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Old 06-20-2013, 03:07 AM   #169
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Just got to our destination. Fridge is a perfect 40 degrees. Good nite everybody.
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Old 06-20-2013, 09:15 AM   #170
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Ok so was this what was wrong with your old unit as well?

Perry
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Old 06-20-2013, 10:12 AM   #171
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So how did you limit the cooling, turn off the fan? Block some of the lower vents?

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Old 06-20-2013, 03:16 PM   #172
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Yes, I put in a piece if thin MDF in the lower access door to block the full force of wind from passing through. It still lets some through and it seems that was all that was needed. I do believe that this could have been the problem with the old cooling unit but will never know for sure. All I do know is the rebuilt unit I installed was acting the same as the old unit until I took the corrective action.
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Old 06-20-2013, 09:15 PM   #173
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Expensive lesson. Keep the old unit. I.was having trouble believing that the old unit worked fine standing still and did not work while moving. Did you change the venting at some point?

Perry
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Old 06-21-2013, 12:02 AM   #174
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Expensive lesson. Keep the old unit. I.was having trouble believing that the old unit worked fine standing still and did not work while moving. Did you change the venting at some point?

Perry
No, I am going to send it back. I'll get $100 for the return. I don't need one more piece of junk in my garage. Yes, it is probably a perfectly good unit and it was an expensive lesson but I would not have learned it had I not done what I did. I would have thought the new unit failed or of questionable quality and I would have been wrong. I really learned a big lesson on these units and I hope I can impart knowledge on to others on this cycle.
I am going to develop a training lecture for next years International Rally and help others with their fridge knowledge.
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Old 06-21-2013, 12:08 PM   #175
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Its hard to imagine too much cooling air could do this because most or us are trying to figure out how to install fans etc to get more air flowing to the vent. So ambient 70 degree air on your trip was able to cool the vertical tube that has the insulated aluminum covering enough to do this? What happens when the temperatures are in the 40s? Maybe we should block our vent door somewhat.

I"m glad you problem is resolved.

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Old 06-22-2013, 10:14 AM   #176
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My 30+ year old RM100 cools fine with no fans.

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Old 06-23-2013, 11:00 PM   #177
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Its hard to imagine too much cooling air could do this because most or us are trying to figure out how to install fans etc. to get more air flowing to the vent. So ambient 70 degree air on your trip was able to cool the vertical tube that has the insulated aluminium covering enough to do this? What happens when the temperatures are in the 40s? Maybe we should block our vent door somewhat.

I"m glad you problem is resolved.

Kelvin
I know its hard to imagine, but it is the truth. With enough air flow,or really for that matter, enough cooling effect, you can cool all of that piping between the boiler outlet and the inlet to the condenser fins. You can cool it enough that the ammonia condenses to a liquid before it ever gets TO the condenser. And if it cools prematurely, it will turn into a liquid and fall back down never performing any cooling in the fridge, but cooling the weak ammonia solution in the boiler. Basically, the cycle extends only to the boiler and moisture separator sections and never really reaches the condenser fins and therefore is never turned to liquid ammonia for the freezer and fridge to use for cooling. In short, it can cool everything off right at the boiler. That condenser section is really a point of no return - if it condenses before that part, it will do no work in the fridge. But if it condenses properly IN that section, all that ammonia will cool the freezer and fridge sections as it should.

Allowing less airflow means that cooling of the moisture separator sections is minimised and therefore ammonia condensing takes place in the condenser, where it belongs and it does not cool prematurely in the moisture separators off the boiler outlet.

Frankly, when the boiler outlet is below 180 degrees with over 350 degrees on thermal input to the boiler, and the vapour going TO the condenser fins is less than 120 degrees, I know that subcooling is probably happening in the moisture separator sections and robbing heat from the boiler (and therefore from the fridge) and I have a less efficient operating fridge. It may work and keep the food cool, but it is using extra gas / electricity to do the job.
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Old 06-24-2013, 09:04 AM   #178
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Howdy Buttercup.

Have you an estimate on the airflow? Is this a volumetric or velocity problem? Would you benefit from shielding an area of tubing from airflow?
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Old 06-24-2013, 12:28 PM   #179
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This is quite a surprise and I'm glad you figured it out. I'm impressed with your thought process at finding the solution and wish I could understand all of it.

So far our fridge ranges from 39˚ (cold morning) to 41˚ (hot day), but has gotten higher on 100˚ days with the fridge side in the sun.

I've thought about adding a fan in the compartment, but haven't. Seems like a fan with a temperature sensor to turn in on and off depending on ambient temperature would be the best way to go.

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Old 06-26-2013, 11:25 AM   #180
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Can't you just put some insulation over the separator?
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Old 06-26-2013, 11:55 AM   #181
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Can't you just put some insulation over the separator?
From reading Buttercup's saga, it strikes me that a key issue is to have lots of air blowing over the cooling parts of the workings. I'm guessing that adding insulation to it could block airflow over the cooling fins.
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Old 06-26-2013, 01:51 PM   #182
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Can't you just put some insulation over the separator?
Actually, I was thinking of doing exactly that, putting some fiberglass wrapping on the piping but then I would have to wonder if that would be advisable. Actually, it is working so well now throttling back on the airflow that I think I won't do much more than monitor. But I wonder what other changes I could make, like variable thermal input.
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