Fixing underperforming Dometic RM2354

[JohnnyFry]

Follow up on Dometic 3 way fridge.
Some weeks ago I asked the group if anyone has experience with “Burping” a Domestic Ammonia cycle fridge and got mixed reviews. After researching further on the web I began to realize that the real problem was inadequate ventilation on the fridge backside. The fridge had a”Snyder kit” fan and plastic duct made from downspout gutter parts. As it turned out that fan had failed unbeknownst to me. Performance was terrible and had seriously deteriorated, probably due to the fan failure

I decided to go all in and overhaul the entire ventilation scheme as well as go through the power wiring for the unit.
First off I found a poor 12V power ground and other questionable connections— I corrected those.
Second, I installed additional insulation on the top of the unit and installed a air deflector to route the air toward the upper louvers. I sealed everything with metal duct tape.
Third, I installed 3 90mm fans on the upper grille and sealed all openings on the grille except for the fan exhaust. I also re-installed the Snyder duct with a new high flow 80mm fan.
Forth, I installed dual 60mm fans directly on the fins inside the fridge.

The fans on the interior of the fridge run 100% of the time, the outside fans are controlled by an ARP Fridge Defend controller and come on when the condenser fins reach 100°F and turn off at 90°F.

Initial testing gave good results on 120 VAC and excellent results on Propane. After 12 hours on AC the Freezer was at -6°F and the Box was running 40°F, Switching to Propane dropped the Freezer to -9°F and the box to 31°F. This was on setting 5. This was at 84°F ambient dropping to 71°F during the night.
Loading up the fridge and taking off on a weekend trip the fridge setting was put on 3. Through the trip the freezer maintained a consistent -6°F and the box ran 35°-38° through the trip,

Overall I am very satisfied with the performance of the unit after having struggled with warm beer and spoiled milk for fat too long!

[booster]

Have you measured the total amps drawn by the 5 fans and the controller? That is always interesting to see.

[JohnnyFry]

Yes, I have: The fans inside the fridge draw 150mA, the outside fans draw 480mA The ARP controller burden is 40 mA. So the total is 670mA plus the gas solenoid valve when the fridge is running.

[Philip53]

All of those fans will make a big difference in cooling performance. I have found that only propane gives good results in most any condition, with 120v second. Never ran any of my 3 ways on 12 volts, I thought that was a bad idea all around. Many problems reported with burned/melted control boards and general poor cooling.

I installed an Isotherm Cruise 195 with dual compressors in my new van conversion, and after a bit of fan 'tweaking', I have great cooling without having to worry about being level.

[GallenH]

Personally I think that being level is overrated. I rarely find a campsite that is perfectly level. Even Dometic says that it should be reasonably level with no noticeable sloping of camper walls…not perfectly level. I guess my point would be that I wouldn’t want to sleep in a camper so skewed that the fridge has exceeded Dometic,s specs. Just my opinion.

[Philip53]

Originally Posted by GallenH

Personally I think that being level is overrated. I rarely find a campsite that is perfectly level. Even Dometic says that it should be reasonably level with no noticeable sloping of camper walls…not perfectly level. I guess my point would be that I wouldn’t want to sleep in a camper so skewed that the fridge has exceeded Dometic,s specs. Just my opinion.

Hey Gallen, I thought exactly what you stated, and indeed that was the case for years, until I took my '17 Navion to Yellowstone. I backed in at the campsite and had the rear just a little higher than I normally do, plus, that puts our heads in a little better position when sleeping, so the RV slope was OK with us.

I noticed right away that the fridge was not cooling as it had been, but did not think too much of it, but it continued to have poor cooling for our entire 5 day stay. I was beginning to believe I had some issue with it. On the way back home, and during each of our overnight stays, the fridge was back to performing just fine. The only thing I can attribute that poor fridge performance during our stay, was the greater than usual slope rear to front.

We must have been right at the edge of that levelness thing, so I now believe there is something to keeping those absorbtion fridges as close to level as you can.

Oh, the temps at Yellowstone, they were very cool. In fact it snowed for one of those days.

[JohnnyFry]

This has been addressed many times in this and in other forums: According to a Dometic factory rep (personal communication at an FMCA Rally), the spec is: ±3° side to side of the fridge (front to back of the vehicle in most class B vans) and ±6° front to back of the fridge. This is for ANY mode of operation (gas or electric). When you exceed these valued the boiler will begin to overheat within 15 minutes and result in decreased performance. More importantly it will begin irreversible damage to the cooling unit, which, if continued over time, will result in total destruction of the cooling unit. The damage is progressive and by the time you begin to notice loss of performance it is too late. The reason it happens is that the steel tubing of the cooling unit is protected from corrosion damage by the addition of K2CrO4 (Potassium Chromate) to the water in the system. When the overheating occurs two things occur:The Potassium Chromate precipitates out of solution in crystals which begin to block the smaller passages in the cooling system and second, loss of the Potassium Chromate in solution causes loss of corrosion protection and allows the ammonia in the system to attack the tube walls causing eventual failure...the resulting leaking of ammonia and hydrogen is a major fause of fridge fires. Bottom line: use a level and keep it level!