Altitude or attitude?

[Civilguy]

Originally Posted by CarlD

Regarding the chimney issue. Once again you stated it works ok on electric. If it is a chimney issue wouldn't it also have reduced performance running on electric at altitude?

From the way Dometic keeps emphasizing the impacts of a dirty flue or baffle on gas operation in this manual, it sounds like the electric element is connected closely enough to the boiler tube to operate by conduction so that the carbon buildup doesn't have a significant impact of the heat transfer in that mode.

The manual (for a RM2663, et al) says (emphasis added):

The flue baffle ( spiral baffle ) is a twisted piece of metal
that hangs in the flue tube to slow the heat from the flame
to the proper location on the cooling unit. If the flue baffle
is too high or low the heat will not be transferred to the
cooling unit properly.

Lack of heat transfer to the cooling unit will cause low cooling
performance in the gas mode. It should be cleaned
periodically, at least once a year. The proper position of
the baffle above the burner should be as shown in the
chart

Carbon build up will not allow the heat transfer to the cooling
unit and cause lack of cooling on gas. The flue tube is
welded to the boiler of the cooling unit. In a rough riding
coach there have been rare cases where the weld will
crack and create lack of cooling. The flue tube must be
cleaned periodically, at least once a year. Clean by using
a flue brush, Dometic Part No. 0151404001.

[Raspy]

The electric element does not deliver its heat in the same way as the fire does. It sits in a well and conducts to the fridge pipe, instead of just having the fridge pipe in the chimney exposed to rising hot exhaust.

Here is a pic of the electric heater out of its well:

[WizWid]

Originally Posted by MyronL

Actually I did, Widge--- post #20. (--Note Indicated at the much lower altitude at the ABQ Home Depot and then over to Cabellas - even lower altitude - Fridge began to cool steadily on propane. Then, leaving it on propane and driving back to 6700 ft home, when I got there it had spiked back up.) ABQ is about as close to sea level as I can get to around here.

OK. I give up. The question was does it work well at sea level on propane. The fact that it gets down to 57 degrees at 5000 feet does not tell me anything.
Thanks for playing though!

[MyronL]

Guessing yes, but of course, it is a calculated, see level drop of 5 degrees, guess.

[Lloyd (aka Santa) Coltman]

You said the propane pressure is good, but was it verified at 11 inches water column? If it works on electric, nothing is wrong with cooler system. These fridges are very critical on propane pressure.

[biw314]

I’ve tried all the classic propane fridge mods with fans inside and out, insulation, baffling, rolling it over, and built a manometer. One thing I learned is that you can’t judge the pressure by the way the flame looks. My manometer was just some plastic tubing attached to some scrap plywood with some scale marks. Getting the pressure right was probably the biggest improvement of all the mods.

[jtweigandt]

a few years ago, we owned a 16 front bunk mid bath. The fridge worked fine at altitude and at home. I made the mistake of pluggin in my unit when it was on a very unlevel driveway, and the electric option kicked in on the fridge, and ruined the unit.

1. It did fit in and out of the spot it was installed in and could just barely squeeze through the door of the scamp

2. I ordered a replacement cooling coil unit from an outfit in Tennessee.. but failed in my attempt to repair..

3. Check the chimney etc.. there are supposed to be baffles if I recall to slow the draft some.. to maximize the heating of the evaporative unit. Ammonia cycle is documented on various web sites, if you need to wrap your head around what you are doing. Also check for bug webs, daubers, paper wasp or any other crap in the chimney.

4. if its an older unit.. look up “burping an rv fridge” Sometimes you can recover from a relative vapor locked condition.

5. Newer units have some sort of overflow or bypass tubing and are less prone to damage from out of level operation.

I ended up selling mine.. discounted by about 1000 bucks because of the fridge as we moved up in size.. Ultimately loved the Scamp, but the Mrs wanted a bed that we didn’t have to crawl over each other, and a stand up potty/shower. Still miss the ease of towing, and the conversations when you pull in somewhere.

[Joe Romas]

Here's what a Dometic 3 way refrigerator at sea level at 97f ambient temperature in a 17' Casita is capable of. For those interested in knowing how visit the Casitaforum and search for a very long thread called how to make the refrigerator work better. It starts out with a refrigerator removed from a brand new, OOPS, it was three years old, Casita not working well at all. Same refrigerator sitting in an open building it worked perfectly. For those interested but not inclined to look for the thread the problem in a nutshell is this. You have a set of coils trying to cool liquid inside them. But at the same time you have the much hotter heat from the propane flame flowing past those coils. The answer is to separate the air flow from the two sources of heat. In Europe where Dometic refrigerators are made they have different vent pieces to do this but are not available here.
The picture is of my wireless remote temperature gauge showing my results on my Dometic refrigerator on propane. Ambient temperature of 97f with refrigerator facing the sun, Freezer temperature of 1.4F and refrigerator 37.5 F. With these results you'll have a problem of things in the refrigerator freezing.

[Marvin P]

We have a Norcold 3 way refrigerator in our trailer, and it does not operate properly on propane when the altitude gets close to 4,000 feet or above. We almost killed our batteries when camping in Colorado last fall.To operate on batteries while towing we had a Redarc BCDC charger installed during the winter; it requires much larger gauge wires coming back from the tow vehicle. The standard 7 way electric trailer connectors do not provide enough power to prevent the batteries from discharging (while using the rrefrigerator on battery power), even while driving. The batteries are getting a much stronger charge now while hooked up with our tow vehicle, even when idling.

[1Oldman]

Originally Posted by MyronL

I live here at an altitude of 6700 feet. Well today there seems to be only two conclusions to be drawn. As a 3-way, the Dometic RM8551 fridge in my trailer is a lemon, or, the fridge is adversely affected by altitude. Or both.

It does work great on shore power and on battery power. On propane? Not!

Have you checked the re-settable heat fuse that is located on the flue pipe in the back of the refrigerator? There are 2 red wires connected to the thermal fuse. Press the button in the center of the thermal fuse and then test for continuity across the two terminals. If this thermal fuse has tripped the unit will not light on propane.

Good luck - Dan

[Mike J. L.]

https://sotooutdoors.com/product/pocket_torch_with_refillable_lighter/

[Aaron Thoroman]

Originally Posted by Raspy

Myron,

I have a friend with a Dometic fridge in their new trailer that would not cool, no matter how long it was left burning. An RV repair shop gave up on it and said it was "defective".

I found out the trailer had been parked on a severe angle at the dealer, with the system running, and after that it would not work. A popular, old fashioned fix for absorption fridges is to turn them upside down for a while, after they have been out of level enough to make them stop cooling. They have to be fairly level, or used while driving.

I suggested something to try before giving up completely, or pulling it out to turn it upside down.

I asked them to start it and leave it running for a while, maybe several hours to get the hot part fully warmed up, and the absorption hot enough to work. And then take it for a drive. During the drive I asked them to be sure and go around lots of corners and over some bumps.

They did this and it fixed it. It is now working normally.

In reading your story, you repeatedly commented how big the flame was. "Robust, turned up to 5 dots, ain't gonna burn any bigger".

I wonder if the flame is too big? The flame doesn't burn bigger to make more cold, it burns longer. Older ones would turn way down when the box was cold and up to make more cold, but that was just so they could stay lit as a pilot light. Small in that case, was a pilot light, big was the working flame. Newer ones go out and then re-light when more cold is needed. But they don't just turn up to a bigger flame to make more cold. Bigger is not necessarily better. Bigger doesn't necessarily equal more cold.

Someone mentioned that they can only go a certain amount colder than ambient, and that might be the problem in your case. It is not the problem. Absorption systems do have their limits, but mine, for instance was 6 degrees F in the freezer compartment today while outside temp was 90. And yours works on 120 volts. So you are not out of its working range.

So, you might have the dreaded bubble problem, that can be solved by driving it around while it is trying to cool. Or you might have too large of a fire that is overwhelming it. The latter is just a theory and I have never seen that happen, but you repeatedly commented how big the fire is. Turn it down. Or restrict it somehow and see if that helps. It is not about giving it more and more fire to get cooler and cooler. All it has to do is boil the ammonia to separate it from the water, and cause hydrogen bubbles to form. The boiling point in the system is probably a little over 100* F.

While it is on, the heat should be getting all through the finned tubing on the rear of it. Compare the temp of the tubing when running on 120 volts, with the temp while running on propane. This will prove that the flame heat is getting into the system and it will show you how much heat is needed to cool the box on 120 volts. Way more heat there from the flame might be the problem.

I don't know who you are Raspy but you are the most intelligent poster I have seen here on Absorption Refrigeration. Everything you have said is 100% correct!

[Eggcentric]

Don't have time to read through all the responses, so I may be duplicating advice someone else has given.
2 things, propane often gets 'diluted' with butane especially in the summer, butane does not vaporize below 32F, not sure what altitude may do to it.

Try putting a 12v muffin fan behind the fridge in such a way that it blows air up through the coils you will find this helps.
Check the air gap between the trailer an coils, should be one inch +/- and just the width of the fridge, builders sometime skip this, you need air flow over the coils.
To get a 17degree temp reduction in a 90 deg trailer is not all that bad, given poor insulation etc.
Take the trailer for a 10 mile drive, it is surprising what that will do for the circulation of the refridgerant.

[Aaron Thoroman]

Originally Posted by Raspy

Myron,

I think you are barking up the wrong tree with the propane issue.

You obviously have the burner working as good as it can, and the flame picture shows a nice clean looking burn. And it had no affect on the outcome. You didn't get a percentage reduction in cooling, you got nothing. Altitude will not just stop it at some magic elevation, it will maybe reduce the performance. The amount of cooling is based on the size of the flame, so it should just reduce cooling and not stop. As an example, we live at 5,000 ft and the fridge works fine. We like to camp at Twin Lakes, which is above 8,500 ft and it works normally there too. My freezer temp a couple of days ago was 6 degrees F. Remember too, the fridge is a closed loop system that is not affected by atmospheric pressure changes. The only reduction in performance I've seen was due to high ambient temps where the system could not get rid of the excessive heat.

And just as an additional note, the compensation made in carburetors on engines, for elevation, do not restore power as seem to be suggested in an earlier post. They correct the mixture. This makes the engine burn correctly and prevents carbon buildup, but it does not add back power lost to elevation, which as a rule of thumb, decreases by about 3% per 1000 ft elevation. Even fuel injection engines that run very well at altitude, lose the same amount of power, based on reduced atmospheric pressure.

You commented that there is no way to adjust the flame. Well, of course there is. You might change the regulator setting, change the jet or deflect some of the heat out of the normal path, to run a test. But either way, the propane system seems to produce no cooling, while the electric works OK. And again, in your case, it is not a percentage change based on elevation, it just doesn't seem to work at all. And your burner seems to be running very well. So I'd say, there is something else wrong. Have you taken the chimney apart to see how it works or if it is blocked? Have mice moved in? Is there any way the heat from the flame is not getting to the right place as it is with the electric heater?

Finally, since it works on electric, it is not being stopped by a bubble, so there is no need to turn it upside down. That is a last ditch effort when all else fails. In your case it does work.

Once again Raspy is right on the money! I could chime in with some ideas but they would be the same ideas! LOL!

[Civilguy]

Originally Posted by Aaron Thoroman

I don't know who you are Raspy but you are the most intelligent poster I have seen here

Oh darn, he just bought a larger hat last month and now that one is going to be too small!

[wilyoung]

Originally Posted by MyronL

I live here at an altitude of 6700 feet. Well today there seems to be only two conclusions to be drawn. As a 3-way, the Dometic RM8551 fridge in my trailer is a lemon, or, the fridge is adversely affected by altitude. Or both.

It does work great on shore power and on battery power. On propane? Not!

Obviously the cooling unit operates properly when it gets enough heat. It doesn't care what the source of heat as long as there is enough. Propane, 120vac, or 12vdc doesn't matter.


With electricity the amount of heat depends on the wattage of the heater unit and using the proper voltage. Neither of which depends on altitude or oxygen content of air.


With propane the amount of heat is determined by the quantity of propane burned and the efficiency with which it is burned.


Some one mentioned carbureted engines and high altitude jets to prevent carbon formation. Not quite all there is to it. I am a pilot of carbureted airplane engines. We have a throttle and mixture control to control the operation of our engines at various altitudes. The ratio of gas to oxygen controls the energy produced by the burning the gas. There is an optimal ratio. Either too much or too little oxygen reduces the energy produced, with other unwanted results as well. At higher altitudes there is,of course, less oxygen per volume of air so to maintain optimal power requires leaning of the mixture (less gas per volume of air). But less gas also produces less power (heat). So non-supercharged engines, even while operating at optimal mixtures, produce less power at altitude than at sea level, period. Something we have to account for in our flight planning.


Same thing with propane. There is an optimal gas/oxygen mixture. Without mixture adjustment at altitude heating efficiency drops. Too much gas, not enough oxygen. Different manufacturers, maybe even different models from the same manufacturer, may have different ways of compensating for altitude differences, but without some sort of variable mixture control none will cover all altitudes.



With just a quick perusal of an on-line Dometic 8 Series Operating Manual I find this, "For physical reasons, gas ignition faults could occur starting from an altitude above sea level of approx. 3280 ft. / 1000 m (No malfunction)." Seems your fridge may not be designed to operate on gas where you are. And even if it does ignite it will not be burning efficiently with enough heat to cool the fridge.


"For physical reasons..." - Not optimal gas/oxygen ratio.

[Eggcentric]

Dunno if anyone else has mentioned this, but if your rig is not very level, the heat from the flame may be going to a spot on the chimney that is not heating the refrigerant.
Would explain why fridge works on electric.

[Len S]

No mention just how old this fridge is but if an older model and if it was ever parked with the fridge operating at an angle the chemical could have baked on the inside and if that is the case it may not be getting enough heat from the propane burner to vaporize the chemical . Newer ones were designed to compensate for angled parking when in use.
Just a thought.

[Raspy]

Originally Posted by Civilguy

Oh darn, he just bought a larger hat last month and now that one is going to be too small!

How did you know I was shopping for a new hat? Mine all seem a bit too small all of a sudden.

[Raspy]

Originally Posted by wilyoung

Obviously the cooling unit operates properly when it gets enough heat. It doesn't care what the source of heat as long as there is enough. Propane, 120vac, or 12vdc doesn't matter.


With electricity the amount of heat depends on the wattage of the heater unit and using the proper voltage. Neither of which depends on altitude or oxygen content of air.

Wil, I agree, but I think you are missing the point.

While heat is heat, let's say BTUs are BTUs, regardless of the fuel used, in this case, the delivery method may be the culprit.

The electric heater conducts heat from the heater well, to the refrigeration pipe directly. The heater, the well and the fridge pipe are all in physical contact. The propane heat is delivered by warm gasses rising past the pipe. If the rising pathway is disrupted, or blocked in some way, the energy may not be getting to the fridge pipe even with the burner burning.

I agree that it doesn't matter what the heat source is, but one method might work while the other does not, even if they are producing the same amount of heat. it certainly does matter how that heat gets to where it needs to be. A rats nest, for instance could stop the fridge from working on gas, but not on electric. And since it works on electric, but not on gas, the differences in the delivery systems becomes interesting.