Clean those jets.

[The Minimalist]

There is a lot of discussion on this site regarding the efficiency of absorption refrigerators. Our friend Bob Miller mentioned in another thread that a Dometic engineer told him that the refrigerators should work best on LP, followed by AC and then DC.

My Dometic RM-2193 has never worked on LP as well as on AC in hot weather, 80 degree F and above, despite my having cleaned the burner and the flue on a couple of occasions. I never cleaned the jet because it looked nice and shiny, and frankly it looked so fragile that I was afraid to pop it out. In addition, I have added ducting and a computer fan to improve air flow over the condenser fins and added insulation to the outside of the unit.

Looking on YouTube I found this short video on cleaning the burner:

www.youtube.com/watch?v=gSrVU7MRBUo

Turns out a sharp tap of the burner tube on a hard surface removes the jet neatly. He used Goof Off to clean the jet and the burner, blowing out with air pressure.

Anyway, I did the cleaning routine again; jet, burner and tube, flue and the flue baffle.

Per the video example I used Goof Off to clean the jet and burner and blew them out with compressed air.

I began operating the refer last night on LP and despite an 80 degree night it got down to 35 F. Today has been cooler than usual, only 95 F outside, but the reefer never got above 42 F. So, it's maintaining at 53 degrees F below ambient.
I found the improvement impressive so, inquiring minds have got to know, I did a little research and here’s what I found:
The #45 jet (.082 in) on my reefer, at 11 lb water column pressure, should put out 46969 BTUs of heat. If a small particle of dirt or deposits reduce the size of the jet to a #46 (.081 in or 1/1000th less diameter) you will get only 45831, or 1138 fewer BTUs. A deposit reducing the orifice to the equivalent of #47 orifice (.0785 in) you will get 43045 BTUs, or 3924 fewer BTUs than design output. Long story short; it doesn’t take much debris or deposits to rob your unit of its LP efficiency.
So, despite it being clean and shiny looking and seeing no debris in it when held up to a magnifier under light, my jet needed to be cleaned.
Goof Off and canned air will be part of my road kit from now on, and burner and jet cleaning are now part of my annual prep.
You can find the orifice data here:

http://www.davegardner.org/images/Ga...ificeTable.pdf

[Bob Miller]

Good stuff Clif. thanks for listing your experience. I use alcohol for cleaning jets and, if it doesn't help I drink some and don't worry... LOL


It is very important that a dirty jet may not "Look" dirty and, if cleaning it fails, just replace it, as the p.o. may have tried cleaning it with a wire and distorted the opening, which is a lot more than just a hole. Dometic still has them in stock. A new one brought mine right back to "As New" for cooling.

[barriebarry]

I know this is an old thread but just wondering if anyone can confirm what the #45 means for the hole size. It cannot be 0.082" as stated in the original post as a quick comparison with the calipers suggest that the hole is closer to 0.020" - hard to tell with something that small. The wire gauge size 45 = 0.0018" so does that make sense?

[Nick G]

I can’t say what size the holes are in the jets but a #45 drill bit is 0.082” dia. Perhaps the jets are sized to numbered drill bit sizings. It’s probably tough to measure a hole that small with a calliper.