on. The error code is "NF", no flame. I changed out the electrode with a new one, cleaned all contacts, cleaned orifice but still the same problem. Next step is to change out the power board unless anyone has another solution. There are several postings on this exact issue, but no fixes that I've found.
 
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Old 03-24-13, 06:30 AM
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I just wanted to add that the OP is talking about a refrigerator.
 
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Old 03-27-13, 06:03 PM
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After cleaning, adjusting, and testing just about eveything I could think of that might be causing the electrode sensor not to sense the flame I ordered a Dinosaur board that should be here in a couple of days. To check the new electrode spark/sense that I thought would solve the problem I compared the electrical output of both this afternoon. Clamped the units one at a time in a vise at the collar around the porcelain and then checked output voltage by heating up the electrodes with a small propane torch. The old one reads 40-45mv and the new one 10-15mv max. Maybe after cleaning/massaging all the secondary stuff, if I had installed the old electrode the problem would have been solved. Guess I got too focused on assuming the spark/sense was bad. Will check that next. Did find out that flame position is critical to getting max output. Max output consistently occurs when the flame is directed at the end third of the electrode (getting hot flame on the tip seems to be critical). Wonder what min voltage from the sensor is needed to keep the 12v propane shutoff valve open? Haven't been able to find that anywhere yet.
 
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Old 03-27-13, 06:31 PM
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Welcome to the forums.

Doesn't the spark igniter/sensor rod have just one wire ?

I was going to wait for your reply but I decided to post this additional information for you.

That rod you were checking is just a piece of metal. It doesn't generate any voltage. It is a combination igniter and flame sensor in one. It carries the spark voltage to make the spark and it's also an integral part of the flame sensor circuit. When the gas valve opens and the burner ignites....the flame becomes a part of the circuit. This is called flame rectification. The flame is actually conductive and rectifies the flame sense voltage to ground. The board senses this circuit, knows the flame is lit, shuts of the spark and keeps the gas valve open.

There are three important points.

1) The rod needs to be kept clean. Take it out and use a scothbrite pad to clean it. The propane deposits a clear substance that hardens on the rod and it becomes an insulator.
(You changed your rod...no problem - keep it for a spare)

2) The electrode tip-to-burner air gap needs to be within 1/8" to 3/16"

3) The ground to the control board as well as to the burner is critical. The ground is part of the flame rectification path.

The link is the complete service manual for your fridge.

NORCOLD - N841 SERVICE MANUAL
And as always.....a special thanks to Chris Bryant of Bryant Services for hosting these manuals.
 

Last edited by PJmax; 03-27-13 at 09:16 PM. Reason: additional info
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Old 03-28-13, 12:14 AM
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Thanks for your comments, I'm trying to work my way through the process to fully understand how the system operates. To clarify the procedure I used to measure voltage generated by the sense electrodes, I connected one voltmeter probe to the insulated wire and the other to the metal flange (grd?) attached to the porcelain cylinder. When heat was applied to the electrode tip from the propane torch the voltage generated, I'm assuming, was the flame sense voltage required by the power board to know the flame is operational. In essence, isn't this the same circuit the board uses to determine if flame is present? Also, for both measurements the propane torch was the same distance from the electrode, I was surprised by the significant differences in voltage between the two.
 
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Old 03-29-13, 12:34 AM
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The voltages you were reading were mostly stray voltages and the flame was affecting your meter readings. The sensor rod is just a piece of high heat metal with a wire attached to it. The ceramic only holds the rod attached to the mounting bracket. You could connect the sensor/spark wire to a screwdriver and hold that in the flame. Same effect.

The control box applies an AC voltage to the sensor/spark rod. Once the AC signal passes thru the flame.....1/2 of the AC sine wave signal is rectified and converted to DC. That process allows a DC voltage to flow and that creates a current flow thru the loop.

So the signal leaves the control box......gets rectified in the flame and returns to the box thru the ground. The integrity of the loop needs to be maintained for the flame sensor to work properly. Kind of tough to explain. You can google "flame rectification" for more info.
 
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Old 03-30-13, 02:05 PM
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Thanks PJmax for your comments, I certainly have a much better understanding of the whole spark/sense function on these refrigerators now.

The bottom line at this point, after installing the new Dinosaur Power Board, is that the unit now works as it should when switched to propane. Upon start the electrode sparks 2-3 times after ignition and then stops and the flame continues until the box reaches the prescribed temp. Have gone through several full auto off/on cycles so assume the problem is corrected. I also installed an another ground wire from the circuit board to the frame to eliminate any future grounding problems. The Board, from Advanced Service and Parts, cost a little over $200 including shipping. Replacing the board took about 15 minutes, pretty straightforward, having a nut driver set was handy.
 
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Old 03-30-13, 02:09 PM
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I'm glad you're up and running again. Thanks for the update.
 
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