Dometic RM2852 stopped cooling despite flame and element working

[Mark77]

My refrigerator (Dometic RM2852) abruptly quit cooling. Went from working perfect to not at all.

No tell-tale signs of ammonia leak. Lights on the front work as normal, no check light.

I do have the manual with troubleshooting steps, but no time to deal with that right now.

I am curious if anyone else has had this happen and what the issue was.

 

[Mark77]

I found a service manual online and VOM in hand, went through all of the testing. Everything is as it should be... Flame stays lit, Electric element draws 2.7 amps (in spec) and when I fired it up the absorption chamber heated up as it should for about the first 15 minutes of operation. Then nothing. Boiler flame doing its thing, but absolutely no cooling.

My absorption fridge is toast, pardon the pun.

Now decision time. Do I replace with a new cooling unit? Convert to compressor type? Residential option? I also need to think about resale value if that need arises. One thing for sure, it would not sell without a refrigerator.

Anyone have any advice?

 

[Carl n Susan]

I admit, I don't really understand the cooling process all that well. But ammonia/water/hydrogen heating/separation/freeze process is contained within the cooling tube system. Assuming there isn't a leak, that closed system is not subject to failure. If it gets heated (by electric element or propane flame) it boils the ammonia which iteracts with the hydrogen to cause freezing.

The control board and sensors turn the Heat (element/propane) on and off depending on temps. It seems that area is the most likely failure area.

Is it turning off the electric element after 15 minutes? That is way too soon as it takes hours to cool down from ambient temps.

 

[Mark77]

Per the service manual Carl, I unplugged the thermistor from the control board which forces either the gas, or electric heating element on continuously. It happed to be running on gas at the time and the flame never went out, and nothing on the back end got even warm.

While the thermistor was unplugged I checked the resistance per the manual and it showed 8500 ohms when the thermistor was sitting in ice water in the refrigerator. Spec said 8000 to 10,000 ohms so that checked out.

After 2 hours running, with the thermistor unplugged the freezer floor temp as 81˚. Not even trying to cool.

Flow chart in the manual says if no leak is evident, the cooling unit is likely plugged and is not serviceable so it needs to be replaced.

Not happy, but looks like I need to either repair it or replace it.

 

[Carl n Susan]

I overlooked a plugged cooling unit as that isn't a common problem. I recall others have had good success with a replacement cooling system. Relatively inexpensive compared to buying a replacement. But I think I would go with an even cheaper residential refer as you have the solar/batteries to support it.

 

[scottandsusan]

Many years ago, about three campers ago, we replaced the cooling unit with one of the Amish built units. It wasn't to bad of a job. If I had to do it today, I'd convert it to one of the 12 volt units.

 

[Mark77]

A friend of mine told me last night that in his cabin they have a 17 cu ft LP only refrigerator (absorbtion). It came with a long brush to clean the chimney, and he does so at least once a season.

He suggested I check the possibility that there could be an obstruction in the chimney. Never thought of that, but I do know that the bottom section of the boiler on mine gets crazy hot. Maybe he is on to something. While not probable, it is possible that some insect built a nest in the chimney and is not letting heat rise up though the chimney like it should. It will cost me 15 minutes to fins out.

If not, I have found a replacement 120 VAC refrigerator that will fit in that cabinet nearly perfectly for under $400. It has more room inside (10.1 cu ft) and will cool faster, colder, and more reliable. It draws 130 watts running and 175 watts in the defrost cycle. That is easily doable with a small inverter when on a long travel day if you need to and at 130 watts is far less of a load than your toaster or coffee maker. My current Victron / lithium system would not even know it's there, especially coupled with the DC / DC charger on travel days.

I'll post back what I find with the chimney.

 

[Harrishome2005]

I have a 2017 Montana 3000re. I just replaced my absorption cooling system with a JC Refrigeration 12 volt cooling system and so far we love it. We were constantly having trouble keeping the refrigerator at 40 degrees or below, not any more.

 

[Mark77]

No luck on the chimney thing... I was fascinated by what I found in there! I took a picture of it (below) and it reminded me of punching flues on the old steam traction engines I used to run a few years back.

No way would there be soot in there as it is an LP flame, but the device could pull out a nest if one ever got in there. Noted when I was up there the condenser was very hot, 130˚ but after 3 hours there was no evidence of cooling. I think the cooling unit is shot.

Anyway, pictures of that flue tube "cleaner" below.

 

[Oregon Coast]

Even though I have worked on thousands of commercial refrigeration units, I am RV ammonia dumb. However, one problem you might have is if the refrigerant has separated. Years ago, a service guy explained how the refrigerant can isolate and accumulate in the wrong location of the system. He said to remove the refrigerator, turn it upside down, which will sometimes force the refrigerant to relocate. But I have no experience with this. After typing the above, I searched for "turn rv refrigerator upside down" on google, and found good info. It is called burping. Good Luck.

 

[Mark77]

Even though I have worked on thousands of commercial refrigeration units, I am RV ammonia dumb. However, one problem you might have is if the refrigerant has separated. Years ago, a service guy explained how the refrigerant can isolate and accumulate in the wrong location of the system. He said to remove the refrigerator, turn it upside down, which will sometimes force the refrigerant to relocate. But I have no experience with this. After typing the above, I searched for "turn rv refrigerator upside down" on google, and found good info. It is called burping. Good Luck.

Might try that. I have to pull it out regardless and could easily test it on electric before I buy anything new.