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Old 12-06-2019, 04:26 PM   #1
LHaven
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Fridge won't cool

I have a guest with a Dometic RM1350MIMSSX that isn't cooling. It was working fine until about a week ago. Since the traveling repairman can't come until next week, they asked me to give it a lookover.

He says it doesn't cool on either propane or shore power. I can hear the propane igniting and running when it should, and I know it sees shore power because it turns the propane on and off when I flip the fridge breaker in the main box. There are two mid-height fans that cycle on and off periodically at what seem like appropriate intervals. The unit is in a slide.

I checked every fuse in the main box for a blowout (because not a single slot was identified!) I pulled the spade mini-fuse in the control board box and inspected the tube fuse visually, and they both appeared good. I inspected all pin/socket connections for tightness.

I found an AC cord that had never been plugged into an outlet and plugged it in, but it didn't help. I'm pretty sure from the schematic that it must be the one that runs the icemaker, which they have never used (they're not even sure it's plumbed).

The refrigerant tubing in all accessible locations feels to be at ambient, neither cold nor hot.

My best guess at this point is that he has either lost his refrigerant, or has a bad control board. Since I'm not sure what causes the refrigerant to circulate in a pumpless system, I'm not sure if a control board failure would cause this symptom... especially since the tubes still show no temperature differential when propane is running.

Any ideas as to what is likely to be the problem?

One thing I will add is that the owner added (very professionally, I think) a third rectangular access port in the skin halfway up the rear of the fridge, around where the fans are located. But it's a vented access port like the other two. That makes me wonder if maybe he fell afoul of the issue where people find the piece of plywood "blocking" the fan's airflow in the slide and remove it, only to find out that it was there on purpose.
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Old 12-06-2019, 04:56 PM   #2
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System is very simple. If flame or 110 volt heating element come on and pipes get hot, it will make cold. If pipes get hot and refrigerator doesn't get cold, cooling unit is blocked or coolant leaked out...need new unit or refrigerator.

I don't think 3rd access point was a good idea, makes it harder to create "chimney" effect which is already a problem when refrigerator is mounted in slide. I would block off that vent and make sure that wood, baffle, etc is properly placed in top opening.
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Old 12-06-2019, 05:44 PM   #3
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As stated, if the chimney is hot and the cooks aren’t hot then the cooling unit has failed. DO NOT remove that baffle, it’s there for a reason.

CAREFULLY remove the lower access panel and look for any signs of a yellow powde. If you see any STAY AWAY from it, as it’s NOT GOOD.
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Old 12-06-2019, 05:54 PM   #4
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I never did open the top baffle as it was way over my head and all the interesting parts seemed to be at the bottom anyway. I just sent the owner an email to ask him to check whether there was a baffle on his top vent, and if so, to see what he could do about blocking the airflow from the central vent.

I'm not sure why he installed the central vent, but it may have had something to do with the fact that he replaced the original refrigerator at one point with an upgrade, and maybe he needed access to that area when he did it.

I didn't see any yellow powder, at least nothing I could distinguish from normal Arizona dust. There was a bunch of tarry black melted patches on the wiring, but I assumed it was just vent waterproofing caulk that transferred onto the wires in hot weather.
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Old 12-06-2019, 07:18 PM   #5
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The yellow powder is a mixture of Sulphur and chromate. Both are "on the California list" and should be avoided (because they're on every other state's list too)…

That said, if you see the powder, it means there is a hole in the refrigerant system and "everything that makes it work is gone"... You might ask them if they have recently smelled ammonia. If so, that's the "other stuff that's in the refrigerant system" and is a "dead ringer" for a "dead reefer"....

As for "how the refrigerant is pumped": It's the same theory of action as a percolator coffee pot. The heat boils the refrigerant, it expands and turns into a gas, the gas "perks" up the chimney under pressure, as it enters the evaporator, (expanding gas cools and absorbs heat) as it flows (or is pushed) out of the evaporator into the condensing coils (releasing that heat to be blown up the vent stack by the fans) as the gas returns to liquid form and enters the chimney to be turned to a gas by the heat and repeat the "perking cycle".
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Old 12-06-2019, 07:41 PM   #6
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Quote:
Originally Posted by JRTJH View Post
As for "how the refrigerant is pumped": It's the same theory of action as a percolator coffee pot. The heat boils the refrigerant, it expands and turns into a gas, the gas "perks" up the chimney under pressure, as it enters the evaporator, (expanding gas cools and absorbs heat) as it flows (or is pushed) out of the evaporator into the condensing coils (releasing that heat to be blown up the vent stack by the fans) as the gas returns to liquid form and enters the chimney to be turned to a gas by the heat and repeat the "perking cycle".
Yeah, I think I remember this cycle from a fridge I had in a 1970 Skamper pop-up. Then my question is, why is the control board necessary at all? It sounds like nothing in this cycle requires electricity. (Well, maybe the propane ignition, though I once had a tankless house water heater that just had a turbine run a sparker and needed no electricity at all.) Or is it just a question of temperature control?
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Old 12-06-2019, 08:05 PM   #7
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The control board is needed to “decide” if the heat source will be the electric element or the LP flame. It also gets a signal from the thermistor inside the fridge to determine temp and the need to start the heating cycle. The “eye brow” ( buttons on the front) are used to tell the control board “what you want”.

Simple explanation. There’s more to it but that’s the Friday night, I’m too tired version.
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Old 12-06-2019, 09:18 PM   #8
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If any are really wanting to know how these absorption fridges work, go to this link https://www.arprv.com/ and way down on the left side are links to Escapee Magazine articles that will give a pretty good education on how these units work.
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Old 12-06-2019, 11:07 PM   #9
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Did you try the high temp reset button above the burner tube? Mine is behind a piece of sheet metal which comes off with a couple of screws. The last time my fridge stopped working that was the problem.
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Old 12-06-2019, 11:09 PM   #10
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Quote:
Originally Posted by Logan X View Post
Did you try the high temp reset button above the burner tube?
Wow, that thing's a button?

I didn't fool around in the vicinity of the burner tube, as it was pretty hot. I'll tell the owner to look for it and give it a jab.
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Old 12-06-2019, 11:13 PM   #11
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Quote:
Originally Posted by LHaven View Post
Wow, that thing's a button?

I didn't fool around in the vicinity of the burner tube, as it was pretty hot. I'll tell the owner to look for it and give it a jab.

If the burner tube was hot then that may not be the problem. But maybe it’s worth a look. Mine is behind a piece of sheet metal that has to be removed with a couple of screws. The reset button is right in between the two electrical connections.
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Old 12-06-2019, 11:16 PM   #12
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The propane works just fine. I can't tell whether the electric heater works fine, but I suspect it does, as even the propane doesn't get the fridge cool or the fluid tubes hot, and the probability of two things going wrong at once is low.
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Old 12-07-2019, 01:13 AM   #13
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Quote:
Originally Posted by Logan X View Post
Did you try the high temp reset button above the burner tube? Mine is behind a piece of sheet metal which comes off with a couple of screws. The last time my fridge stopped working that was the problem.


If that is tripped, the fridge won’t even start up.
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