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Old 07-31-2022, 10:25 AM   #1
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Absorption fridge question

When running on gas, how does it regulate? I noticed on 120 volts that the power to the element shuts off when the fridge reaches the set temp, but what happens on gas? Does the gas valve turn off and on or is the flame always on?
I have some odd things going on and trying to figure it all out. This is on a 2011 Dometic RML 8555.
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Old 07-31-2022, 11:16 AM   #2
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Yes, the gas valve should regulate the flame. It shouldn't be always on.
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Old 07-31-2022, 11:32 AM   #3
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Yup, the 12 VDC powered PC board turns on/off either electric element or gas valve based on thermister temp reading and temperature setting (some models).
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Old 07-31-2022, 11:56 AM   #4
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What is happening is I am getting about 9 degrees colder on 120 volts than on gas. When the fridge was down to 29 I switched to gas and the temp rose to 38. The flame started immediately even though the fridge was down to 29. The boiler temp on 120V is around 314F but on gas it is even hotter, around 324F. I realize this discrepancy may be due to the fact that I am measuring boiler temp in the same spot while the 120V element and the gas tube are attached to the boiler tube in different ways/locations. So I am guessing my gas flow may not be as good as it could be. Disassembled the burner and cleaned everything last year, soaked burner and gently pushed a loose fitting tiny Acetylene torch cleaner thru it. Rig is stored indoors. Been testing in garage with a 80F ambient that has stayed pretty steady all week at 80F day & night. Have not opened door, using wireless thermometers. Also flue tube is clean and baffle in good condition.
Last year I remember fridge would get down to 31 at night on gas but outdoor temps were probably cooler.
Maybe mine is one of those that works best on 120V but I'd like to see if there's anything I can do to improve the gas performance.
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Old 07-31-2022, 12:06 PM   #5
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Certainly worth cleaning the burner tube again.


Doesn't take much for a rust flake/flakes to diminish burner output and therefore cooling BTU's.


And, if that does not increase the size of the flame, next I would check propane PSI (manometer). Low gas pressure will cause the same symptom.
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Old 07-31-2022, 12:15 PM   #6
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Not sure on the newer units with electronic ignition. But on the older ones that you had to light with the spark push button. It used a thermostat for propane that once the temp was met it reduced the flame size. So you always had a flame, large when there was a demand or small when no demand.

9 Degrees is a lot. I would be thinking that the the burner or orifice need cleaning??
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Old 07-31-2022, 12:35 PM   #7
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Your RN8555 is Euro Design and part of a series
RM8XX0, RMXX1 &RMXX5

'0' ---- Manual energy selection, manual ignition (gas flame lo/hi modulation)
'1' ---- Manual energy selection, Auto ignition (gas flame on/off based on thermostat/temp setting)
'5' ---- Auto Energy selection, Auto ignition (gas on/off based on thermostat/temp setting)

Should NEVER poke anything thru the gas orifice....it is a laser drilled metered hole. poking/high air pressure can damage it causing erratic flow

Have you check the Main LP System pressure?
Reg should maintain/control system pressure at 11"WC (0.4 psi) with at least 50% of appliances in service


Here is RM8 series manual
https://epi.dometic.com/externalasse...ref=-362595801
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Old 07-31-2022, 12:43 PM   #8
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The burner on my old Norcold rusted where the slots were and cause the flame to be deformed. It was enough to cause the frig temp to rise. Replacing the burner solved the problem.

Old Biscuit will have good advice when he comes along. One thing I believe he has mentioned in the past is that it's not a good idea to run anything solid through the orifice.

Edited: Ooops, OB posted while I was typing.
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Old 07-31-2022, 12:44 PM   #9
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Quote:
Originally Posted by Old-Biscuit View Post
Your RN8555 is Euro Design and part of a series
RM8XX0, RMXX1 &RMXX5

'0' ---- Manual energy selection, manual ignition (gas flame lo/hi modulation)
'1' ---- Manual energy selection, Auto ignition (gas flame on/off based on thermostat/temp setting)
'5' ---- Auto Energy selection, Auto ignition (gas on/off based on thermostat/temp setting)

Should NEVER poke anything thru the gas orifice....it is a laser drilled metered hole. poking/high air pressure can damage it causing erratic flow

Have you check the Main LP System pressure?
Reg should maintain/control system pressure at 11"WC (0.4 psi) with at least 50% of appliances in service


Here is RM8 series manual
https://epi.dometic.com/externalasse...ref=-362595801
I haven't checked WC yet, don't have a Manometer, thinking of ordering this one, it gets good reviews https://www.amazon.com/Hti-Xintai-Ma...NrPXRydWU&th=1
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Old 07-31-2022, 12:46 PM   #10
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Quote:
Originally Posted by bigb56 View Post
I haven't checked WC yet, don't have a Manometer...

You can make one for a few bucks-- plenty of "how too's".
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Old 07-31-2022, 12:51 PM   #11
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Originally Posted by wolfe10 View Post
You can make one for a few bucks-- plenty of "how too's".
I thought about that, I do have lots of clear tubing. Should I check the main LP pressure at any point? At the fridge supply? I'm assuming it should be the same at all points.
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Old 07-31-2022, 12:57 PM   #12
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Quote:
Originally Posted by wolfe10 View Post
You can make one for a few bucks-- plenty of "how too's".
Wood stand
Tubing
Ruler
Brass fittings
Colored water




Fridge gas valve has a test port.......easiest place to check system pressure

Stove top burners....stove has it's own Reg set for 10"WC so not good to measure system pressure





That one you link looks interesting/versatile/compact and easy to use
Good price also.
Post back how it works!
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Old 07-31-2022, 01:40 PM   #13
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So my next task will be pressure check and maybe cleaning burner again. Flame is blue and nice and steady. I remember last year when I took the burner out a small white filter that looked just like a slice of cigarette filter fell out of the burner inlet, it didn't get dirty and I put it back in with my fingers, hope that was OK.
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Old 07-31-2022, 03:10 PM   #14
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that is the ceramic filter on gas valve inlet

Clean it with spray electric contact cleaner or alcohol
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