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Old 07-31-2014, 02:34 PM   #1
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Join Date: Jun 2014
Location: Box Elder, South Dakota
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Refrigerator Operation & Fixes


I'm slightly confused and hope you all can straighten me out. There's been a lot of discussion of refrigerators lately which makes me think, and it hurts. My take on refrigerator function is as follows. I'd appreciate any feedback.

There is a thermistor which senses temperature on, or very near, the aluminum fins in the main section (main section as opposed to freezer section). This feeds a controller board that cycles the burner or heater on and off to maintain 'fridge temperature. There will be a dead band so the burner/heater doesn't cycle rapidly. i.e. to maintain 38F the controller might turn the burner/heater on at 39F and keep it on till the temperature drops to 37F. Thus, the temperature at the thermistor is controlled within a tight band. I believe the numbered control knob on the refrigerator adjusts this temperature up and down. (Ours is the Dometic 5.0 cf with an actual knob.)

When the burner/heater is on the ammonia cycle does its magic and cools the aluminum fins in the main section and an aluminum plate in the freezer. The cycle operates the same whether the heat comes from the propane burner or the electrical heating element.

So what can go wrong, besides a truly broken 'fridge?

First, the thermistor may not represent the temperature of the main section. The temperature near, or at, the fins may well be colder than the rest of the main compartment. I'd suspect a symptom will be a variation in main section temp. with changes in outside temperature. If more cooling is required (higher outside temp.) the fins will be cooler, the thermistor just right, but the main compartment will have higher temperatures than desired. i.e. How much does a thermometer in the 'fridge rise when the outside temperature varies from 50F to say 70F?

I see three ways to help this problem. 1. Circulate the air within the main section. Some are doing this with battery fans or 12v fans placed right over the fins. 2. Move the thermistor to a more representative location within the main box. (Anyone know why they put the thermistor at the fins?) 3. Add insulation around the refrigerator. This would slow the heat transfer and tend to maintain a more consistent temperature.

The second major problem is lack of cooling at high outside temperatures. It takes more effort to push heat out of the 'fridge the higher the temperature you're pushing that heat to becomes. This is an indication that the cooling unit, as configured, isn't up to the task. The cooling unit depends on a flow of air over its coils to lower the temperature of air in contact with those coils. Air flows in at the lower 'fridge vent and out the top. Since the 'fridge is pushing heat to the air, thus raising its temp., there will tend to be a natural flow up the back of the 'fridge. An upper roof vent should work better than a upper side vent.

We can improve performance of the cooling unit in a couple of ways. 1. Make the flow over the cooling unit as efficient as possible. I think following Dometic's installation directions is a good start. This is where the baffles come in. 2. Increase the flow actively using fans. I'm not sure where to best place these, at the upper exhaust vent, at the lower intake vent, or in the middle of the column. Dometic seems to suggest a fan at the exhaust vent for our wall vented 5 cf 'fridge. 3. An awning or similar to shade the side of the trailer where the 'fridge is located, or park in the shade. 4. Increase the insulation around the 'fridge. This will lower the overall work the cooling unit has to do.

So, if the problem is varying temperatures within the main section the first set of fixes are most appropriate. If the problem is overall cooling at high temperatures the second set of fixes should help.

One other problem is possible. When the outside temp. is very low the main compartment is fine but the freezer doesn't freeze. I believe the freezer is not controller. Dometic has sized plates in the freezer and main section so if the main compartment is OK then the freezer will be below freezing. This seems to work well till the outside temperature becomes very low. In this case the main compartment can be maintained with very little cooling. With little cooling the freezer will warm, in the extreme approaching the temperature of the main section. I've heard one solution is to put a small heater in the main compartment to force some cooling. A small incandescent light was suggested.

If you're still reading, thanks. It turned into a long post. But since you're still with me: Does this make any sense? Where are the errors in my thinking? Does it match anyones experience? I'd be particularly interested in your experiences that back up, or refute, these theories.


P.S. I took our 2011 Escape 19 on a short two day trip just to check out the 'fridge. We had some trouble on the way to Bandon but then it cooled down, the weather and the 'fridge. Over the two days I tried both propane and 120V AC operation. It worked very well and I'd be real happy if it continued this way. Our 'fridge is the 5 cf unit, I believe a RM2510. Outside temperatures varied between about 55F and 95F. The site was partly shaded. There may be some issues with propane on the road, i.e. wind disturbing the heating, but that will take a lot longer drive to evaluate. After this trial I'm less concerned, time will tell.

Hugh Currin
2011 Escape 19
2018 RAM 2500 Diesel
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Old 07-31-2014, 03:05 PM   #2
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Trailer: 2012 Escape 19'
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Hugh, great post! From what I've read, the 5.0 units seem to work pretty good but the new 8551; 4.3 unit and the 8555; 6.7 unit both seem to have cooling problems at higher ambient temps. Mine is a 4.3 and works fine until it gets up around 90f.

I've been looking at the water cooling systems used in high end gaming computers and wonder if a water-cooled evaporator coil would be very efficient. A small water circulating system would be pretty simple to retrofit to a heatsink attached to those coils...just wondering...:

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Old 07-31-2014, 03:37 PM   #3
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Originally Posted by currinh View Post
Does this make any sense? Where are the errors in my thinking? Does it match anyones experience?
Absolutely! An excellent summary of the situation.

I have experienced the problem of a warm freezer in cold outside conditions, and concluded that it had the cause which you describe.
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