Question about absorption fridges

[GallenH]

Originally Posted by DaveWA

.
Camped without shore power for 5 days with fridge running on propane only. Freezer temp raised to 22F and fridge to 58F. Average outside temps were mid 40’sF and night and low 70’sF during the day.

I've dealt with a 3-way now for 6 years. Mine is smaller at 3.0cf so that might make a difference. From reading the forum, people usually get 30-50º difference between outside temps and fridge. You are only getting 12º from what you wrote above so it appears not normal to my eyes.

A guess: On my Dometic the burner sits under a tube which runs across the bottom of the fridge. After the burner the tube takes a right angle and proceeds up the side, entering a flue chamber where the AC and DC elements are housed. Is it possible that solids have built up inside the tube under the burner that would inhibit the heating at that point? If so that would affect the LP heating but perhaps not the AC/DC.

I'm just guessing here, others might have a better clue.

[JohnnyFry]

I suspect that something is wrong with your propane burner because propane is generally the highest performing of the three modes. If the burner flame oc correct it is possible that the control module is faulty.

[DaveWA]

Thanks! I dig a little deeper into this. Probably need to find a local shop that works on Dometic fridges.

[DaveWA]

Thanks for the feedback!

[DaveWA]

Originally Posted by DaveWA

Just wondering if you or anyone on this thread can confirm how my Dometic RML 8555 3-way fridge should perform when in Propane mode.

Fridge works perfectly on 110v mode, acceptably on 12v when driving, but very poorly on propane. What can I do to resolve the propane operation issue?
I have cleaned the burner orifice and exhaust, the burner fires up just fine and the flame looks good. I am just not certain what to expect in performance when the fridge is running on propane.

Example:

2/1/22 Went on 8 day trip to Death Valley.

With the fridge set (and left) on thermostat setting of 4 (out of 1-5 setting), prechilled the fridge on with the van on shore power 110v prior to leaving and it came down to -5F in freezer and 38F in fridge within about 6 hours. Outside temps were in the 50s. All is good.

Drove for 6 hours with the fridge running on 12v. Freezer was about 0F and fridge was about 40F when I arrived at my overnight destination. The outside temp during the drive was averaging in the low to mid 50’s F.

Plugged into shore power overnight and the freezer and fridge both dropped down a bit. Overnight outside temp was upper 40’sF.

Drove for another 3 hours with outside temps around mid 60’sF and freezer and fridge maintained temperatures.

Overnighted without shore power so fridge ran on propane. Freezer came up to 10F and fridge to 42F.

Drove 4 hours with the fridge running on 12v and freezer and fridge both dropped a few degrees, with outside temps around low 60’sF.

Trouble begins:
Camped without shore power for 5 days with fridge running on propane only. Freezer temp raised to 22F and fridge to 58F. Average outside temps were mid 40’sF and night and low 70’sF during the day.

Drove for 6 hours with fridge on 12v and freezer dropped to 18F and fridge to 50F.

Overnighted without shore power , fridge on propane, and then drove another 6 hours to get home with fridge on 12v. Freezer was at 10F and fridge at 45F when I arrive at home.

So. . . . . Is this what to expect from propane operation performance or is something wrong with the burner, exhaust, or other functions when in propane mode?

Your thoughts and experience are appreciated!

5/12/22: Additional info-
Took the van to the dealer today to have them check out the propane mode. They confirmed that the flame seems to be low, but the gas pressure to the burner is within specs. They do not know why the flame is low. They called Dometic and this fridge is no longer supported with replacement parts. The recommendation is to either live with unacceptable performance on propane (all is good on 11v and 12v) or replace with Norcold N4150AGR, which is an exact fit. Installed, the Norcold will be over $3k. Anyone have a similar problem when running on propane and a possible lower cost solution?

[Rlum]

Originally Posted by DaveWA

Just wondering if you or anyone on this thread can confirm how my Dometic RML 8555 3-way fridge should perform when in Propane mode.

Fridge works perfectly on 110v mode, acceptably on 12v when driving, but very poorly on propane. What can I do to resolve the propane operation issue?
I have cleaned the burner orifice and exhaust, the burner fires up just fine and the flame looks good. I am just not certain what to expect in performance when the fridge is running on propane.

Example:

2/1/22 Went on 8 day trip to Death Valley.

With the fridge set (and left) on thermostat setting of 4 (out of 1-5 setting), prechilled the fridge on with the van on shore power 110v prior to leaving and it came down to -5F in freezer and 38F in fridge within about 6 hours. Outside temps were in the 50s. All is good.

Drove for 6 hours with the fridge running on 12v. Freezer was about 0F and fridge was about 40F when I arrived at my overnight destination. The outside temp during the drive was averaging in the low to mid 50’s F.

Plugged into shore power overnight and the freezer and fridge both dropped down a bit. Overnight outside temp was upper 40’sF.

Drove for another 3 hours with outside temps around mid 60’sF and freezer and fridge maintained temperatures.

Overnighted without shore power so fridge ran on propane. Freezer came up to 10F and fridge to 42F.

Drove 4 hours with the fridge running on 12v and freezer and fridge both dropped a few degrees, with outside temps around low 60’sF.

Trouble begins:
Camped without shore power for 5 days with fridge running on propane only. Freezer temp raised to 22F and fridge to 58F. Average outside temps were mid 40’sF and night and low 70’sF during the day.

Drove for 6 hours with fridge on 12v and freezer dropped to 18F and fridge to 50F.

Overnighted without shore power , fridge on propane, and then drove another 6 hours to get home with fridge on 12v. Freezer was at 10F and fridge at 45F when I arrive at home.

So. . . . . Is this what to expect from propane operation performance or is something wrong with the burner, exhaust, or other functions when in propane mode?

Your thoughts and experience are appreciated!

It seems you fridge is still working although not great. It sounds like your propane pressure might be on low side. Do you have a tester? They are pretty inexpensive on Amazon. You want around 14 wc inch for optimum propane efficiency. When propane is a bit low, you will see inconsistent temp control. You might be running the propane pressure too low for the fridge to function on propane. Unfortunately, it is very sensitive at low propane pressure levels. If you get the propane pressure resolved and fridge is working. Get some internal fans to circulate the air in the box. I would not buy another 3 way for 3K. I would spend the money to upgrade the battery and get a compressor fridge. I believe you can get a compressor and lithium battery for less than 3K?

[DaveWA]

Originally Posted by Rlum

It seems you fridge is still working although not great. It sounds like your propane pressure might be on low side. Do you have a tester? They are pretty inexpensive on Amazon. You want around 14 wc inch for optimum propane efficiency. When propane is a bit low, you will see inconsistent temp control. You might be running the propane pressure too low for the fridge to function on propane. Unfortunately, it is very sensitive at low propane pressure levels. If you get the propane pressure resolved and fridge is working. Get some internal fans to circulate the air in the box. I would not buy another 3 way for 3K. I would spend the money to upgrade the battery and get a compressor fridge. I believe you can get a compressor and lithium battery for less than 3K?

Thanks for the quick response. The RV dealer tested the pressure and said it was to spec. I did not ask what the pressure was however and they did not note it on the W.O..I will check. Regarding the battery upgrade, I have flooded cell 6v golf cart batteries now with adequate power for current set up. To go to lithium batteries, I would need to change out other control panels, inverter etc, which I prefer not to (have already investigated that option). If I do change fridges, since a battery upgrade is not in the cards, I will stay with a three way absorption fridge.

[ChicagoTom]

Are you saying this happens all the time? If your fridge wasn't level during the boondocking time, then you won't get the performance. I'm guessing you know that. Don't listen to the service center, most are pretty clueless when it comes to accessories. Basically parts changers. First, you should just leave it on 5. I did this for over a year, and running 95% of the time on propane. Propane and 110 should be about the same. Again, wondering if this was a one time thing, or you're saying it's happened numerous times in different boondocking spots? Ex-HVAC Tech

[DaveWA]

Originally Posted by ChicagoTom

Are you saying this happens all the time? If your fridge wasn't level during the boondocking time, then you won't get the performance. I'm guessing you know that. Don't listen to the service center, most are pretty clueless when it comes to accessories. Basically parts changers. First, you should just leave it on 5. I did this for over a year, and running 95% of the time on propane. Propane and 110 should be about the same. Again, wondering if this was a one time thing, or you're saying it's happened numerous times in different boondocking spots? Ex-HVAC Tech

No, it does it all of the time on propane. I purchased the van used 2 years ago and this issue has been consistent. I have reached out to the RV service center to confirm what the gas pressure was (they had said it was "fine", but did not provide a pressure figure on the W.O.). Need to confirm that is OK. They said that the flame does seem very "small", so I wonder if I might have a problem with the gas valve (the GV100) per service manual. It looks like I might be able to get one from Europe as none show up in the States. I will also confirm that the flame does stay lit. It certainly does fire up just fine but maybe it is cycling on and off. I have wireless digital thermometers in the freezer and fridge sections and have checked progress from fridge off and the internal temps around 60f to fridge on in propane mode. At 24 hours freezer is 14F and fridge 47F. At 48 hours freezer 18 and fridge 49 and at 72 hours freezer at 14 and fridge at 46. If I use 110v mode, the freezer is sub zero at 4 hours and the fridge is 35.

Gotta be gas pressure, valve issue restricting gas flow, or flame cycling on/off.

[themexicandoctor]

This just arrived in my inbox but I can promise you, most of the Experts have spoken.

As an observer, my suggestion is talk to a different RV Repairman.

I do not recommend this but if the above is not convenient, at the very least, see if there is someone else more qualified in propane fridges, at the same company, to do an evaluation.

I ended up with a Novakool R3800 DC Fridge & apart from teething problems on my end (undiagnosed wiring issues), I am ecstatic 2 years later for many reasons; no need to level the rig, always works consistently with complete peace of mind.

Since you are not open to up "upgrading your Electrical systems" to move to DC Fridge like a Novakool, Isotherm or Vitrifrigo, MAYBE you have enough existing electrical horsepower to run a high efficiency, compressor chest fridge freezer as a replacement like an Engel, everything else pales by comparison.

Engels are Bulletproof, using a time honored, simple design that uses very little electricity. They can be connected to the cigarette lighter.

There are other companies out there but nothing performs as efficiently as an Engel.

Please note; I do know that when I went to replace my 3rd Dometic OEM Propane unit in 11 years, I could not figure out a way to configure efficiently any of (the best for me trade off wise in terms of physical capacity), compressor units on the market to fit in the original space of my fridge, in a Roadtrek Class B - I looked at every angle and the only way would have been purchasing a slide out tray, some carpentry work and the fridge sliding into kitchen area & it would have stopped 2 inches short against the bathroom door, on the other side of the kitchen & therefore I would have been unable to open the Chest lid all the way and or then conveniently access the entire unit. Otherwise I would have done it.

Maybe you, with your Lexor, takimg the Propane unit out & putting in the slide out tray with an Engel unit can work, the Roadtrek Bathroom door has a semi circular design that extends into this area.

Or you can reconfigure your existing coach in the seating area to make it work.

I had already taken my two passenger seats out upon purchase & added one full sized Wardrobe on the driver's side & a multi Storage Cabinet for medical equipment behind the passenger side (have lots of storage but no access through the side doors).

Below is a photo showing the previous fridge & my existing Carpentry which eliminated me building a storage cabinet to house a Chest Freezer.

As for Engels, on the Farm in New Zealand we have an Engel that is probably 50 years old the family use every year. One of the posters here, MSNOMER built in a cabinet/kitchen top with the Engel inside.

[ChicagoTom]

[QUOTE=DaveWA;139466]No, it does it all of the time on propane. I purchased the van used 2 years ago and this issue has been consistent. I have reached out to the RV service center to confirm what the gas pressure was (they had said it was "fine", but did not provide a pressure figure on the W.O.). Need to confirm that is OK. They said that the flame does seem very "small", so I wonder if I might have a problem with the gas valve (the GV100) per service manual. It looks like I might be able to get one from Europe as none show up in the States. I will also confirm that the flame does stay lit. It certainly does fire up just fine but maybe it is cycling on and off. I have wireless digital thermometers in the freezer and fridge sections and have checked progress from fridge off and the internal temps around 60f to fridge on in propane mode. At 24 hours freezer is 14F and fridge 47F. At 48 hours freezer 18 and fridge 49 and at 72 hours freezer at 14 and fridge at 46. If I use 110v mode, the freezer is sub zero at 4 hours and the fridge is 35.
Turn it all the way up, check to see if it comes on and stays on. While waiting, do a youtube to see what the flame should look like. In my case the flame looked fine, did all the cleaning orifice etc., but it turned out the igniter would be intermittent. On my ??54 the "Check light" would come on. I ignored it, and just reset, because then it would be fine for another 12-24 hours. (At the time I was living in it full time) LOL, I even had the replacement igniter. After about a year I finally replaced it, and never had the issue again.

[W9TR]

Absorption refrigeration works really well on propane. When you are level. If you want to move into the 21st century then get a compressor refrigerator and never look back. Just my opinion after owning both.

[GallenH]

ChicagoTom reminded me: have you cleaned the orifice? It's possible that a minor obstruction could diminish flow. It's usually after the pressure port that a tech would use to test the system pressure. On mine it just unscrews and the instructions are to soak it (in wood alcohol I believe) and blow it dry.

[folivier]

If there is room you could add a 12 volt muffin (computer cooling) fan to help circulate the air in the back of the fridge. That might help with cooling. If you power it by a small solar panel it will only work in the day when it's needed most.

[booster]

Before chasing other issues, the low flame thing probably should be resolved. The frig is probably just fine beyond that because it works well on DC and AC which usually work worse than propane.


Low flame is nearly always gas pressure or orifice plugging/size. Sometimes a gas valve not opening all the way, but rare that it would stick just enough to reduce flow a little.


I would start with the pressure and make sure it is at the high end of the specified range, not just "within spec". The range is big enough to make a considerable difference in capacity and flame size.


Then I would go back to the orifice and reclean and very carefully check the size and shape of the orifice hole. A cheapo set of gas welding tip cleaning reamers works very well and has less chance of damage compared to using a drill bit. If you can find a spec for hole size, that is a big plus because then a drill bit can be used from the non cutting end to check the size. Orifices are often, but not always, specified by a number like 59 which is a number drill size. Other times may be in decimal inches or millimeters and you would find the drill size on a drill bit size chart.


Also check upstream of the orifice all the way to gas valve and as far into the valve as you can reach.



You can get a manometer to read the pressure and a welding tip cleaner tool very inexpensively on Amazon and do it yourself. If you need to get it done by a shop try to find a propane hose maker and repair/install type company and forget the RV places.

[GallenH]

I doubt all rv techs are as competent as an actual Dometic tech. In terms of pressure the actual Dometic statement in it's service manual states

"The LP gas pressure to the refrigerator should be 11 inches water column with half of all BTU's of the RV turned on. With all other appliances turned off, the pressure to the refrigerator should not exceed 12 inches water column."

So that would mean that with other appliances off, the pressure should be between 11 and 12 IWC.

On some Dometic models there is a filter located at the inlet to the thermostat. If it becomes "saturated" It can restrict gas flow.

As mentioned earlier, orifice should be cleaned with alcohol solvent and blown out with compressed air (Dometic says at least once per year).

[DaveWA]

I called the RV dealer to confirm what the gas pressure is. He said the tech said 10.5” WC. Per the Dometics service manual, it should be 12” WC . I may try adjusting the pressure a bit to get it to 12". I was able to source a replacement burner as mine looks pretty tired. Not sure that will make the difference but cost was reasonable. I also shot a time lapsed video of the flame at 15 second intervals for 1 hour to see if possibly the flame was stopping and restarting. Started the fridge on gas and then started the video. See attached picture. Flame is blue with an occasional yellow burst. It did not shut off during the 1 hour time lapse video.

[GallenH]

First, I agree with booster: If it works on AC/DC it's not the absorption components (tubing, etc.) at fault. It's the LP burner. If it were me, I'd:

1. Remove orifice and clean it. That's easy. Unscrew, soak in alcohol and blow dry (use a compressed air can if you don't have an air compressor). Inspect the orifice. Make sure it's the correct number for your unit and someone hasn't replaced it with a different one (check your manual on this). Inspect for damage to ofifice. Someone might have tried to enlarge it, etc. If all looks ok, replace cleaned orifice.

2. Make sure that the burner is clean. I believe you said that you did this but the flame should be blue, ideally without any orange or yellow flare ups.

3. Set the pressure at the fridge (via the main regulator). From the posts and from Dometic's own recommendations you can see that 10.5" is too low. I'd probably go with 11.5 (with all other appliances off) to start and see if that improves the quality of the flame. Learning to use a manometer is not that hard. I had never used one before and I learned it was pretty easy. If you can do that, you don't have to rely on some RV tech and know for sure that you've got it set correctly.

You should be able to find some service information online from Dometic. I did but mine is......old, and probably does not apply directly to yours. I was able to find a guide specifically for techs servicing the Dometic fridges. So you should also. I know that it's sometimes easier to just let some RV place do the repairs. But I've found that many do not do a good job; much less than if you learn and do it yourself. Good luck