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 > absorption refrigerator out of level, boiler temp control

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SJ-Chris

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Posted: 11/13/22 01:13am Link  |  Quote  |  Print  |  Notify Moderator

opnspaces wrote:

The problem with out of level is the refrigerant can pool and then cool in the upper tubes. Once cooled it can harden and block off the passage. Once hard there is no way to dissolve the deposits and you have to replace the cooling unit. This is typically not a one and done damage issue. It is usually cumulative and happens over time with repeated operation of the refrigerator off level.


This is one of the main things I'm trying to understand about the cooling unit operation while out of level. Assume for example the RV is parked on a steep driveway with the refrigerator on. What happens if the refrigerator is out of level and starting to overheat and the refrigerant cannot flow where it needs to flow. Then a thermostat cuts off the refrigerator power when the boiler temp hits 205*C and then turns it back on when it cools to 170*C and it just oscillates between 170*C and 205*C. Does any damage occur if left in this oscillating state for a few hours or even days? Would the refrigerant cool and harden and cause some incremental damage?

-Chris


San Jose, CA
Own two 2015 Thor Majestic 28a Class C RVs

Bobbo

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Posted: 11/13/22 06:22am Link  |  Quote  |  Print  |  Notify Moderator

SJ-Chris wrote:

This is one of the main things I'm trying to understand about the cooling unit operation while out of level. Assume for example the RV is parked on a steep driveway with the refrigerator on. What happens if the refrigerator is out of level and starting to overheat and the refrigerant cannot flow where it needs to flow. Then a thermostat cuts off the refrigerator power when the boiler temp hits 205*C and then turns it back on when it cools to 170*C and it just oscillates between 170*C and 205*C. Does any damage occur if left in this oscillating state for a few hours or even days? Would the refrigerant cool and harden and cause some incremental damage?

-Chris

Yes. The problem is when the refrigerator is running, it vaporizes the ammonia solution. That vapor then goes into the piping where being off level causes some of it to retain and solidify. It being subject to occasional shut offs doesn't prevent that. I am unsure if occasional shut downs would slow down the process because it is running less, or speed up the process because it has more cooling off periods for the ammonia to precipitate. It would definitely reduce the cooling efficiency inside the refrigerator.

I believe the only way to assuage your fear is to replace it with a compressor refrigerator.


Bobbo and Lin
2017 F-150 XLT 4x4 SuperCab w/Max Tow Package 3.5l EcoBoost V6
2017 Airstream Flying Cloud 23FB

SJ-Chris

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Posted: 11/13/22 04:09pm Link  |  Quote  |  Print  |  Notify Moderator

Bobbo wrote:

SJ-Chris wrote:

This is one of the main things I'm trying to understand about the cooling unit operation while out of level. Assume for example the RV is parked on a steep driveway with the refrigerator on. What happens if the refrigerator is out of level and starting to overheat and the refrigerant cannot flow where it needs to flow. Then a thermostat cuts off the refrigerator power when the boiler temp hits 205*C and then turns it back on when it cools to 170*C and it just oscillates between 170*C and 205*C. Does any damage occur if left in this oscillating state for a few hours or even days? Would the refrigerant cool and harden and cause some incremental damage?

-Chris

Yes. The problem is when the refrigerator is running, it vaporizes the ammonia solution. That vapor then goes into the piping where being off level causes some of it to retain and solidify. It being subject to occasional shut offs doesn't prevent that. I am unsure if occasional shut downs would slow down the process because it is running less, or speed up the process because it has more cooling off periods for the ammonia to precipitate. It would definitely reduce the cooling efficiency inside the refrigerator.

I believe the only way to assuage your fear is to replace it with a compressor refrigerator.


I have been trying to learn/understand refrigerator operation more so that I can best protect from overheating. Correct me if I am wrong, but the only thing that should be in the coils (top of the fridge down towards the bottom) is ammonium and hydrogen. These do not "harden" as they cool. The ammonium is a liquid. In the boiler it turns into a vapor and rises and then starts its journey through the coils at the top of the fridge on down towards the bottom (speaking in simplified terms here...). During this process, it is cooled and turns back into a liquid (it doesn't harden). So I'm not sure this is an issue.

One significant thing (most important?) to avoid during operation is having the boiler get too hot and boiling the water that is inside. This can be avoided with a thermostat (or Fridge Defend). If the water did boil and the boiler got too hot, then the rust preventative solution inside the cooling unit can start to crystalize (...builds up over time). This can weaken the rust prevention protection and cause the metal tubing on the cooling unit to start to rust. This rust can cause a rupture/leak eventually. This crystalizing can also ultimately cause blockages in some of the tubing. Having a thermostat (or Fridge Defend) will prevent this from happening.

One additional concern is too much pressure in the cooling unit. During normal operation it is under pretty high pressure (350-400psi). If the boiler/system gets too hot the pressure increases. If there are weak spots (due to rust) in the system it will put more stress on those spots and increase the chance of a rupture or leak. A thermostat (or Fridge Defend) will prevent this excess pressure.

So far, from my still limited understanding, I feel like if a thermostat (or Fridge Defend) is installed and it prevents the boiler from getting over 220*C (...I will likely set it to 205*C) then all of the above issues can be avoided.

Thoughts?

Thanks!
Chris

dougrainer

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Posted: 11/14/22 07:31am Link  |  Quote  |  Print  |  Notify Moderator

SJ-Chris wrote:

Bobbo wrote:

SJ-Chris wrote:

This is one of the main things I'm trying to understand about the cooling unit operation while out of level. Assume for example the RV is parked on a steep driveway with the refrigerator on. What happens if the refrigerator is out of level and starting to overheat and the refrigerant cannot flow where it needs to flow. Then a thermostat cuts off the refrigerator power when the boiler temp hits 205*C and then turns it back on when it cools to 170*C and it just oscillates between 170*C and 205*C. Does any damage occur if left in this oscillating state for a few hours or even days? Would the refrigerant cool and harden and cause some incremental damage?

-Chris

Yes. The problem is when the refrigerator is running, it vaporizes the ammonia solution. That vapor then goes into the piping where being off level causes some of it to retain and solidify. It being subject to occasional shut offs doesn't prevent that. I am unsure if occasional shut downs would slow down the process because it is running less, or speed up the process because it has more cooling off periods for the ammonia to precipitate. It would definitely reduce the cooling efficiency inside the refrigerator.

I believe the only way to assuage your fear is to replace it with a compressor refrigerator.


I have been trying to learn/understand refrigerator operation more so that I can best protect from overheating. Correct me if I am wrong, but the only thing that should be in the coils (top of the fridge down towards the bottom) is ammonium and hydrogen. These do not "harden" as they cool. The ammonium is a liquid. In the boiler it turns into a vapor and rises and then starts its journey through the coils at the top of the fridge on down towards the bottom (speaking in simplified terms here...). During this process, it is cooled and turns back into a liquid (it doesn't harden). So I'm not sure this is an issue.

One significant thing (most important?) to avoid during operation is having the boiler get too hot and boiling the water that is inside. This can be avoided with a thermostat (or Fridge Defend). If the water did boil and the boiler got too hot, then the rust preventative solution inside the cooling unit can start to crystalize (...builds up over time). This can weaken the rust prevention protection and cause the metal tubing on the cooling unit to start to rust. This rust can cause a rupture/leak eventually. This crystalizing can also ultimately cause blockages in some of the tubing. Having a thermostat (or Fridge Defend) will prevent this from happening.

One additional concern is too much pressure in the cooling unit. During normal operation it is under pretty high pressure (350-400psi). If the boiler/system gets too hot the pressure increases. If there are weak spots (due to rust) in the system it will put more stress on those spots and increase the chance of a rupture or leak. A thermostat (or Fridge Defend) will prevent this excess pressure.

So far, from my still limited understanding, I feel like if a thermostat (or Fridge Defend) is installed and it prevents the boiler from getting over 220*C (...I will likely set it to 205*C) then all of the above issues can be avoided.

Thoughts?

Thanks!
Chris


Your thinking is correct except about the blocking process. When the liquid cannot go from gas to liquid due to incorrect gravity, the liquid "adheres" to the area of the cooling unit just below the freezer coils. The actual process has never been completely explained to me how this gets "HARD". It just happens. It starts out gradually and everytime you run off level it adds a little more to that blockage. One day, your refer does not cool as expected. It still cools but not as well as new and is harder to cool in hotter ambient temps. The blockage has been described to me by both Dometic and Norcold at Tech schools as harder than a weld. The ONLY way to rebuild a blocked cooling unit is to cut out the top of the coil and weld a replacement. Blockage, the freezer will still appear to freeze, but will not get below 10 degrees which is spec. This is how when people sell their RV with a bad refer, they always show the freezer as "cold". But cold is deceptive, 5 degrees to 32 degrees will seem the same. One of my trainers from 40 years ago explained blocking as like Heart disease. You are born with a clear functioning blood artery system. But gradually over your lifetime, by eating the wrong foods, your arteries become slowly clogged. Then one day, you have a Heart problem and you think it "just happened". Your arteries are partially clogged, not instantly, but over years. Doug

SJ-Chris

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Posted: 11/14/22 10:00am Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:



Your thinking is correct except about the blocking process. When the liquid cannot go from gas to liquid due to incorrect gravity, the liquid "adheres" to the area of the cooling unit just below the freezer coils. The actual process has never been completely explained to me how this gets "HARD". It just happens. It starts out gradually and everytime you run off level it adds a little more to that blockage. One day, your refer does not cool as expected. It still cools but not as well as new and is harder to cool in hotter ambient temps. The blockage has been described to me by both Dometic and Norcold at Tech schools as harder than a weld. The ONLY way to rebuild a blocked cooling unit is to cut out the top of the coil and weld a replacement. Blockage, the freezer will still appear to freeze, but will not get below 10 degrees which is spec. This is how when people sell their RV with a bad refer, they always show the freezer as "cold". But cold is deceptive, 5 degrees to 32 degrees will seem the same. One of my trainers from 40 years ago explained blocking as like Heart disease. You are born with a clear functioning blood artery system. But gradually over your lifetime, by eating the wrong foods, your arteries become slowly clogged. Then one day, you have a Heart problem and you think it "just happened". Your arteries are partially clogged, not instantly, but over years. Doug


Good info. If that is the case, then it seems like anytime the refrigerator is far enough out of level and gravity flow cannot happen it has the risk of adding an incremental amount of blockage into the coils. Seems unavoidable. Does anyone know if blockage in these coils is a common (or rare) cause of cooling unit failures? What are the most common causes of failure? Holes/leakage? Blockage? (and if so, in which tubes?)

The question then becomes, "In a situation where the gravity flow through the coils is reduced or cannot happen because it is too far out of level, what effect does temperature (controlled by the boiler) have with respect to adding more incremental blockage?"

Would it be best to hold the boiler temp close to it's normal operation temperature of 180-190*C? Would it actually be BETTER to allow it to rise to 200-215*C to add pressure to the system and/or keep the ammonium mixture in a form that doesn't increase incremental blockage from happening? (I'm not sure if it works that way...) If the boiler temp got up to 205-210*C (indicating the fridge is off-level or there is some sort of blockage) would there be any advantage to the thermostat simply turning off the refrigerator until the boiler cools all the way down to 50*C (meaning the refrigerator (and boiler) would be off for probably 10-20 minutes)?


Sounds like having a thermostat on the boiler (Fridge Defend, or simple high temp thermostat) is a good thing to prevent the boiler from getting over 220*C and actually boiling the water and thus crystalizing the rust prevention solution, and also putting too much pressure in the system (thus reducing the chance of leaks or rupture). It would also prevent the boiler from getting up to 300*C, 400*C or however high it could get, thereby reducing the chance of a fire. But a thermostat would not do much/any good to prevent incremental blockage from happening if the gravity flow of vapor/liquid ammonium cannot flow properly through the coils.

-Chris

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Posted: 11/15/22 10:44am Link  |  Quote  |  Print  |  Notify Moderator

My experience with the Fridge Defend has not been a positive one and I always level the rig. It may work fine on a Norcold or Dometic system but does work for me on a Dutch Aire cooling unit with a Norcold control board.

What we experienced with the Fridge defend is that when it is cutting on and off (I think it is about a 20 minute cycle) it did not maintain adequate cooling. As set by the manufacturer, it cycled on and off even when level and not moving.

I put in a Dutch Aire cooling unit and a Fridge Defend last year. The fridge works great as long as I don't turn on the Fridge Defend. When I do, it turns the system off and on causing the system to go above 45 degrees. I texted back and forth with the manufacturer/creator of the Fridge Defend and was told that the Dutch Aire does run at a higher temp than others. He didn't give me any info on what to put the settings on for the Dutch Aire unit. His final statement was that the cooling unit is bad.

While in my drive way and perfectly level, I was able to change some of the setting on the Fridge Defend and get it to run longer without cycling on and off. But when the truck is on the road it didn't work for me at all. I have to assume that it isn't compatible with the Dutch Aire.

Turning the Fridge Defend off, I have now run the fridge for months and it works great, better than the original Norcold. So for me, the Fridge Defend was a complete waste of money.


Again, it may work correctly on Norcold and Dometic systems.


Joe & Evelyn


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Posted: 11/15/22 11:30am Link  |  Quote  |  Print  |  Notify Moderator

Joe417 wrote:

My experience with the Fridge Defend has not been a positive one and I always level the rig. It may work fine on a Norcold or Dometic system but does work for me on a Dutch Aire cooling unit with a Norcold control board.

What we experienced with the Fridge defend is that when it is cutting on and off (I think it is about a 20 minute cycle) it did not maintain adequate cooling. As set by the manufacturer, it cycled on and off even when level and not moving.

I put in a Dutch Aire cooling unit and a Fridge Defend last year. The fridge works great as long as I don't turn on the Fridge Defend. When I do, it turns the system off and on causing the system to go above 45 degrees. I texted back and forth with the manufacturer/creator of the Fridge Defend and was told that the Dutch Aire does run at a higher temp than others. He didn't give me any info on what to put the settings on for the Dutch Aire unit. His final statement was that the cooling unit is bad.

While in my drive way and perfectly level, I was able to change some of the setting on the Fridge Defend and get it to run longer without cycling on and off. But when the truck is on the road it didn't work for me at all. I have to assume that it isn't compatible with the Dutch Aire.

Turning the Fridge Defend off, I have now run the fridge for months and it works great, better than the original Norcold. So for me, the Fridge Defend was a complete waste of money.


Again, it may work correctly on Norcold and Dometic systems.


When googling Dutch Aire cooling unit I see that this is the same as the Amish cooling units (which seem to operate very well...I installed one in one of my RVs). From the Fridge Defend videos, it looks like the 1st high temp shutoff occurs slightly above the normal operating temperature of a Dometic/Norcold cooling unit (~180*C). If the normal operating boiler temp of the Dutch Aire/Amish cooling unit is higher for some reason (...even just 5-10*C higher) then it seems like it would trigger the Fridge Defend temp sensor and cycle the fridge off. Obviously, if the cooling unit cannot stay on at it's normal operating temperature uninterrupted then cooling performance would be heavily impacted.

I would guess the Fridge Defend is designed such that you can adjust those temperature settings for detecting high temp (ie. If out of level by more than 3%/6%) so that your Dutch Aire cooling unit is allowed to operate normally (and only shut it off if the temps get higher). From their videos, it looks like normal boiler operation is around 180*C and Danger Zone temps are at ~225*C. The default setting on the Fridge Defend might be somewhere around 185*C. If you could adjust that to 190*C or even 200*C it seems like it should operate correctly with your cooling unit. I'm not an expert, but that seems logical.

-Chris

dougrainer

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Posted: 11/15/22 12:14pm Link  |  Quote  |  Print  |  Notify Moderator

S-J-Chris. Are you an Engineer? Also, when commenting on temps in the USA, use Fahrenheit, not Celsius. 99% of people do not want to figure out C to F. That said, the normal operating range is about 350 to 400 degrees F. The TRIP temp of the Norcold recall box is about 750 degrees. The trip temp of the Norcold and Dometic temp disc is about 800 degrees.

As to off level. People forget all those times when traveling they stopped for a few hours to sight see or eat and those times start to add up. Rarely when pulling over will you be level for safe operation. Doug

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Posted: 11/15/22 04:25pm Link  |  Quote  |  Print  |  Notify Moderator

dougrainer wrote:

S-J-Chris. Are you an Engineer? Also, when commenting on temps in the USA, use Fahrenheit, not Celsius. 99% of people do not want to figure out C to F. That said, the normal operating range is about 350 to 400 degrees F. The TRIP temp of the Norcold recall box is about 750 degrees. The trip temp of the Norcold and Dometic temp disc is about 800 degrees.
Doug


I do have a background in engineering (computers). Probably not too helpful in figuring out mechanical/chemical systems, but helpful for logically trying to analyze things...

For reference:
180*C = 356*F
190*C = 374*F
200*C - 392*F
220*C = 428*F

It seems to be (based on what I have read online, not based on anything I have measured yet myself) that normal, LEVEL operation boiler temps are usually in the 180*C-190*C range (~350*F-374*F).

I am surprised/stunned (anyone else??) that Norcold and Dometic have a trip point sensor/disk that doesn't do anything until 750-800*F. That is insanely hot given normal temps are in the 350*F-375*F range. I wonder what their rationale is for this, and why they didn't make it something like 500*F or 550*F. Anyone know? Once the boiler temps get all the way up to 750*F-800*F internal water has boiled, rust preventative solution has started to crystalize, system pressure must be through the roof....damage is being done. I guess this is the reason for a DIY thermostat (or Fridge Defend) as these can be programmed to turn off the refrigerator as soon as temps get above say 410*F and before overheating damage is being done. Makes sense to me.

dougrainer wrote:


As to off level. People forget all those times when traveling they stopped for a few hours to sight see or eat and those times start to add up. Rarely when pulling over will you be level for safe operation. Doug


I agree, and disagree. Also, driving up a long steep grade will put the refrigerator at a tilt, sometimes beyond the 3 degrees/6 degrees recommendation threshold from Norcold and Dometic. BUT, it sounds like 3 degrees side to side and 6 degrees front to back (relative to the refrigerator, not the RV) is a pretty significant tilt. I saw someone else calculate that 3 degrees came out to a 5 inch difference over 8 feet. So, if your refrigerator is mounted against a side wall of the RV, and your RV was 30' long, in order for you to be 3 degrees tilted side to side (refrigerator), the front of your RV would need to be about 18.5 inches higher (or lower) than the back of your RV. And front to back (refrigerator) 6 degree tilt you would need to be 10 inches higher on one side of your RV compared to the other. That seems like a pretty significant tilt. In contrast, almost every time I've pulled into a camping spot and I've wanted to level my RV, I have been able to do it with just a few of the yellow leveling legos with maybe a maximum of 3-5 inches of lift needed on a couple of the wheels (meaning that even if I had done nothing the refrigerator would have been "level enough" to work and within the 3 degree / 6 degree requirement.

dougrainer wrote:


Rarely when pulling over will you be level for safe operation. Doug


I disagree. I think a huge percentage of the time when you pull over and park it will be well within the 3 degree / 6 degree spec. Sometimes yes it might be off level more than 3 degrees / 6 degrees, but rarely.

Regardless of all the above, If a thermostat is installed on the boiler such that it shuts the refrigerator down if it gets too far above "normal boiler temps" and it can keep the boiler from going over 220*C (428*F) then it seems like it can do a pretty good job keeping the refrigerator cooling unit from getting damaged due to overheating, which can cause leaks, rupture, cooling unit death, and maybe a fire.

I'm not really overly concerned with this. I think I'm just addicted to tinkering with and adding modifications/upgrades to my RVs (especially safety). This would fall into the safety and preventative maintenance category and seems easy enough to do and cheap enough. I purchased the parts (less than $25). When I install it I will post an update.

-Chris

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Posted: 11/16/22 09:06am Link  |  Quote  |  Print  |  Notify Moderator

Chris, My comments come from 43 years as a RV technician. ALL are solid based on MY travels and what I have seen about RVer parked at roadside areas and eateries and even in neighborhoods. TRAVELING on slopes and inclines does NOT cause an out of level problem as the movement overcomes the problem of the Ammonia system. The overheat disc is a SAFETY install. Has nothing to do with stopping a potential blocking problem. IF the out of level or even a large blockage happens, running the Refer, can cause a burst of a cooling unit at its weakest points. IF on LP, the flame can ignite the spewing ammonia and cause a fire. So after lawyers sued Dometic and Norcold 25 years ago, both installed overheat disc's. There was a massive recall over 20 years ago for millions of refers to have the overheat kits installed. ALL new refers since then had the kits installed at build. Doug

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