My Ice Cream Bars Melted!

[fudge_brownie]

For the past several years I have had a love affair with my RMD 8555 Dometic refrigerator. The litany of issues with this refrigerator is too lengthy for this posting, just to say it's more than I would want to wish on anyone.

The RMD 8555 is a 2 door refrigerator with the freezer on top and refrigerator bottom. The single sensor (thermistor) for measuring temperature in the refrigerator is located in the lower portion. This past evening we prepared for a late fall trip, not a common in event. We loaded the refrigerator and freezer last night, the freezer included my favorite ice cream bars. The trailer sat unoccupied and unheated overnight. Overnight lows were in the 26 degree range and we encountered an interesting phenomenon this morning when checking freezer and refrigerator temperatures.

We monitor the refrigerator with a device called SensorPush , it connects to our iPhones and gives us up to the minute temperatures as well as graphs indicating the last hour, past 24 hours or 7 days of data. Looking this morning at the freezer temperatures I noticed it was in the 20 + degree range. I immediately checked to make sure that the freezer door was closed properly. And it was. Why did my ice cream bars melt with the refrigerator compartment remaining at a very constant 36 degrees?

SensorPush gave me some indication of what had occurred. Looking at the graph for the last 24 hours, one could see the temperature fluctuate up and down, as the burner (it was on electric) turned on and off. About midnight the refrigerator temperature started to drop. The opposite happened in the freezer as its temperature started to rise. Going from approximately zero degrees at midnight, until near 22 degrees at 8 AM. Both graphs were even rise or drops in temperature, indicating that the burner did not go off.

It did not need to go off, as the sensor in the refrigerator, set at three, was happy. It was keeping the refrigerator cold. However, the freezer was a different story, even though it was approaching 26 degrees outside (unknown what the interior trailer temps were) it does not have a thermistor different from the refrigerator so it started warming up and melted my ice cream.

Later in the morning I did manage to get the freezer to kick in by opening the refrigerator door. In less than 30 minutes the freezer dropped 2 degrees. Probably not a long term solution. This may not be an issue unique to this model of refrigerator, as any two compartment refrigerator with a single thermistor will have this problem. Not sure if this would occur if the trailer was occupied and the furnace running. Stay tuned for that tomorrow.

So has anyone else encountered this problem and are there any solutions to it? I know one, don't carry ice cream bars.

[steve dunham]

It may be the same problem people have with refrigerators that are placed in unseated areas The refrigerator stays cool enough that the thermostat does not call for cooling and the refrigerator does not run often enough to keep the freezer cold .
We have a refrigerator in our guest cabin and in order to keep things in the freezer frozen we have to keep the cabin at 50 deg or higher

[Brian B-P]

Steve nailed it - this will happen with any refrigerator which is operated in an unheated area. Although I have a Dometic RMD-series refrigerator, I have had this happen with a Norcold in another RV; it is not a fault of the refrigerator's design, and not a failure of the refrigerator to operate properly.

Because RV absorption refrigerators are exposed to the outside, this can even happen with a reasonable RV interior temperature combined with low enough outside temperature, because the refrigerator section might lose enough heat out the back to stay cool enough without running much, while that's inadequate running time to keep the freezer cold enough. I had that with the Norcold.

[rubicon327]

Oh boy...I have fought to get ours to work well in hot weather but there are is an interesting dilemma when it is too cold outside as well. This is how I saw it best described on another forum...

"...If the fridge gets cool but the freezer doesn't freeze, the problem is that in cool weather, the system is too efficient. The fridge cools quickly, and because the thermostat (thermistor actually) is in the fridge section, the cooling unit just does not run long enough to properly cool the freezer."

"...the freezer begins to climb towards the same temp as the fridge, where the thermistor is located. This is especially true if the inside of the RV is cold and the door isn't being opened."

The same thing happens to my residential fridge in the garage in winter.

There are several hacks that guys have come up with online including overriding interior fridge lights (incandescent I presume) to stay on or putting a regular incandescent bulb in the exterior compartment of the fridge being careful not to touch anything that could melt. While I know these absorption fridges pretty well I don't have any experience with these hacks described above. Maybe a member who regularly camps in freezing weather will chime in.

[Brian B-P]

Originally Posted by rubicon327

This is how I saw it best described on another forum...

"...If the fridge gets cool but the freezer doesn't freeze, the problem is that in cool weather, the system is too efficient. The fridge cools quickly, and because the thermostat (thermistor actually) is in the fridge section, the cooling unit just does not run long enough to properly cool the freezer."

This description is of the behaviour is fine, but the assumed cause is not correct. The system is not "too efficient"; the demands of the cooler (refrigerator) and freezer sections are just not in the same balance as they would be in different ambient conditions.

A full solution would not be an inefficient refrigerator , it would be one with separate (and separately controlled) cooling units for the two sections. Good home refrigerators (which are all compressor-based systems) actually do this, but it would be expensive (and impractical in a small size) to do this in an RV absorption refrigerator.

[cpaharley2008]

I thought I saw a winter cover available for the Dometic european models that covered the lower outside vent for winter use on 120v only, would that help, I wonder?

[elongest]

I had something similar happen last month on a 2 week trip with a RMD 8555. After a week of good operation in hot humid conditions the freezer temp started to rise and the frig. box temperature stayed steady. The cooling fins inside my refrigerator had iced up. The ice on the cooling fins was keeping the refrigerator box cold so there was no need for the boiler to operate to keep the freezer cold. A quick defrost using my cube heater returned the refrigerator operation to normal. FYI: My thermometer is free hanging, the frig was pretty full ( cold thermal mass) and my frig is lined with 1" foam so it holds the cold pretty well.
I think someone else reported the freezer warming up in extreme cold conditions about two months ago. With one cooling coil for the freezer and frig. and one thermostat there is not much you can do. Running the furnace should help matters.
Eddie

[Brian B-P]

Originally Posted by cpaharley2008

I thought I saw a winter cover available for the Dometic european models that covered the lower outside vent for winter use on 120v only, would that help, I wonder?

Not likely. The purpose of the winter cover is to keep some parts of the cooling unit from getting too cold and freezing up. If the cooling unit freezes up the whole thing stops working, which was not the problem in this case.

I have had a Dometic RMD freeze up; it just didn't work until spring, then resumed as if nothing were wrong.

[rubicon327]

Originally Posted by Brian B-P

This description is of the behaviour is fine, but the assumed cause is not correct. The system is not "too efficient"; the demands of the cooler (refrigerator) and freezer sections are just not in the same balance as they would be in different ambient conditions.

Agreed Brian. Too efficient is a poor choice of words. That’s what I get for quoting what someone else said!

[tractors1]

Very interesting thread; had not thought of the cooling system as actually two systems with a single point of control (thermistor.) I was planning to pull the fridge out this winter and insulate the entire enclosure.



I have experimented with different thicknesses of packing Styrofoam inside both compartments and found that less foam thickness in the fridge compared to the freezer kept the freezer colder so wifey's frozen fudge bars weren't as soft. I also have the freezer door insulated.



Think I'll try some EPS (Expanded Polystyrene ) first as it's a lot less fragile and can be machined to fit better in the fridge section.

[Brian B-P]

Originally Posted by tractors1

I have experimented with different thicknesses of packing Styrofoam inside both compartments...

Think I'll try some EPS (Expanded Polystyrene ) first as it's a lot less fragile and can be machined to fit better in the fridge section.

You might consider polyisocyanurate foam, which has a higher R-value and also machinable.

[Brian B-P]

Originally Posted by tractors1

Very interesting thread; had not thought of the cooling system as actually two systems with a single point of control (thermistor.)

Well, really one system with two evaporators... #5 and #6 in this diagram:

[Ron in BC]

Originally Posted by fudge_brownie

Why did my ice cream bars melt with the refrigerator compartment remaining at a very constant 36 degrees?

Oh man, I wouldn't mind if my lettuce wilted but if my ice cream bars melted

Interesting situation and maybe answers a few questions others might have had when in a similar situation.

Ron

[tractors1]

Originally Posted by Brian B-P

You might consider polyisocyanurate foam, which has a higher R-value and also machinable.

True, but the cost difference per R isn't worth it when you can't buy it in small quantities.

[fudge_brownie]

Nice observations. Not having a cabin in the “northwoods” or a refrigerator in the garage I never encountered the problem.

As expected, once we parked for the evening and turned on the furnace, the freezer started cooling. At my 8:00 PM feeding my ice cream bar was solid. SensorPush shows we were hovering around 3 degrees F.

[Brian B-P]

Originally Posted by tractors1

True, but the cost difference per R isn't worth it when you can't buy it in small quantities.

Since it's normally a building insulation material, the minimum does appear to be a $30 4'x8' sheet.

[Greg A]

Originally Posted by fudge_brownie

Nice observations. Not having a cabin in the “northwoods” or a refrigerator in the garage I never encountered the problem.

As expected, once we parked for the evening and turned on the furnace, the freezer started cooling. At my 8:00 PM feeding my ice cream bar was solid. SensorPush shows we were hovering around 3 degrees F.

Would it resolve if you run the furnace at say 55 when prepping for the trip and then tow with the furnace on as Reace had us do on our way home from pickup?

[fudge_brownie]

Originally Posted by Greg A

Would it resolve if you run the furnace at say 55 when prepping for the trip and then tow with the furnace on as Reace had us do on our way home from pickup?

I would say yes, but I have never received consistent feedback on the furnace running while towing. Seems the forum opinions were all over the place. Being a late February Snowbird I have it in my plan, if necessary.

I think if you are placing frozen items in a freezer, like meat and vegetables - no problem. Ice cream, especially any of those skinny versions, read low fat, and you encounter a quicker melting point.

[Brian B-P]

Originally Posted by Greg A

Would it resolve if you run the furnace at say 55 when prepping for the trip and then tow with the furnace on as Reace had us do on our way home from pickup?

This would likely work, unless it is very cold outside.

Originally Posted by fudge_brownie

I would say yes, but I have never received consistent feedback on the furnace running while towing. Seems the forum opinions were all over the place...

Some people have had problems with refrigerators operating on propane while moving, due to air flow issues. I wouldn't be surprised if water heaters could have similar problems, although that has always worked for me. Unlike both refrigerators and (conventional) water heaters, the furnace has a fan-forced draft (combustion air is blown through the furnace), so it should have no issues with the highway-speed wind blowing past it.

Of course to have the furnace running the propane tank valve must be open. Hopefully we can skip a repeat of that debate

[mizterwizard]

Older equipment had trouble with air flow on the road but newer RVs can generally tolerate wind at any speed from all sides. At least mine can.

It shouldn't be a problem to keep your appliances running on propane all of the time.