Dometic RM2652 not cooling

[Travelin2]

We bought a 2002 Bigfoot trailer recently and I knew the fridge may be questionable because the rig sat for a long time without any operation of the appliances. The fridge cools a bit when running on 120AC but when on gas it does nothing. The gas burner lights and runs very nicely with a clean blue flame. It relights immediately when I blow it out and the flue is hot with lots of heat escaping out the top of the tube with the baffle in it. I unplugged the thermistor at the circuit board and ran it on gas for about 3 hours. At the end of that time the coils and the big canister at the bottom of the coils was just ambient temperature. I have wireless temp sensors inside the freezer and fridge and no temperature change whatsoever...still ambient temp. I'm not sure why it cooled some while on the electric heater???

I am thinking the cooling unit is Tits Up. I would be interested to hear what you may think. I appreciate any and all views and opinions...thanks.

John

[jkwilson]

Gaining an understanding of all this stuff is invaluable. I hate to spend money when I don’t need to, but it seems like you needed to and made sure of it.

[Travelin2]

John,

I would have replaced just the cooling unit but the inside of the refrigerator was all yellowed. We thought it was due to the previous owner using some type of cleaner that discolored it but one of the professional guys that work on these and help us out here on the forum,Chris Bryant, responded that the yellowed plastic liner is a sign that the ammonia has leaked into that compartment. If only I would have mentioned that earlier, it would have saved me lots of work. Because of the yellowing we decided to buy a complete unit. One really good part of this rigamarole that I went through, I discovered that the gas pressure was only 9.8 inches of water column. I turned it up to 11 inches and now the cook stove lights off much better. The extra pressure is evidently making the gas get to the sparker quicker.


Here is a link to the discussion that led to Chris figuring out the clue to reason for all my headaches...
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29836674/srt/pa/pging/1/page/1.cfm

[jkwilson]

Sorry you had to take the kick in the wallet. I’d guess with all you’ve done you’d have shaken out the problem if it was repairable. Only guess left is a cracked weld for the flue pipe which means a new cooling unit anyway.

[Travelin2]

Well fellas, I want to thank you all for staying with me and wading through this dilemma with me. When JKWilson said to check the orifice to make sure it was the proper size, I went right out and checked it and it was the proper one he mentioned and that was it, I called it a game and went to town and bought a new one. It's still sitting in my truck and I will unload it in the morning. I think I am close to a solution for melted ice cream and am looking forward to some cold brewskies at camp.

[Gjac]

John you have done a very thorough job investigating, cleaning and documenting the problem. You know your cooling unit is fine because it cools on AC. Your flue is clean with a new baffle and you adjusted the propane pressure. The only thing left is the orifice and the burner tube. John Wilson already spoke about the orifice. The last thing to check is the slots in the burner tube. Is it the original one? I know on mine after about 17 years and multiple cleanings with a wire brush the slots became wide allowing more air to the propane mixture. Does the flame flicker at all? Try covering one of the slots with a screw driver tip does the flame get any brighter?

[Travelin2]

Will do JK. I did remove it and blew it out. looking through it looks good. I could see the ruby in there. I did not pay attention to the number.

[jkwilson]

I'd try a new orifice before giving up. If somebody stuck something in it, they probably damaged it. Or somebody replaced it with the wrong one for your unit. This isn't just a chunk of brass with a hole in it. There's a man made ruby that's laser drilled inside.

At least verify you have the correct #58 orifice in there.

[Travelin2]

As a last resort I did the burping thing even though Doug pooh-pooed it(I have come to value Dougs opinion) since, There was nothing left to do and I really didn't want to put a thousand bucks into a seventeen year old trailer. I also bought a new baffle on a whim and it did fit the flue tighter than the old one but after burping and installing the baffle and running it on gas for about 14 hours, the fridge section was only about 10 degrees colder than ambient. So I'm outta ideas, so here's where I'm at now....
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/29836674.cfm

[Gjac]

How are you making out with your problem?

[dougrainer]

Travelin2 wrote:
I want to run something by you guys that a fellow was telling me about my fridge not cooling. We were at an RV rally and I got to chatting with a fellow RVer. When I described the strangeness of this fridge cooling good on AC and very poorly on propane and all I had done to make sure the propane side was functioning properly, he had a theory and a fix. He thinks that the fact that this rig sat unused for an extended period that the solution inside the cooling unit separated out by settlement and blocked or partially blocked the tubes feeding the boiler. Enough solution is passing the blockage for the electric element to heat and cause a circulation to occur but when the extra heat of the gas is applied, it boils the boiler chamber dry because the solution cannot feed the chamber fast enough and it basically becomes vapor locked. He claimed that the blockage in the system can be cleared by removing the fridge and up-ending it and letting it stand upside down for several hours, at which time I would reinstall it and start it on gas. I was hoping someone here has heard of this before as an accepted thing to do or am I being led on a "snipe hunt"?

OLD wives tale. Not true. When you burp you do indeed "rearrange" the ammonia mixture, but if TRULY blocked this just bypasses for a few weeks and will go back to not cooling. Doug

[Travelin2]

I want to run something by you guys that a fellow was telling me about my fridge not cooling. We were at an RV rally and I got to chatting with a fellow RVer. When I described the strangeness of this fridge cooling good on AC and very poorly on propane and all I had done to make sure the propane side was functioning properly, he had a theory and a fix. He thinks that the fact that this rig sat unused for an extended period that the solution inside the cooling unit separated out by settlement and blocked or partially blocked the tubes feeding the boiler. Enough solution is passing the blockage for the electric element to heat and cause a circulation to occur but when the extra heat of the gas is applied, it boils the boiler chamber dry because the solution cannot feed the chamber fast enough and it basically becomes vapor locked. He claimed that the blockage in the system can be cleared by removing the fridge and up-ending it and letting it stand upside down for several hours, at which time I would reinstall it and start it on gas. I was hoping someone here has heard of this before as an accepted thing to do or am I being led on a "snipe hunt"?

[jkwilson]

Travelin2 wrote:
I guess I can check to see if a new baffle is available. Maybe the tolerance is too great on the sides of the old baffle and the heat does not linger long enough. I know when it is running, I can reach my fingers up to the top of the flue tube and there is a lot of heat coming out. It will burn you in a hurry.

Only thing that really seems plausible to me. Maybe if you can measure the diameter of yours vs. the diameter of the flue and then compare to the diameter of a new one. Also, check the position in the flue.

[Travelin2]

The baffle was in there and very rusty. I cleaned all the rust off with a drum sander on my Dremel. I did find a specification after I had already reinstalled it that specified a 1 7/8 inch recess to the bottom of the baffle from the bottom of the flue. I did not measure this because it was already running. I have turned it off now so it is cool enough to measure. It seems odd that that measurement would be critical but I will check it.


I know that the flue for the propane burner is welded to the same boiler as the pocket for the electric electrode but for some reason the heat from the gas flame is not heating up the flue as intended. The insulation and the metal holding it has not been disturbed and looks as new. I wonder if it is possible to get a bad weld by a beginner that is mostly slag or do you think they are welded by robotics that don't make mistakes. I guess I can check to see if a new baffle is available. Maybe the tolerance is too great on the sides of the old baffle and the heat does not linger long enough. I know when it is running, I can reach my fingers up to the top of the flue tube and there is a lot of heat coming out. It will burn you in a hurry.

[jkwilson]

The gas flame and elecric element both heat the same chunk of metal.

Your electric readings show your cooling unit is working.

All comes down to the fact that you aren't getting enough heat to transfer from the burner flame to the boiler.

My next guess would be a missing or rusted out flue baffle. Does yours have the spiral thing that goes in the flue to help retain heat in the boiler? If this is missing, I can see how it would cause your problem.