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Old 05-02-2022, 06:59 PM   #1
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Fridge Gas burner runs constantly

I have a Norcold N8X.
In AC (Auto) mode, it will draw the expected 3amps of shore power and the freezer and fridge will cool down to the desired setting. In AC (Auto) mode it will cycle on and off as expected (as indicated by the shore power increased/decrease of the 3amp draw).
(Auto mode is the automatic switching between AC to Gas when shore power is removed, then Gas to AC when shore power is restored)
The problem is: When switching to Gas (Auto) via removing shore power, the gas burner ignites and never shuts off.
- the unit has already been on AC for quite some time and has reached its set point- so why does the gas burner come on, and stay on?

- Iíve checked all connections, wiring, everything is clean.
- Door seals are good
- The thermistor is connected and tight to the fins AND must be working, otherwise one would think the AC would never shut off.

Iím thinking, since the single thermistor controls the circuit boards cycling of the AC relay and Gas valve relay/ignition- there must be a problem with the Gas cycle relay (or circuitry) of the control board. (i.e. thermistor signal failing to be detected by the Gas control of the CB- within the CB)
Is there a field replaceable part for said relay on the CB? or am I looking at a CB replacement?
Controls Board is Norcold 638189

Thanks!
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Old 05-02-2022, 07:23 PM   #2
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With gas flame ignited/staying lit does the fridge temps continue to decrease (get colder and colder)?

Do fridge temps get warmer?

Do fridge temps maintain same as AC temp?

Fridge temps get colder and colder....then new circuit board

Fridge temps get warmer......burner assembly needs cleaning (Polar Series have issues with Gas train)

Fridge temps remain same....maintain temp --- then LP is working
*could be dirty flue/flue baffle and not as much heat being transferred....just enough to maintain fridge temps
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Old 05-03-2022, 05:15 AM   #3
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Norcold N8X

Quote:
Originally Posted by 2Wayne View Post
Norcold N8X.
1) In AC (Auto) mode, it will draw the expected 3amps of shore power and the freezer and fridge will cool down to the desired setting.

2) The problem is: When switching to Gas (Auto) via removing shore power, the gas burner ignites and never shuts off.

3) the unit has already been on AC for quite some time and has reached its set point- so why does the gas burner come on, and stay on?

4) Iím thinking, since the single thermistor controls the circuit boards cycling of the AC relay and Gas valve relay/ignition

5) there must be a problem with the Gas cycle relay (or circuitry) of the control board. (i.e. thermistor signal failing to be detected by the Gas control of the CB- within the CB)

6) Is there a field replaceable part for said relay on the CB? or am I looking at a CB replacement?
1 & 2) What you have determined is that the cooling unit works fine, that there is a problem with the propane side of the fridge.

3 & 4) Check the simple things first, control boards are the last thing to test.
As mentioned below, the set-point is the same to turn on the shore power or propane source. But, due to control board design there is 'hysteresis' built into the temperature controller. Both my Norcold & Dometic will turn on when switching from shore power to gas, the 'hysteresis' of the controller is the best way to explain this.

5) The 2 relays that controls the propane and the relay that controls the 120VAC shore power heat source are controlled the same way inside the controller.

a) If your propane burner never turns off, then the relay may be stuck. See this from our website menus: Install Dometic Norcold > Norcold Install by Model (drop down menu) > Use the search and type in N8X:

Flash red on 5 time, off 5 seconds, repeat
LP Gas Flame when flame should not be lit.
Check the voltage to the LP gas solenoid, if there is voltage when there should not, the relay is stuck on the control board, see row above for suggestions.
The LP gas solenoid valve is stuck open, clean with solvent.
Click here for filter cleaning and LP pressure adjustment.

b) If the propane burner is not turning off and the fridge is getting warmer then there may be a problem with either the LP Gas pressure or the LP Gas filter. To solve these issues we have photos and instructions here:
Fridge Troubleshooting (menu) > Norcold Troubleshooting (drop down menu) > LP Fuel Filter (sub-menu)

Please report back, I have another customer with this same issue, if there is a stuck relay, it would be good to know that this is a problem with this particular board. Thank you
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Old 05-14-2022, 09:01 AM   #4
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Update to Fridge Gas Burner always runs constantly

thanks for the replies and suggestions guys!

So hereís an update
(I liked Fridge Defends bulleting his reply comments- so I per bulleted mine in the event anyone wants to reference a step)

1) The Norcold N8X was run on shore AC power with some water bottles in both compartments and I put an indoor/outdoor thermometer in the freezer section with the outdoor probe in the fridge.
The only way I can tell if the AC is cycling on or off is by the 3amp increase or decrease on the load panel in the MH. Periodically checking that- I do see the HM load swings +3A/-3A from time to time. If I open the fridge door- in a few moments I do see the load go up by 3A.
Nothing else is powered on except for the Ďdeadí draw the MH has when house batteries are on.

2) After 12 hrs the freezer temp was -9 and fridge was 34.
Outside the MH ambient air temp was 79 and inside was 82.

3) I hooked up a VOM to the gas solenoid in hopes to capture any high/low voltage to the solenoid to indicate that the gas was cycling on/off.
I unplugged the AC shore power and the gas burner kicked in.

4)Voltage on the gas solenoid was 12.4vdc (house batteries are at 12.6), and I set the VOM to capture High & Low readings. This way- currently both are reading 12.4 but when I come back later if I see a low reading of 0v Iíll know that the gas did cycle off at some point.

5) 6 hrs later I checked the temps in the fridge and the freezer went down by only 1deg (now -6), and fridge went up by only 1deg (now 35). Ive never seen anything more than +/- 2deg change.

6) The gas burner never shut off- I never heard or saw it go off, and the low reading on my VOM never went to 0vdc.

7) Interesting thing though- my VOM high and Low were both reading 10.79vdc on the solenoid, and 11.6vdc on the control board. (Batteries were still at 12.6) Readings were taken from the signal + and - connections as well as signal + to ground.

I retired from 45 years of working for a major Automation Controls manufacture (Allen Bradley/Rockwell Automation) as a systems/Controls Eng and service Eng- and to me-

8) that sounds like some load or resistance has increased or changed between the battery and the control board. And I know at those low DC voltages thereís a risk that not all electronics will operate efficiently / correctly. Current demand (Amps) shouldnít knock down the Voltage level, to me thereís a resistance or load increase between the batteries and Control board- or a component breakdown in the control board.

9) Could something on the control board (i.e. capacitor) be heating up (via current) and failing causing a bleed to ground? (causing higher load?) Where would this extra load / resistance be coming from? House batteries are holding at 12.6

10) I checked, cleaned and reseated all connections.

11) When I plug shore power back in and the unit goes on AC, the Control board voltage comes back to 12.6 and stay there all the while on AC power.

12) I unplugged the AC again, the Voltage on the Control Board and Solenoid was at 12.4 and I had to leave for a 3hr errand. When I returned, the gas was still burning and the voltages were again 10.79vdc on the solenoid, and 11.6vdc on the control board.

13) Still havenít ruled out the suggestion of a dirty flue/flue baffle as I can understand the heat transfer problem- but how do you remove that and get in there?

14) Other than that- Iím thinking Iíve got a flakey control board. My wife mentioned to me that occasionally the unit wont Auto switch over to gas when the shore power is unplugged. (thatís news to me! Iím outside unplugging it and when she seeís the switch over fail she manually turns it to gas. Thanks for that late tidbit! )

Thanks for all the help- this site is my go to place to find answers from real users, or to just get a heads up on fixes before the problem shows up!

Wayne
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Old 05-14-2022, 12:40 PM   #5
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As posted earlier.....

Fridge temps remain same....maintain temp --- then LP is working
*could be dirty flue/flue baffle and not as much heat being transferred....just enough to maintain fridge temps


IF fridge is in slideout you can access top of flue via the upper sidewall vent
If fridge is NOT in slideout..have to remove roof vent

12Ga shotgun brass brush .....do a 'chimney sweep' of flue
*flue baffle not listed but should have one hanging via wire clip at top of flue...unclip and remove to sweep flue
Wire brush the flue baffle

Lay cloth over burner to keep debris out...clean up after sweeping flue

OR.....using high air pressure blow up into flue while banging on it
*not best way but will should if chucks falling out if dirty


Otherwise.....LP pressure may be low..just enough to maintain cooling process but low enough to NOT generate sufficient heat so cooling can cycle


***the 10.8VDC at gas valve solenoid is OK
Gas valve Opens or closes
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Old 05-14-2022, 04:17 PM   #6
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I never had an RV fridge that the flame gos out once it set to propane. I think that's how they work. Some of the models I have had would automatically adjust the flame size to very small when colder demand was met. Other which were manual models you would set the flame size and that's what you had all the time,
Lots of things would get frozen.
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Old 05-14-2022, 06:49 PM   #7
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Quote:
Originally Posted by ArtJoyce View Post
I never had an RV fridge that the flame gos out once it set to propane. I think that's how they work. Some of the models I have had would automatically adjust the flame size to very small when colder demand was met. Other which were manual models you would set the flame size and that's what you had all the time,
Lots of things would get frozen.
If your fridge had Auto Temp Control or Adjustable Temp Control the propane turns on/off just like the electric heater.
Thermostat based on feed back from thermistor results in cooling cycles
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Old 05-15-2022, 07:47 AM   #8
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Check Gas Pressure and LP Filter

From one controls systems engineer to another, would you run a fired boiler without any protection at all?

Can you guess why the fired boiler will overheat without the proper heat input, that is too low of heat input?

If the fridge is cycling on shore power, but not in the LP Gas mode, then clearly there may be a, as we say in thermodynamics 'quality of heat issue'. One cannot look at the flame to know if you have the proper heat input.

Go to the signature just below, click on
'Click for Manuals & Troubleshooting Resources', go down to the
'NORCOLD RESOURCES',
click on 'Troubleshooting by Subject', then see the sub menu on this page,
click on 'LP Fuel Filter'.

See the 'Video #5', although this is a different model of Norcold, the principles are the same for checking the gas pressure and LP filter.

Installed many Allen Bradley Ladder Logic (PLC) controls . Do not ask me to deal with Latter Logic anymore, once I learned to code in 'C', never looked back!
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Old 05-22-2022, 04:13 PM   #9
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So- hereís the results:
I removed the roof vent to pull out the flue baffle and clean the flue- thereís no way I can reach the baffle. 1st Iíd have to cut through the mesh screen which is part of the roof flange, and even then it looks like the flue is about 3í down- and I canít reach that let alone get my fat arm down there. I can barely see the top of the flue, and I donít see the hook for the baffle.
Donít see a way of getting it out unless I remove the fridge

So, 2nd option: I removed the burner assembly, cleaned it up, and rapped on the flue. Some fine rust dust came out. Cleaned that up then took an air hose and blew up into the flue and around the area. I may just get some copper tubing and make an extension to my compressor nozzle, for my next trip up on the roof, and possibly snake it down to the top of the flue and blow down.
Attached is a pic I took with a round mirror of the baffle in the flue from the bottom looking up.
(Looks like a little bit of heat marks, sorry itís a bit out of focus)

Then, I cleaned the LP filter.

And guess what..? My gas valve now cycles!!!
(Just like I remember it did, and the UM sales it should)

So THANKS GUYS!!!
I guess it was a combo of rust dust and the filter.
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Old 05-23-2022, 06:21 PM   #10
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Good JOB! Great to hear you got it fixed and thanks for posting how you did it!
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Old 05-24-2022, 06:28 AM   #11
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Fridge Defend -- Troubleshooting Boiler Overheating on LP Gas Mode

Quote:
Originally Posted by 2Wayne View Post
So- hereís the results:
I removed the roof vent to pull out the flue baffle and clean the flue- thereís no way I can reach the baffle. 1st Iíd have to cut through the mesh screen which is part of the roof flange, and even then it looks like the flue is about 3í down- and I canít reach that let alone get my fat arm down there. I can barely see the top of the flue, and I donít see the hook for the baffle.
Donít see a way of getting it out unless I remove the fridge

So, 2nd option: I removed the burner assembly, cleaned it up, and rapped on the flue. Some fine rust dust came out. Cleaned that up then took an air hose and blew up into the flue and around the area. I may just get some copper tubing and make an extension to my compressor nozzle, for my next trip up on the roof, and possibly snake it down to the top of the flue and blow down.
Attached is a pic I took with a round mirror of the baffle in the flue from the bottom looking up.
(Looks like a little bit of heat marks, sorry itís a bit out of focus)

Then, I cleaned the LP filter.

And guess what..? My gas valve now cycles!!!
(Just like I remember it did, and the UM sales it should)

So THANKS GUYS!!!
I guess it was a combo of rust dust and the filter.
If you had a Fridge Defend you would have called me and said:

The Fridge Defend keeps tripping, and I would have asked you if the Fridge Defend trips on both Gas and Electric?

You would have tested it on Electric, and said no.

At this point I would have made the suggestions above, and this would have fixed the issue. Why? You will note that in the Dometic and Norcold manuals the amount of heat applied is critical to the operation of the fridge.

You where not getting enough heat due to a plugged LP filter most likely, because this fixed the problem. Too low of heat input results in small bubbles in the boiler. Just like in a pan of water on the stove, as the temperature rises, small bubbles form on the bottom of the pan, put no more heat in, and you have small bubbles and that is it.

Your boiler was overheating because the small bubbles running up the pump tube would not displace the water, thus the boiler pump action either is much slower or stops all together.

Being an engineer, you were paying attention, the question remains, as an engineer would you run a boiler without protection? When the boiler pump action stops, you are now destroying the fridge. Built in failure mode with no feedback systems (PLC ) to prevent boiler failures and ruptures.
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Old 05-24-2022, 03:01 PM   #12
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Safety -- It is everyone's business

I wanted to share an educational video that covers the concepts need to fix this fridge:

Click for YouTube Propane Safety Video

Hope this helps, knowledge keeps us safe
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