New Fridge Topic: A Different Approach

[rbryan4]

Ah, Dometic IS continuous cycle:

RV Products - DometicUSA

[escape artist]

Originally Posted by Klem

Put an ear by the lower refer vent and you should hear the burner when it's 'on'. And/or open the vent and you'll see a flame peep hole.

Careful ... you don't want to burn up the burner

Hi: Klem... So far I've used 120V. to power the 6.7 refer. It's cool today but with the thermistor in position shown in pic. the temp on 2 bars was 37*F. before opening the door twice and taking the pic. SWEET!!! Alf
escape artist N.S. of Lake Erie

[Patandlinda]

Can someone tell us what the thermistor does ?

[Parker]

They are a sensor designed to provide a signal to the control circuit that is attempting to maintain the desired fridge temp. Their resistance is roughly proportional to temperature, so if the fridge temp goes up, the resulting increased resistance of the thermistor provides a signal to the control circuit to increase cooling.

As Alf moves his thermistor to a warmer spot in the fridge, he is fooling the control circuit into providing more cooling for whatever setting he has chosen on the control panel. I still maintain that there is no magic additional cooling available. When the outside temps get too warm, his fridge will be just as limited as it was before. But Alf wants to find that out for himself.

[escape artist]

Hi: Parker... No "Fooling" an old fool!!! I feel that where the thermistor is now located is more representative of the average temp in the fridge box. My thermometer is located at the front edge of the shelf, which is warmer than the back. If I get the same reading on 2 bars that I got on 5... then when in Florida temps I should get a favorable reading on 5. If not then I'll join the queue for a new fridge from Dometic under warranty... (Right)?
I'm not ready to poison the arrow, just yet. Alf
escape artist N.S. of Lake Erie

[Brian B-P]

Originally Posted by rbryan4

Good point. There are basically two types - continuous cycle and intermittent cycle. Not sure which one the Dometic is. Here's a pretty good explanation of the differences:

SMALL AMMONIA REFRIGERATOR

Originally Posted by rbryan4

Ah, Dometic IS continuous cycle:

RV Products - DometicUSA

Yes, and consumer absorption refrigerators are likely all continuous. One hint is the inclusion of hydrogen (or helium) in the refrigerant charge, which provides the pressure differential or continuous "pumping" action.

[Brian B-P]

Originally Posted by Parker

As Alf moves his thermistor to a warmer spot in the fridge, he is fooling the control circuit into providing more cooling for whatever setting he has chosen on the control panel. I still maintain that there is no magic additional cooling available. When the outside temps get too warm, his fridge will be just as limited as it was before.

I agree that moving the thermistor doesn't change the total cooling capacity - it just sets a different target for the refrigerator to try to reach. On models with no adjustment in the control circuit (not used by Escape, but included in the Dometic line), this is the only adjustment method available, and is clearly described both in the manual and by a label in the refrigerator interior. The recommended adjustment is only along the height of the fins.

[hotfishtacos]

During the first year I had my 19 I experienced cooling problems and wired a potentiometer across the thermister circuit to fool the system. I was able to make the refer run longer but soon realized that the unit had a problem with cooling capacity in hot weather so, realizing that this wasn't going to address root cause, I pulled the potentiometer out and put everything back to stock.

[grc]

I guess I'll be the one to ask the dumb question.

Right now the debate is between the propane frig and trying to fix it and the 12v compressor frig and how much is enough battery/solar to keep it running. The issue with the propane frig lack of performance seems to be related to the EU Climate Class limitations. I could be wrong but the EU Climate Class info and restrictions looked to apply to all kinds and types of new refrigerators manufactured in Europe.

The dumb question is, if you go with a new EU manufactured 12v compressor frig will that fix the performance problem or will you still be dealing with poor performance due to the Climate Class issue?

[escape artist]

Originally Posted by grc

I guess I'll be the one to ask the dumb question.

Right now the debate is between the propane frig and trying to fix it and the 12v compressor frig and how much is enough battery/solar to keep it running. The issue with the propane frig lack of performance seems to be related to the EU Climate Class limitations. I could be wrong but the EU Climate Class info and restrictions looked to apply to all kinds and types of new refrigerators manufactured in Europe.

The dumb question is, if you go with a new EU manufactured 12v compressor frig will that fix the performance problem or will you still be dealing with poor performance due to the Climate Class issue?

Hi: grc...The only dumb question is the one you didn't ask... I believe that with "Global Mfg" the same issues apply to both style of RV Fridges.
To get around the fridge fire issue Dometic in essence turned down the power of the propane boiler. Since these fridges are a continuous cycle my solution was to move the thermistor sensor to a warmer spot in the fridge.
My RVTech told me his solution was to add a spacer to bring the sensor forward from where it was... but that raised the temp. back to 41*F. I elected to put it back where I had it... but I need to figure out a safe mount for it. Alf
escape artist N.S. of Lake Erie

[rbryan4]

Originally Posted by grc

I guess I'll be the one to ask the dumb question.

Right now the debate is between the propane frig and trying to fix it and the 12v compressor frig and how much is enough battery/solar to keep it running. The issue with the propane frig lack of performance seems to be related to the EU Climate Class limitations. I could be wrong but the EU Climate Class info and restrictions looked to apply to all kinds and types of new refrigerators manufactured in Europe.

The dumb question is, if you go with a new EU manufactured 12v compressor frig will that fix the performance problem or will you still be dealing with poor performance due to the Climate Class issue?

Not a dumb question. Let's clarify.
-Climate class ratings are only applicable to fridges that are legally sold in the EU, although they do post them for Australia as well.
-ALL fridges sold in the EU must have a climate class rating, regardless of the fridge type.
- Having a climate class rating doesn't lower the fridge cooling performance, but merely tells you at what ambient temperature range the fridge can be expected to perform normally. So, a T rated fridge performs better than an SN when it's hot out, because it's designed to. It just uses more power.
-There are many compressor based fridges with a Tropical climate class rating - far more than LP/absorption fridges because a compressor provides a superior cooling source, and it's easier to achieve the T rating.
- Absorption fridges don't exist because they're better, but because they provide a means of powering the fridge by a heat source (propane), which makes them suitable for places without electrical power.
- The issue here is several things, but mainly: we need a fridge that fits through a 22" door, one that provides adequate interior capacity, and one that cools in high ambient temperatures.
- If you're talking propane, the Dometic RM85XX series does fit, but because it's an SN rated fridge, it doesn't perform well in high ambient temps.
- The compressor based fridges that I and others have mentioned here as possible suitable replacements are all "tropical" rated or equivalent, and can be expected to perform well, in some cases up to 43 degrees Celsius, or 109 Fahrenheit.
- You'll use more electrical power with higher ambient temps because the compressor runs more frequently.
- A solar solution with a compressor fridge must take all of this into account in order to provide adequate power in high ambient temperatures when the compressor is running frequently or non-stop. If it's cooler, no problem. The small compressor based fridge in my garage (ambient temperature of 88 to 95 degrees in the summer months) only runs about 40% of the time.

[grc]

rbryan4,

Maybe I missed it in the discussion but it would be good to show where you are getting the information saying "Climate class ratings are only applicable to fridges that are legally sold in the EU."

"A compressor provides a superior cooling source"

You would no more put your hand on the compressor discharge pipe of a direct expansion refrigerator (12v or residential) than you would put your hand on the ammonia piping leaving the boiler in an absorption cycle refrigerator (rv propane frig). They are not cool, they will burn you due to the hot gas inside the pipe.

I'm familiar with the Mollier diagram for direct expansion refrigeration less so with Mollier diagram for absorption refrigeration, however they are similar. I was a professional mechanical engineer, retired from Boeing, and actually made a crude working refrigerator many many years ago as part of training. I did that when I was refrigeration certified. Wouldn't try it now.

Anyway, thank you for explaining all this and clarifying what I need to know.

[rbryan4]

Originally Posted by grc

rbryan4,

Maybe I missed it in the discussion but it would be good to show where you are getting the information saying "Climate class ratings are only applicable to fridges that are legally sold in the EU."

"A compressor provides a superior cooling source"

You would no more put your hand on the compressor discharge pipe of a direct expansion refrigerator (12v or residential) than you would put your hand on the ammonia piping leaving the boiler in an absorption cycle refrigerator (rv propane frig). They are not cool, they will burn you due to the hot gas inside the pipe.

I'm familiar with the Mollier diagram for direct expansion refrigeration less so with Mollier diagram for absorption refrigeration, however they are similar. I was a professional mechanical engineer, retired from Boeing, and actually made a crude working refrigerator many many years ago as part of training. I did that when I was refrigeration certified. Wouldn't try it now.

Anyway, thank you for explaining all this and clarifying what I need to know.

Well yeah, they both get hot. My point was that almost all refrigeration applications are compressor based. There's a lot of bang for the buck. Absorption does work but let's face it -- there's a reason why its used in an RV and not a home. It just doesn't work as well.

As for the climate class requirements in the EU, my language may have been inartful. The climate class rating is required to sell a fridge there, but its not required here. If a fridge that's sold in the EU is also sold here, it will have a climate class rating on the label. If you want to read through this mush, there are several sources. Here's one:

http://ec.europa.eu/danmark/document...28_6481_en.pdf

[escape artist]

Hi: rbryan4... Absorption fridges are avail for the home. They are expensive and most Amish homes have one. No need to be connected to the grid with one.
I'm still playing with the location of the thermistor sensor in our 6.7. Wish I could make it 85*F. and sunny out side!!! Alf
escape artist N.S. of Lake Erie

[rbryan4]

Originally Posted by escape artist

Hi: rbryan4... Absorption fridges are avail for the home. They are expensive and most Amish homes have one. No need to be connected to the grid with one.
I'm still playing with the location of the thermistor sensor in our 6.7. Wish I could make it 85*F. and sunny out side!!! Alf
escape artist N.S. of Lake Erie

Cmon down Alf. I've got some 85 degrees I can sell you.

[Vermilye]

I have a friend that has a 1953 kerosene fired absorption refrigerator. Still running!

[rbryan4]

Originally Posted by Vermilye

I have a friend that has a 1953 kerosene fired absorption refrigerator. Still running!

Perhaps another example of "they don't build 'em like they used to."

[grc]

rbryan8,

Please go back and read pages 4 and 5 of this thread. Documents I have posted to this web as sources of information are dated and due to age may have been altered. It is very possible I missed something concerning sales of these refrigerators in the pdf file link I posted on page 5.

In this thread my post#128 links to a 2007 Dometic service manual that uses the word identical describing the RM 8-series cooling unit and the unit it replaces, the 7-xxx generation. While I certainly hope the RM 8-series cooling unit has not been changed or altered since 2007 this seems something Dometic would have to confirm as Climate Class did not appear to exist at that time.

Mr Escape Artist pointed to residential usage ammonia refrigerators by the Amish. They brand they used to use was Servel, but Lehman Brothers has several other brands. Ammonia refrigeration is not just used in small scale, rv's and residential, it is used in large scale commercial food storage and processing, along with massive concrete construction. I was surprised in the mid 1990's that a huge dam project in China, the Three Gorges Dam across the Yangtze River, had contracted with an American firm in Redmond WA for the ammonia refrigeration design to cool the concrete to minimize cracking.

[rbryan4]

Originally Posted by grc

rbryan8,

Please go back and read pages 4 and 5 of this thread. Documents I have posted to this web as sources of information are dated and due to age may have been altered. It is very possible I missed something concerning sales of these refrigerators in the pdf file link I posted on page 5.

In this thread my post#128 links to a 2007 Dometic service manual that uses the word identical describing the RM 8-series cooling unit and the unit it replaces, the 7-xxx generation. While I certainly hope the RM 8-series cooling unit has not been changed or altered since 2007 this seems something Dometic would have to confirm as Climate Class did not appear to exist at that time.

Mr Escape Artist pointed to residential usage ammonia refrigerators by the Amish. They brand they used to use was Servel, but Lehman Brothers has several other brands. Ammonia refrigeration is not just used in small scale, rv's and residential, it is used in large scale commercial food storage and processing, along with massive concrete construction. I was surprised in the mid 1990's that a huge dam project in China, the Three Gorges Dam across the Yangtze River, had contracted with an American firm in Redmond WA for the ammonia refrigeration design to cool the concrete to minimize cracking.

Thanks for the reference. On your comment on those pages:

"My guess for model RML8555 is that it is capable of performing for any of the Climate Classes but the circuit board makes it specific to the Climate Class. "

It may be true that the circuit board is different for different climate classes, but it's not the only thing. The box itself is different for Tropical rated fridges, and is better able to hold in cold air in high ambient temperatures. There may be a number of other differences too. Unfortunately, unless you work for Dometic or Norcold, you aren't privy to the exact differences. Bottom line, the Subnormal climate class rated fridges don't cool adequately when it's hot out, and sometimes even when it's not.

I fully realize that absorption refrigeration has been in use for a long time. It's adoption as the standard for rv refrigeration however, has nothing to do with performance and everything to do with portability and a long lasting fuel source. Side by side, my small compressor based fridge in the garage will outcool any RV absorption based fridge. It'll use alot more energy doing it, but it performs very well, even in 100 degree heat.

Think about it - how many rv forums, threads, comments, etc are all complaining about inadequate cooling in their absorption fridge? You just don't hear the same thing from the marine community who largely uses a DC fridge instead. The problem isn't unique to us -- it's just exacerbated by the fact that the RM85xx series used is designed for subnormal climates.

[escape artist]

Hi: grc... Haven't been called Mr. in a long time. Thanks!!!
As newly weds we used to rent a locker at the local cold storage. It always smelled of ammonia when in there!!! Alf
escape artist N.S. of Lake Erie