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Old 07-03-2022, 09:40 AM   #1
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Dometic LP Cooling Issues

This video tells me why my fridge won't cool when it is not level:



But who can explain the following?

My rebuilt cooing unit was working great on AC. I switched to LP and it stopped working. I switched back to AC and it still would not work. I shut it off long enough for the boiler to cool. When I restarted it on AC, it cooled just as it had in the beginning. Can someone explain why it would not work on AC after I had tried it on LP?
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Old 07-03-2022, 11:43 AM   #2
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Thermodynamics
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Old 07-03-2022, 08:38 PM   #3
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Thermodynamics
That is a little vague.
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Old 07-04-2022, 07:05 AM   #4
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I agree with Old-Biscuit, and it is intentionally a little vague.

It is similar to an old style steam home heating boiler system only a little more complicated.

Oh wait, not many people left who have worked with a home heating steam boiler any more.

So, there are lots of possibilities. It could be some fluid got into a place intended to contain only vapor. It could be related to switching from electric to gas or more likely cooling the system down and allowing liquid to drain back into boiler.

It could be a safety circuit getting tripped. An "off" period and cool down cycle may have reset it.

It could have nothing to do with the above explanations. So answer is vague.
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Old 07-04-2022, 08:08 AM   #5
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...then allow me to clarify this scenario.

The system is functioning normally on AC.

Then you switch to LP which, due to a dirty orifice, reduces the amount of heat in the boiler to an insufficient level but does not eliminate the heat input entirely. The system stops cooling and the boiler temperature starts rising.

Then you restore the original sufficient heat source (AC) and the system simply continues to overheat.

Then you allow the system to cool by removing all heat to the boiler.

Then you apply the correct heat source (AC) and the system works correctly.

For reference, this unit has no thermal protection designed into the system...no safety devices other than the Fridge Defend.

We know that there are no blockages because the unit is new and because it works correctly with the correct amount of heat.

We know that there is fluid in the boiler because that is supplied by gravity. Unless there is some sort of blockage, gravity never fails.

We know that the AC is providing the right amount of heat because the system worked before and after the event.

What stopped the system from working when there was no blockage, it was level, and the correct heat was applied?

Thermodynamics may not be the answer. It could be chemistry.
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Old 07-04-2022, 10:24 AM   #6
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Thermodynamcs

the branch of physical science that deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and, by extension, of the relationships between all forms of energy.
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Old 07-05-2022, 08:02 AM   #7
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Thermodynamics is the study of the behavior of the heat. It does not tell you how materials will respond to that heat. For that one must look to physics and chemistry.

From Britannica:

thermodynamics, science of the relationship between heat, work, temperature, and energy. In broad terms, thermodynamics deals with the transfer of energy from one place to another and from one form to another.

From Britannica:

chemistry, the science that deals with the properties, composition, and structure of substances (defined as elements and compounds), the transformations they undergo, and the energy that is released or absorbed during these processes.

All that aside, naming the science at work will not help anyone better understand what is going on inside a system. Why would the identical amount of heat applied to the system create two distinctly different outcomes?
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Old 07-10-2022, 11:28 AM   #8
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RV Fridge Boiler Dysfunction or Discontinuous

Quote:
Originally Posted by ChuckerF14 View Post
This video tells me why my fridge won't cool when it is not level:



But who can explain the following?

My rebuilt cooing unit was working great on AC. I switched to LP and it stopped working. I switched back to AC and it still would not work. I shut it off long enough for the boiler to cool. When I restarted it on AC, it cooled just as it had in the beginning. Can someone explain why it would not work on AC after I had tried it on LP?
Sorry, I have been out consulting and am glad to get back to helping folks with their fridge issues. And, thanks for posting the YouTube video.

Frankly, with the expertise here on iRV2 I would think someone would be able to get a little deeper than saying that it is thermodynamics.

To answer your question, you stated that "switched to LP and it stopped working". This indicates that it was a heat issue, we did do a post on "Quality of Heat" where we explained that the proper amount of heat had to be delivered to the boiler of the absorption fridge.

What I assumed occurred, when you were in the LP Gas mode of operation, there was not enough heat, and the boiler quit pumping ammonia. This is why the fridge stopped working.

When you "switched back to AC and it still would not work", there was no ammonia in the boiler, therefore the boiler pump would not restart.

By "shut it off long enough for the boiler to cool", the ammonia returned to the boiler and the fridge started like normal.

In the YouTube, you see after the 6th time the fridge overheated, the fridge was leveled and it restarted. Your fridge most likely boiled the water in the system, and it took time for the ammonia to return to the boiler.

If I were to guess, I would think you shut down the fridge over night?
I say this because we have extensively tested both Dometic and Norcold RV refrigerators, and when the water in the system is allowed to boil, it takes up to 12 hours for the ammonia to return to the boiler.

Thanks for using iRV2
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Old 07-10-2022, 12:42 PM   #9
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A thoughtful response...finally. Thank you!

This all makes sense now. It sounds like boiler chemistry....caused by heating without percolation.

When I look at the video again, it is apparent that the system comes close to overheating on the first start in zone 3, even after the fridge is placed back in a level orientation. This must have been due to ammonia depletion during the previous overheat conditions.

It seems to be a similar response to the lack of percolation, ammonia depletion. In my case it was due to inadequate heat. In your demonstration it was due to blockage caused by the out-of-level orientation.

Would you agree?
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Old 07-10-2022, 04:20 PM   #10
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Out-of-level orientation versus lean ammonia condition

Quote:
Originally Posted by ChuckerF14 View Post
A thoughtful response...finally. Thank you!

This all makes sense now. It sounds like boiler chemistry....caused by heating without percolation.

1) When I look at the video again, it is apparent that the system comes close to overheating on the first start in zone 3, even after the fridge is placed back in a level orientation.

2a) This must have been due to ammonia depletion during the previous overheat conditions.

2b) It seems to be a similar response to the lack of percolation, ammonia depletion.

3) In my case it was due to inadequate heat.

4) In your demonstration it was due to blockage caused by the out-of-level orientation.

Would you agree?
I am impressed, are you an engineer? I ask because you seem to be able to read a data collection curve and make practical decisions.

1) "it is apparent that the system comes close to overheating on the first start in zone 3", yes this is due to what is called Latent Heat. Some folks that operate boilers may not know about Latent Heat if they are operating a supper heated steam boiler.

The absorption refrigeration boiler is more of a distillation process than a power generation process. Power generation uses only water, where as a distillation process has a solute and solvent. The solute is the substance that is being dissolved, which is ammonia in the absorption fridge case. The solvent is the dissolving medium, or water in this case. The water is not only the solvent, it is also the absorbent because ammonia has an affinity for water.

When you open a bottle of household ammonia, typically 12% ammonia, the ammonia is very volatile. The ammonia evaporates into the air, and then the water in your eyes absorb the ammonia, and your eyes burn

Thanks for posting the video, I did not think anyone would see it. I posted it to YouTube before I left on an RV consulting job. I have not quit my daytime job to become an iRV2 social media mega poster

2) "This must have been due to ammonia depletion during the previous overheat conditions.", you nailed it, if you can fly an F14, and do the engineering, our country is in good hands as far as defense, thanks for serving

3) "In my case it was due to inadequate heat.", that is correct. This is because low heat makes small bubbles that just run up the pump tube without displacing any water. It is by displacing the water with ammonia that the pump works.

In this last comment comes "disinformation", which I address next:

4) "In your demonstration it was due to blockage caused by the out-of-level orientation.", this has been promoted for years due to how the older absorption refrigerator boilers were made. It is fairly rare in newer refrigerators to get "blockage", the issue is that the sodium chromate inhibitor is depleted with heat. Ammonia eats through the steel tubing of the cooling unit without sodium chromate to protect the cooling unit. This is how fires are caused. The heat does not affect the ammonia nor the water in the cooling unit.

So, short answer: NO, in our demonstration where we are tilting the cooling unit at 3 degrees off-level, the boiler is overheating because the ammonia is pooing in the tubing, thus it does not return to the holding tank. By Latent Heat, the boiler runs at a low enough temperature that the water is not allowed to boil in the system. When the boiler has no ammonia, the boiler overheats if one does not have a Fridge Defend (period)

Keep the great questions coming

I am here to break the disinformation promoted for years about absorption refrigeration It is hard to turn the tide, folks develop bad habits when they are not aware how a system works.
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Old 07-10-2022, 09:59 PM   #11
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RV Fires

Just to add my own 2 cents, I am employed as a Legal Investigator for three major personal injury law firms and have first hand knowledge of the devastating results ANY rv fire can have. There are many causes of an RV fire including electrical failures, propane leaks, as well as the appliances, and more. Personally, my RV is equipped with a Fridge Defend and I am glad that it is installed and performing as it should. I have no worries about the fridge operation. I think the biggest reason to have a Fridge Defend is simply "peace of mind." The minimum cost for the device is well worth it, in my personal opinion, just to protect you, your family, and pets, etc.

I purchased and installed the unit myself about 18 months ago or so. It has only tripped during one trip to Quartzsite last Jan., several times, in the middle of the night. Other than that, I live at high altitude and everything works well with no problems. Paul and I concluded that the issue during that trip down to low altitudes in Arizona, was actually caused by a faulty LP regulator causing a low heat situation and thus a failure of the fridge to properly operate. Without the Fridge Defend, I would have had no idea that there was a problem at all, which could have led to a disastrous ending.

Just my own opinion, the Fridge Defend works and is well worth the minor cost. Paul has not paid or offered me any remuneration for my opinion. Get a Fridge Defend and sleep easier is my thought.,.
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Old 07-11-2022, 05:26 AM   #12
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Many Ways to Kill your Dometic or Norcold RV Fridge

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Originally Posted by Rmyron View Post
Without the Fridge Defend, I would have had no idea that there was a problem at all, which could have led to a disastrous ending.

Just my own opinion, the Fridge Defend works and is well worth the minor cost.
Thanks for your positive input.

I think that one of the issues that is missed here, and missed in its entirety by some of the posts is the fact that there are many ways that the boiler pump can stop functioning. And, that there is nothing on a Dometic or Norcold absorption fridge to detect when the boiler quits producing refrigerant. That is, nothing from the factory, the recalls and subsequent fire solutions do not detect the primary root cause of absorption fridge failure.

I welcome comment on the following, we apply science, just as a fire investigator does. But, one cannot challenge our findings by defining a branch of science, they need to use what they feel is fact or their opinion to challenge:

Many Ways to Kill Your Fridge

Thanks again for the right use of science, this is how safety is promoted
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Old 07-15-2022, 11:04 AM   #13
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When my wife and I bought our current motor home, there were a few different issues with the Dometic fridge. Come to find out the flue baffle was a wreck and the fans weren't operating, the burner was messed up and it wouldn't even operate on LP. In going through the whole system to get it up and running, I started doing some deep research on these systems and was pretty shocked on what I found and the potential hazards that are possible with these systems and not only the expense involved to fix them, but the potential hazards involved when things go wrong from no safegaurds in place. I have a solid mechanical background with the effects of heat and a pressurized unit that doesn't have a safegaurd in place to provide protection in case of too much pressure. There's a reason the hot water heaters in coaches and homes have a pressure relief valve but surprised these refrigerators don't. We've all seen stories on the news of hot water heaters in homes exploding from too much pressure built up. With safety being my first priority for my wife and I, we decided to spend the money and install Fridge Defend in our coach. When you consider the cost of it compared to the cost of the uncertain, it's a drop in the bucket and worth every penny and frankly, I'm surprised it's so affordable. The peace of mind we have now in knowing that we have a proven safeguard in place will only make our travels more enjoyable and I have peace in knowing that I'm protecting my wife in every possible way and being the good steward of her that God calls me to be. We have insurance for a reason. It's protection against the unknown and unexpected and Fridge Defend is insurance against a poorly designed system that did not put any safegaurds in place. Fridge Defend has my 100 percent support. A few hundered bucks for a one time investment to potentially save us from losing not only our lives but everything we own?? Worth every penny!
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Old 07-16-2022, 06:33 AM   #14
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Quote:
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When my wife and I bought our current motor home, there were a few different issues with the Dometic fridge. Come to find out the flue baffle was a wreck and the fans weren't operating, the burner was messed up and it wouldn't even operate on LP. In going through the whole system to get it up and running, I started doing some deep research on these systems and was pretty shocked on what I found and the potential hazards that are possible with these systems and not only the expense involved to fix them, but the potential hazards involved when things go wrong from no safegaurds in place. I have a solid mechanical background with the effects of heat and a pressurized unit that doesn't have a safegaurd in place to provide protection in case of too much pressure. There's a reason the hot water heaters in coaches and homes have a pressure relief valve but surprised these refrigerators don't. We've all seen stories on the news of hot water heaters in homes exploding from too much pressure built up. With safety being my first priority for my wife and I, we decided to spend the money and install Fridge Defend in our coach. When you consider the cost of it compared to the cost of the uncertain, it's a drop in the bucket and worth every penny and frankly, I'm surprised it's so affordable. The peace of mind we have now in knowing that we have a proven safeguard in place will only make our travels more enjoyable and I have peace in knowing that I'm protecting my wife in every possible way and being the good steward of her that God calls me to be. We have insurance for a reason. It's protection against the unknown and unexpected and Fridge Defend is insurance against a poorly designed system that did not put any safegaurds in place. Fridge Defend has my 100 percent support. A few hundered bucks for a one time investment to potentially save us from losing not only our lives but everything we own?? Worth every penny!
Thanks for the well thought out comments.

The hot water heater example is a good one. I wonder why a boiler operator would neglect this simple point when it comes to safety?

This statement says it all:

" A few hundered bucks for a one time investment to potentially save us from losing not only our lives but everything we own??"

I wonder why some of the folks on iRV2 point others away from safety
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