Dometic LP Cooling Issues

[ChuckerF14]

Frankly, not cooling well in either mode.

I have a 27 year old Dometic RM2811. I had the cooling unit replaced in early 2018. Two years later I had to replace the AC heating element due to the holding tube rotting out (go figure; I live in Arizona and don't camp at any beaches). The unit has gotten weaker and weaker over time. Research tells me that the many long slow grades on I-8 headed to San Diego may have been cooking my system and reducing efficiency. Who knew?

I decided to replace the cooling unit myself this time. That went well. The box cooled on AC to below 40 from a standing start in under two hours. Unfortunately, when I switched to LP the box temperature went back up somewhere north of 60 degrees.

The good news is that the unit is sitting out on the floor and I have access to all the temperatures. I also installed the ARP Fridge Defender which protects from overheat and provides a constant readout of boiler and absorber temperatures.

I'll cut to the chase....my beautiful blue LP flame was just not hot enough to make big bubbles. Without big bubbles the pump did not pump. This became obvious when I saw that, when operating on LP, the boiler temperature (normally 165 degrees) was much higher (Fridge Defender shut it down at 231 degrees)....but the water separator temperature (just above the boiler insulation) was 100 degrees colder. When I went back to AC, the boiler temperature went down and the separator temperature went up. That was a head-scratcher.

What was happening was that the pump was not pushing solution up to the water separator. The boiler was simmering instead of boiling and the temperature in the water separator never got above 150 degrees. When the pump is pumping properly (on AC at this point), the water separator gets as high as 280 degrees.

So what was the problem? I measured the LP pressure at 11.5" when installed in the coach. I was testing the system with a 5-gallon bottle that put out 13". Pressure was not the problem. I cleaned the LP filter (this one is foam rubber), and soaked the orifice in carburetor cleaner overnight. I also rinsed it in alcohol and blew it out with compressed air. I still could not get enough heat to pump. I looked online and called around for a new orifice. I'd sooner find hen's teeth! Desperate, I dipped the orifice in acetone repeatedly for about ten minutes. Each time I would dip the orifice I would remove it and blow it out from the rear. With a magnifying glass, I could see the opening slowly growing. When I reinstalled the orifice and lit the fire, I could now hear a gentle 'roar' not before experienced. Not like my water heater roar...but an audible flame.

Low and behold, my pump now pumps and my system cools on LP.

Lessons learned:

1. If it pumps, it cools. How well it cools depends on air circulation behind the unit.

2. If it does not pump it dies. Whenever the unit failed to pump, the boiler temperature climbed steadily until the Fridge Defender shut it down.

Hope somebody finds some value in my adventure. All the best!

[MrMark52]

Interesting report - Thanks!

[Old-Biscuit]

Orifice should be soaked in Alcohol and then very low air pressure to dry

Dometic uses a mineral insert that is metered....high air pressure can damage that membrane
*#53 Propane Jet...2007419191
Might still be available at:
https://rvpartsexpress.com/product/d...7419191-jet53/

25 yrs of 'gunk' built up clogging foam filter AND orifice opening
*surprised flame even lit

Burner area 'housekeeping' should be a yearly routine which should also include the flue/flue baffle....it transfers radiant heat generated by flame to perk tune
AC Element transfers by conduction to perk tube

[ChuckerF14]

Originally Posted by Old-Biscuit

Orifice should be soaked in Alcohol and then very low air pressure to dry

Dometic uses a mineral insert that is metered....high air pressure can damage that membrane
*#53 Propane Jet...2007419191
Might still be available at:
https://rvpartsexpress.com/product/d...7419191-jet53/

25 yrs of 'gunk' built up clogging foam filter AND orifice opening
*surprised flame even lit

Burner area 'housekeeping' should be a yearly routine which should also include the flue/flue baffle....it transfers radiant heat generated by flame to perk tune
AC Element transfers by conduction to perk tube

Will the #53 put out 1500 Btu's like the #58?

[Old-Biscuit]

#53 ----original orifice is Larger then #58

(higher the number....smaller the orifice size)

[Fridge Defend]

Originally Posted by Old-Biscuit

#53 ----original orifice is Larger then #58

(higher the number....smaller the orifice size)

Please see this post:

Quality of Heat

Say, I see you and Old Biscuit are both in the Navy?
I make this assumption based on your user name F14, I am assuming this is the legendary Grumman F-14 Tomcat?

Do you have any comments about boiler control in ships?

Thank you gentlemen for serving our nation

[ChuckerF14]

Originally Posted by Fridge Defend

Please see this post:

Quality of Heat

Say, I see you and Old Biscuit are both in the Navy?
I make this assumption based on your user name F14, I am assuming this is the legendary Grumman F-14 Tomcat?

Do you have any comments about boiler control in ships?

Thank you gentlemen for serving our nation

Guilty as charged! Carried the card for 30 years.

We call these things boilers because they boil liquid...but these absorption boilers are distinctly different from ship's boilers. I say that because of the pumping action and the location where the work is performed.

A ship's boiler has pumps that move the condensate back into the boiler and provide back pressure to allow the steam to do work. Without condensate pumps, the boiler pressure would create pressure in both directions and the steam would have nothing to push against (imagine trying to push a truck across a frozen lake...no traction). As you well know, absorption refrigerators have no mechanical pumps....just the ammonia bubbles in the bubble pump and the head pressure from the fluid in the absorption tank.

The other difference is that the absorption refrigerator uses two thermodynamic cycles as opposed to the single-cycle of a ship's boiler. On the ship we heat the fluid in the boiler and chill it in the condenser. All the work is done between the two. In the refrigerator, we heat the fluid in the boiler, over chill the fluid/gas in the condenser, then reheat the fluid/gas in the evaporator. Ship's have evaporators as well...but they are used to distill water for the boiler and the crew. Heat for the evaporators is extracted between the boiler and the condenser. The absorption refrigerator working fluid receives heat in the evaporator where the ship's working fluid gives up heat in the evaporator.

Let me summarize: Both systems have similar components with the exception of the mechanical pumps in a ship's system. They both have boilers, condensers, and evaporators. In a ship's system, all the work is done between the boiler and the condenser...the turbines and evaporators are between the two. In our refrigeration system, the evaporator comes after the condenser. All the work is done after the condenser and before the boiler.

Here is another interesting tidbit from my adventure with the clogged orifice. If I ran on LP long enough to start overheating....then switched to AC (which normally works fine) the unit would just keep cooking off. Apparently, because I didn't have enough heat to make pumping bubbles, I would simmer off all of the ammonia without moving any water to recombine in the absorber. Once the boiler was starved of ammonia, the unit could not pump no matter how much heat was applied.

But now I am preaching to the choir....

All the best,

Chucker

[Fridge Defend]

Originally Posted by ChuckerF14

Guilty as charged! Carried the card for 30 years.

1) We call these things boilers because they boil liquid...but these absorption boilers are distinctly different from ship's boilers. I say that because of the pumping action and the location where the work is performed.

2) A ship's boiler has pumps that move the condensate back into the boiler and provide back pressure to allow the steam to do work.

3) Without condensate pumps, the boiler pressure would create pressure in both directions and the steam would have nothing to push against (imagine trying to push a truck across a frozen lake...no traction). As you well know, absorption refrigerators have no mechanical pumps....just the ammonia bubbles in the bubble pump and the head pressure from the fluid in the absorption tank.

4) The other difference is that the absorption refrigerator uses two thermodynamic cycles as opposed to the single-cycle of a ship's boiler. On the ship we heat the fluid in the boiler and chill it in the condenser. All the work is done between the two.

5) In the refrigerator, we heat the fluid in the boiler, over chill the fluid/gas in the condenser, then reheat the fluid/gas in the evaporator. Ship's have evaporators as well...but they are used to distill water for the boiler and the crew. Heat for the evaporators is extracted between the boiler and the condenser. The absorption refrigerator working fluid receives heat in the evaporator where the ship's working fluid gives up heat in the evaporator.

6) Let me summarize: Both systems have similar components with the exception of the mechanical pumps in a ship's system. They both have boilers, condensers, and evaporators. In a ship's system, all the work is done between the boiler and the condenser...the turbines and evaporators are between the two. In our refrigeration system, the evaporator comes after the condenser. All the work is done after the condenser and before the boiler.

7) Here is another interesting tidbit from my adventure with the clogged orifice. If I ran on LP long enough to start overheating....then switched to AC (which normally works fine) the unit would just keep cooking off. Apparently, because I didn't have enough heat to make pumping bubbles, I would simmer off all of the ammonia without moving any water to recombine in the absorber. Once the boiler was starved of ammonia, the unit could not pump no matter how much heat was applied.

But now I am preaching to the choir....

All the best,

Chucker

1) Good on you The absorption refrigeration unit, although a boiler, is a distillation process. There is a distillate and a solvent , respectively ammonia and water.

2) I am impressed Your training allows you to use the correct word "work". The work of one boiler is the locomotion of a vessel, the boiler in the fridge is not only the locomotion of the working fluids, but the end result refrigeration.

FYI: This is what our automatic control does, it detects when the fluids are not moving in the cooling unit, see our patent.

3) Have you been reading our website, or did you figure this out on your own? You are absolutely correct, did you ever stop to think that the head pressure lowers when the cooling unit is off level? Or when the cooling unit overheats?

4) Slight correction, the terminology is endothermic and exothermic processes.

The boiler and evaporator in the fridge require the absorption of heat.

The condenser and absorber coils require by the release of heat.

6) Now this really meets the iRV2 mission statement
I am learning myself, but I never flew an F-14, and it is my understanding that they do not let just anyone fly one of these beautiful birds! Can I call it a bird, well war bird is correct?

7) Well my teaching is working, my philosophy is that smart folks like yourself helps others understand the truth, which is the science behind our product.

I guess you would have never got off the ground if you paid any attention to the naysayers.

Question, I think it would be supper scary to land an F4U Corsair on a carrier deck. I do not know much, but with a triple wasp to see around, I would imagine not much of the flight deck can be seen on landing.

Thanks for your service to our nation!

I grew up with folks coming back in different states of battel damage,
cannot say I have had to face anything like that, just other stuff life tosses at you

[ChuckerF14]

Originally Posted by Fridge Defend

1) Good on you The absorption refrigeration unit, although a boiler, is a distillation process. There is a distillate and a solvent , respectively ammonia and water.

2) I am impressed Your training allows you to use the correct word "work". The work of one boiler is the locomotion of a vessel, the boiler in the fridge is not only the locomotion of the working fluids, but the end result refrigeration.

FYI: This is what our automatic control does, it detects when the fluids are not moving in the cooling unit, see our patent.

3) Have you been reading our website, or did you figure this out on your own? You are absolutely correct, did you ever stop to think that the head pressure lowers when the cooling unit is off level? Or when the cooling unit overheats?

4) Slight correction, the terminology is endothermic and exothermic processes.

The boiler and evaporator in the fridge require the absorption of heat.

The condenser and absorber coils require by the release of heat.

6) Now this really meets the iRV2 mission statement
I am learning myself, but I never flew an F-14, and it is my understanding that they do not let just anyone fly one of these beautiful birds! Can I call it a bird, well war bird is correct?

7) Well my teaching is working, my philosophy is that smart folks like yourself helps others understand the truth, which is the science behind our product.

I guess you would have never got off the ground if you paid any attention to the naysayers.

Question, I think it would be supper scary to land an F4U Corsair on a carrier deck. I do not know much, but with a triple wasp to see around, I would imagine not much of the flight deck can be seen on landing.

Thanks for your service to our nation!

I grew up with folks coming back in different states of battel damage,
cannot say I have had to face anything like that, just other stuff life tosses at you

Thanks for the details and clarifications. This has been quite an education. I just put a new head gasket on my Cummins 5.9L 12V diesel and absolutely fell in love with that engine as I took it apart (I also went in and fixed the 'killer dowel pin' upgraded my injector pump governor springs, upgraded the fuel plate, and upgraded the injectors). I am having a similar experience with this 27yo refrigerator. It's nice to understand rather than stare and wonder.

For the life of me, I can't understand why any absorption refrigerator ships without the Fridge Defend or similar protection. The pumping process is too fragile and the consequences are too dire. Imagine the economy of scale if every Dometic and Norcold shipped with this technology. With a license, they could build your technology right into the board and deliver safety at minimal cost.

Landing the Corsair (F4-U) aboard a carrier is likely a frightening experience...except you'd be too busy to be frightened. Put me in, coach!

All the best,

Chucker

[Fridge Defend]

Originally Posted by ChuckerF14

Thanks for the details and clarifications. This has been quite an education. I just put a new head gasket on my Cummins 5.9L 12V diesel and absolutely fell in love with that engine as I took it apart (I also went in and fixed the 'killer dowel pin' upgraded my injector pump governor springs, upgraded the fuel plate, and upgraded the injectors). I am having a similar experience with this 27yo refrigerator. It's nice to understand rather than stare and wonder.

For the life of me, I can't understand why any absorption refrigerator ships without the Fridge Defend or similar protection. The pumping process is too fragile and the consequences are too dire. Imagine the economy of scale if every Dometic and Norcold shipped with this technology. With a license, they could build your technology right into the board and deliver safety at minimal cost.

Landing the Corsair (F4-U) aboard a carrier is likely a frightening experience...except you'd be too busy to be frightened. Put me in, coach!

All the best,

Chucker

Thanks for your positive input, have you seen this post:

Another RV Fridge Fire

I am interested in your comments, some on this website feel that:

"Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts" may read:

Being rude and no manners, while disseminating thoughtlessness is what people are here for?

I do not know about you, I am here for the education.
Yes, I learn from everyone!
I am not so filled with hubris as to think that just anyone can fly an F-14.

I was watching a Pilatus doing touch and go's at our local airport.
I thought of the comment I read about the Corsair (F4-U), the engine had so much torque that if one gunned the engine it could flip the aircraft on take off. I cannot imagine doing a touch and go's on an aircraft carrier deck

Thanks for your input on safety, did the Navy teach you to ignore safety or promote it? To say that education was not needed to keep everyone on board safe?

[ChuckerF14]

We love to say that safety comes first. I think Ford's motto was "Safety is Job One." I always chuckle at those sort of slogans. If safety is all that matters then stay home in your bed! If you have a mission to perform, then there are risks involved and you will need to trade a little safety to get the job done.

That said, the military uses the concept of risk management. Risk management calls you to identify and minimize the risks taken to accomplish the task. It also requires you to weigh the risk against the value of the mission and make a final decision to go (when the mission outweighs the risk) or not go (when the risk outweighs the mission).

You weight the risk and reward by multiplying their impact (good or bad) by their probability of occurrence (bad things don't always happen and missions don't always succeed). Driving down the road carries the risk of a fatal collision. The probability of that fatal collision is very low. Therefore, the value of being able to eat tonight outweighs the risk of driving to the market. Driving around on the freeways of Los Angeles because you just want to get out of the house might not meet that threshold. The value of your mission is lower and the risk is greater. That is the core concept of Risk Management.

Applying this concept to RV refrigeration, driving down the road with a significant heat source in a box of combustibles carries some risk. However, we want to camp and we want to keep our food cold. The first step is to eliminate or minimize the risk. A heat pump type refrigeration system would greatly reduce that risk. The cost is fairly high to make that conversion and it might eliminate your ability to camp the way you wish to camp....but it is an option. The Fridge Defend is another option. The Fridge Defend system greatly reduces the risk, costs a fraction of what it would cost to replace an absorption refrigerator, and does not eliminate the option of longer stays away from electricity.

The only benefit to not installing a safety device on your unit is the money you save. I don't think the the cash you save will be much comfort parked alongside the highway waiting for someone to come extinguish your burning rig, or returning from Wendy's to find the pile of rubble in that photo...especially if your pet stayed home to watch the coach.

Everyone's resources and missions are different. Everyone is their own commanding officer. Every commanding officer has to weigh the risks and benefits before making that decision to go or not go. Simply turning your back on the risks and hoping that fate will not find you is no way to lead your team.

Just my two cents,

Chucker

[MrMark52]

Originally Posted by ChuckerF14

We love to say that safety comes first. I think Ford's motto was "Safety is Job One." I always chuckle at those sort of slogans. If safety is all that matters then stay home in your bed! If you have a mission to perform, then there are risks involved and you will need to trade a little safety to get the job done.

That said, the military uses the concept of risk management. Risk management calls you to identify and minimize the risks taken to accomplish the task. It also requires you to weigh the risk against the value of the mission and make a final decision to go (when the mission outweighs the risk) or not go (when the risk outweighs the mission).

You weight the risk and reward by multiplying their impact (good or bad) by their probability of occurrence (bad things don't always happen and missions don't always succeed). Driving down the road carries the risk of a fatal collision. The probability of that fatal collision is very low. Therefore, the value of being able to eat tonight outweighs the risk of driving to the market. Driving around on the freeways of Los Angeles because you just want to get out of the house might not meet that threshold. The value of your mission is lower and the risk is greater. That is the core concept of Risk Management.

Applying this concept to RV refrigeration, driving down the road with a significant heat source in a box of combustibles carries some risk. However, we want to camp and we want to keep our food cold. The first step is to eliminate or minimize the risk. A heat pump type refrigeration system would greatly reduce that risk. The cost is fairly high to make that conversion and it might eliminate your ability to camp the way you wish to camp....but it is an option. The Fridge Defend is another option. The Fridge Defend system greatly reduces the risk, costs a fraction of what it would cost to replace an absorption refrigerator, and does not eliminate the option of longer stays away from electricity.

The only benefit to not installing a safety device on your unit is the money you save. I don't think the the cash you save will be much comfort parked alongside the highway waiting for someone to come extinguish your burning rig, or returning from Wendy's to find the pile of rubble in that photo...especially if your pet stayed home to watch the coach.

Everyone's resources and missions are different. Everyone is their own commanding officer. Every commanding officer has to weigh the risks and benefits before making that decision to go or not go. Simply turning your back on the risks and hoping that fate will not find you is no way to lead your team.

Just my two cents,

Chucker

Well written!