3 year old Dometic doesn't work

[ROBERT CROSS]

BC,

I've always been led to believe that the cooling units were installed several degrees off plumb to enable proper circulation. So our leveling of the trailer would ensure the system will work as designed....am I rong?

Bob

[damonbeals]

Okay I give, what was the fix!

[Buttercup]

Originally Posted by Aage

Answer: a plugged vent in the area behind the refer?

Just gotta say this has been an exceptionally interesting thread for me, since I am moving toward installing a used refer in my TT where there has been a compressor-type since we bought Henri (my TT). The unit is sitting in my shed just waiting to have its operation confirmed before I install it.

I love the thermocouples you added; great way to really know what is happening with the refer!

I can't recall if you installed vent fans to cool inside the refer and in the enclosure it's in. if you did, would you please share what size and CFM type you put in?

Thanks!
Aage

Aage, thank you for playing. Your answer is incorrect. Please try again later.

Henri is such a cute name for a trailer. Great choice. My suggestion to you would be to pull out that fridge, set it in level ground and plug that heating element in to see if the unit works. You may have to make a cord to power the heater directly but that is the best way to test it. You don't need anything special, just a power cord hooked up to the heater directly. Check the resistance of the element first to be within 10% of the listed specs for your unit.

Once plugged in, you should start to see cooling in the freezer in about an hour. You can keep it plugged in for hours to see what temp it gets down to. It does not need to be in a cabinet to test like this. If you have one of those Radio Shack optical thermal sensors you can measure around the back of the fridge to see that it is working.

I did install a vent fan and baffle on the top of the fridge that will draw air through the condenser fins as needed to remove excess heat. This has been a problem for us in that with the fridge running, it would hear up out cabinets on the left hand side. This fan will totally solve that problem. It is a 7" car radiator fan that I hooked up to a speed regulator to control the air flow and noise to an acceptable level. I dial it down to about 6 watts of draw and it is very quiet but does a great job of keeping the cabinet cool. We will see how it handles Midwest heat.

[Buttercup]

Originally Posted by ROBERT CROSS

BC,

I've always been led to believe that the cooling units were installed several degrees off plumb to enable proper circulation. So our leveling of the trailer would ensure the system will work as designed....am I rong?

Bob

Bob, I am not an expert but my answer would be yes, you are wrong. At a reasonable level, the liquid fluids drain in the direction they are supposed to. Operating off level could actually impede or stop proper fluid movement in the unit.
The coils all have a little bit if slope in them to ensure the liquid fluids move where they should.

[Buttercup]

Originally Posted by damonbeals

Okay I give, what was the fix!

Damon! Come on!!!! Think about it. Put on yer thinking cap. I want to give others a chance to really ponder this.

[Foiled Again]

The roof exhaust vent was full of pine needles and leaves.

Paula

[Buttercup]

Originally Posted by Foiled Again

The roof exhaust vent was full of pine needles and leaves.

Paula

Nope, it has more than adequate ventilation. Isn't this a fun game!!!!

[Buttercup]

I guess I will have to let the cat out of the bag on this a little. The problem was one of TOO MUCH COOLING. It wasn't snuffing out the flame because the boiler was still hot. It is still boiling ammonia. But with too much air flow, it was cooling not only the boiler and its insulation, but all of the separator piping going up to the condenser.
What was happening was the ammonia vapor was condensing in the separator piping and never making it to the actual condenser and therefore, there was no liquid ammonia going to the freezer.
The answer was to actually restrict the amount of air blowing in through the grate/hatch and voila, temperatures returned to normal.
I knew something was wrong when the boiler outlet temperature was at 120 degrees and the condenser inlet was 80 degrees, there had to be precious little ammonia vapor making it into the condenser and therefore available to cool the fridge. Whatever did eventually make it to the evaporator sections was keeping the freezer cool, leaving nothing left for the fridge.

I can't wait to download my data from my probes in the freezer and fridge to see what they were doing.

So, who would have guessed this as the problem?

[Buttercup]

Just got to our destination. Fridge is a perfect 40 degrees. Good nite everybody.

[perryg114]

Ok so was this what was wrong with your old unit as well?

Perry

[damonbeals]

So how did you limit the cooling, turn off the fan? Block some of the lower vents?

Damon
#4827

[Buttercup]

Yes, I put in a piece if thin MDF in the lower access door to block the full force of wind from passing through. It still lets some through and it seems that was all that was needed. I do believe that this could have been the problem with the old cooling unit but will never know for sure. All I do know is the rebuilt unit I installed was acting the same as the old unit until I took the corrective action.

[perryg114]

Expensive lesson. Keep the old unit. I.was having trouble believing that the old unit worked fine standing still and did not work while moving. Did you change the venting at some point?

Perry

[Buttercup]

Originally Posted by perryg114

Expensive lesson. Keep the old unit. I.was having trouble believing that the old unit worked fine standing still and did not work while moving. Did you change the venting at some point?

Perry

No, I am going to send it back. I'll get $100 for the return. I don't need one more piece of junk in my garage. Yes, it is probably a perfectly good unit and it was an expensive lesson but I would not have learned it had I not done what I did. I would have thought the new unit failed or of questionable quality and I would have been wrong. I really learned a big lesson on these units and I hope I can impart knowledge on to others on this cycle.
I am going to develop a training lecture for next years International Rally and help others with their fridge knowledge.

[KJRitchie]

Its hard to imagine too much cooling air could do this because most or us are trying to figure out how to install fans etc to get more air flowing to the vent. So ambient 70 degree air on your trip was able to cool the vertical tube that has the insulated aluminum covering enough to do this? What happens when the temperatures are in the 40s? Maybe we should block our vent door somewhat.

I"m glad you problem is resolved.

Kelvin

[perryg114]

My 30+ year old RM100 cools fine with no fans.

Perry

[Buttercup]

Originally Posted by KJRitchie

Its hard to imagine too much cooling air could do this because most or us are trying to figure out how to install fans etc. to get more air flowing to the vent. So ambient 70 degree air on your trip was able to cool the vertical tube that has the insulated aluminium covering enough to do this? What happens when the temperatures are in the 40s? Maybe we should block our vent door somewhat.

I"m glad you problem is resolved.

Kelvin

I know its hard to imagine, but it is the truth. With enough air flow,or really for that matter, enough cooling effect, you can cool all of that piping between the boiler outlet and the inlet to the condenser fins. You can cool it enough that the ammonia condenses to a liquid before it ever gets TO the condenser. And if it cools prematurely, it will turn into a liquid and fall back down never performing any cooling in the fridge, but cooling the weak ammonia solution in the boiler. Basically, the cycle extends only to the boiler and moisture separator sections and never really reaches the condenser fins and therefore is never turned to liquid ammonia for the freezer and fridge to use for cooling. In short, it can cool everything off right at the boiler. That condenser section is really a point of no return - if it condenses before that part, it will do no work in the fridge. But if it condenses properly IN that section, all that ammonia will cool the freezer and fridge sections as it should.

Allowing less airflow means that cooling of the moisture separator sections is minimised and therefore ammonia condensing takes place in the condenser, where it belongs and it does not cool prematurely in the moisture separators off the boiler outlet.

Frankly, when the boiler outlet is below 180 degrees with over 350 degrees on thermal input to the boiler, and the vapour going TO the condenser fins is less than 120 degrees, I know that subcooling is probably happening in the moisture separator sections and robbing heat from the boiler (and therefore from the fridge) and I have a less efficient operating fridge. It may work and keep the food cool, but it is using extra gas / electricity to do the job.

[cwf]

Howdy Buttercup.

Have you an estimate on the airflow? Is this a volumetric or velocity problem? Would you benefit from shielding an area of tubing from airflow?

[Gene]

This is quite a surprise and I'm glad you figured it out. I'm impressed with your thought process at finding the solution and wish I could understand all of it.

So far our fridge ranges from 39˚ (cold morning) to 41˚ (hot day), but has gotten higher on 100˚ days with the fridge side in the sun.

I've thought about adding a fan in the compartment, but haven't. Seems like a fan with a temperature sensor to turn in on and off depending on ambient temperature would be the best way to go.

Gene

[Jammer]

Can't you just put some insulation over the separator?