3 year old Dometic doesn't work

[doorgunner]

Kimber;

A better placement of your "finger" on the thermometer may help!!

whaaat. Drive safe.

I stumped also.

[NevadaGeo]

Tim, I haven't seen numbers on someone checking the refer freon coolant level/pressure. I'm sure you did it tho.
I had a drill rig once get a rock that would float in the air standpipe, the driller could not find why he couldn't get any reverse circulation off bottom of the hole, until they took the top head off and managed to blow the rock out. It would float up and block the exit of the pipe, but fall down when they were looking for it. Maybe a floating blockage right at the exchanger oriface. (Probably way off on nomenclature there).
Perry

[Luminati]

Tim...you need this special tool to fix that damnetic! -Karin

[Mexray]

Tim, if all else fails...

Boat drinks
By: jimmy buffett 1979


Boys in the band ordered boat drinks
Visitors scored on the home rink
Everything seems to be wrong

Lately, newspaper mentioned cheap air fare
I gotta to fly to saint somewhere
Im close to bodily harm

Twenty degrees and the hockey games on
Nobody cares they are way too far gone
Screamin boat drinks, something to keep em all warm

This mornin, I shot six holes in my freezer
I think I got cabin fever
Somebody sound the alarm

Id like to go where the pace of lifes slow
Could you beam me somewhere mr. scott?
Any ol place here on earth or in space
You pick the century and Ill pick the spot

Oh I know, (I know)
I should be leaving this climate
I got a verse but cant rhyme it
I gotta go where its warm

Boat drinks
Waitress I need two more boat drinks
Then Im headin south fore my dream shrinks

I gotta go where its warm (I gotta go where its warm)
I gotta go where its warm (I gotta go where its warm)
I gotta go where its warm!

I gotta go where there aint any snow
Where there aint any blow
cause my fin sinks so low
I gotta go where its warm


Tim...forth verse seems to be one answer to your problem...

Wow, you've got a bundle of things going on with your cooler/warmer...

To my way of thinking, if it works when stationary, it should work when on the road...so, I'd really check around for something that's disturbing the burner or flame propagation...or disturbing the proper airflow up and over the coils...do you have any unusual fixtures on the roof, around the frig vent that might be screwing up the 'normal' venting process??? Have you checked to see if you have a big mud wasp nest inside the roof vent??? I found one in ours when we first bought it - it was blocking almost half of the vent!!! Just some thoughts...

Road 'bounce' should promote proper gas/fluid flow through the cooling system - provided the burner/flue is working properly...again, that's where I'd concentrate my 'search'...burner airflow when moving...

I also don't think the axles are a contributing factor...our 28 footer has it's original frig that works really great, on, off, the road or upside down, maybe...AND I've put those same #3500 new axles on our rig last year - and in fact, the 'ride' is much 'easier' when compared with the old 'stiff' axles...in about five trips on the new axles, I haven't noticed any evidence of 'motion sickness' in the AS's construction - loose rivets, etc...

I bought one of those fiberglass 'funnel' shaped manifolds that you mount over the upper coils - and has a muffin fan in the top that's controlled by a thermostat...As you have to remove the frig to mount this rig, and the frig continues to work great, I haven't made the effort yet to install it! However, it does look like a good way to improve the air flow in an Airstream's cramped ventilation quarters...a project for a future date...!

Good luck on your mystery...let us know when you solve it...

[Buttercup]

You all are so funny! Karin - if I had that tool, I bet it would be fixed from FEAR! Wow!!!

Mexray, I have a feeling that when the boiler is warm but the outlet to the condenser is not, that also indicates a circulation problem. A hot boiler means that the flame is on and running but ammonia is not moving, right? I am no expert but learning more and more every day!
However, I believe that what Perry says may be a thought... But what could be plugging the pilot tube inside the boiler??? And how does it get free when the unit is off and all thawed out?

I am going to call Dometic again. I saw another '77 with #3500 axles like mine and the same fridge with no problems at all. So perhaps it is just the unit that is bad. New doesn't mean that it is good, does it?

[Gene]

I'm thinking that no matter what you do, that refrigerator will not work properly. There's something wrong with it that can't be fixed without taking the whole thing apart and finding the beer can stuffed in there or whatever may be screwed up. Only if Domestic replaces the whole unit or rebuilds it completely, will you have satisfaction.

Gene

[Buttercup]

Well, I have been working in this problem still and have had no real progress to speak of. If you read through my first post in this thread, you will see what the basic problem is. Read the whole thread and you will see what I have done so far to try to diagnose the problem.This isn't a simple "my fridge ain't cooling" thread.

After reading all of that (if you do) you may question why I would bother to do one minute more of testing and/or general messing around. The simple answer is that the cooling unit works – and this I proved this weekend with a simple test suggested by a company who would be happy to sell me a new cooling unit, but doesn't want to IF mine still actually works.

Last year before going to the International Rally I contacted a company that we mentioned in the Vintage Advantage Newsletter in a story written by Michael Depraida. His experience with this particular company was far better than mine. Weeks after placing my order for a new unit, I learned that it had never shipped and time was running short to replace the cooling unit. After a few more weeks the company said that they would “Overnight” the unit to me at their cost because it was their fault that it never shipped in the first place AND I was trying to get this done prior to leaving for International. But, alas, the unit was not shipped when the owner of the company caught wind of what the costs of shipping the unit actually were. The unit was not shipped. We'll talk later perhaps about the fun we had getting our refund back!

So, with no properly working cooling unit, we turned on the fridge and loaded the fridge with food. 2 days later, as expected the fridge stopped working within a few hours of hitting the road and did not properly start working again until AFTER we turned it off and fully let it thaw out. Yes, some food was lost but most survived in the cooler we brought along with us.

This last few days I have been doing more research and testing of our fridge. One item I discovered was that our gas pressure on our trailer was a little too high. The fridge requires a minimum of 7 inches of water at the burner, 11 is the normal pressure. I measured the gas pressure and found it to be about 13 inches. Although my pressure was a little high, it was not so high that it should have impacted refrigerator operation. I lowered the pressure to about 11 inches with no load on it and it drops to about 10 inches with the stove burners running fully.

Per the recommendation of the company I am now ready to do business with I did a “Bypass Test” to check the performance of the fridge. The test involves simply bypassing the thermostat controls on the fridge (not the safety controls mind you) and running the fridge while monitoring the temperatures of the inside and outside.

The process of bypassing the thermostat simply involved unplugging the thermistor from the control board that runs the fridge. A thermistor is simply a resistor that changes its output based on the temperature the resistor is exposed to. This cannot be done with an older fridge that does not have electronic controls. With the thermistor unplugged the fridge does not know what temperature the fridge is at and just runs. As long as the flame doesn't snuff out or the boiler doesn't exceed the temperature set by the limit switch mounted on the site the fridge with run.

I started the test running on gas at about 3:00 p.m. and checked its progress every couple of hours. The result, as expected – the fridge worked – damned well I might add. Within 1 hour the freezer was frosty and within 4 hours the fridge temperature was dropping nicely. Outside, the temperature as felt by hand of both the boiler and the absorber coils was warm and lukewarm respectively indicating very good circulation throughout the unit. I let it run overnight just to see what it would do. When I checked it in the morning I discovered the freezer to be frosty cold and the fridge to be at an impressive 13 degrees Fahrenheit.

Obviously, the bypass test was a success – but the trailer was standing still. Tomorrow we will hitch up and drive drive around for a few hours to see what happens and look at how long it takes to fail and also perhaps try to see where the failure occurs within the cycle. It would be a nice surprise if for no reason it started working – maybe that little adjustment in gas pressure somehow did the trick.
We'll see.

[NevadaGeo]

So there might be a loose connection or intermittent short in the system, pointing to the thermistor area. If it shuts off on the drive, try the drive again with your thermistor bypass going.

[Aage]

Are refers like the furnaces (boards go out regularly)?

[Buttercup]

No, it doesn't shut off as evidenced by the hot boiler column. It still has thermal input. When I do our test tomorrow i will be in bypass mode again, so the gas valve will stay open even if the fridge is at the proper temperature.

[Aage]

Sorry, I think I should have been more clear. By "go out", I meant "fail".

[Buttercup]

I am sure boards do go out. However, I see no indication that the board IS going out because if the cooling unit itself was working, the board would either shutdown altogether, in which case the boiler and absorber pipes would all be cool and the interior would of course thaw out. If the board fails and just leaves the gas valve open then assuming the cooling unit works the fridge would just get colder and colder, freezing the food as my bypass test shows. But even in that case, as shown by my bypass test, the boiler and absorber coils were warm, not too warm - maybe more on the cool side and were both about the same temperature, which is indicative of proper circulation.
Remember, with these fridges, whenever there is a great differential between the boiler and absorber you have an indication that there is either a loss of circulation (absorber coils will be cold with a hot boiler) or a loss of hydrogen charge (boiler will be much cooler than the absorber coils).

Originally Posted by Aage

Are refers like the furnaces (boards go out regularly)?

[Buttercup]

Looks like my 2nd test is already showing some problems before it is ready to start fully. I loaded the fridge with water bottles in the freezer and the fridge to "load it up". Started the fridge up again and I am getting completely different results and a surprise that totally points to a failed cooling unit!
The freezer froze, but the fridge would not come below 40 degrees and the boiler was hot while the absorber coils were still cool. This points to a plugged system. BUT I am going to do a final test after thawing out completely. This will be a bypass test on electric unloaded and loaded.

[HowieE]

While my frig is not falling short of expectations as much as your I too have never been satisfied with it.

In general it will only cool the frig side to about 40 degrees below ambient. That's fine in cooler weather but not so during the summer. In fact in winter the frig can start to freeze liquids place close to the fins.

I have modified several things in an attempt to improve the efficiency. I pulled the box and added insulation between it and the side wall to remove the ambient load off the sides. I installed a sheet metal false wall behind the unit to provide the 1 in. clearance Dometic requires in the manual. I installed the fan assisted coil mode on the rear. i have a small fan inside the frig to aid circulation. None of these modes had any measurable effect on the operation.

I had come to the conclusion that Dometic just does not make a product that is capable of providing what I was looking for.

As far as the question of level is concerned I would assume, and have always used this practice, that if the coils still have a negative angle, to return the gas, the frig should operate. I have never found this not to be true.

[lewster]

By 'bypassing' the thermistor, you are essentially running the cooling unit wide open and should have a continuous flame on LP or constant 120VAC to the heating element. Expect the temps inside the unit to be well below 20ºF in the freezer section (which has no controls anyway) and usually well below 32ºF in the fridge section as there are separate evaporators for each section.

You can also test a thermistor with a glass of ice water, thermometer and an ohm meter to compare the resistance from the thermistor with a table of known values at specific temperatures.

Good luck with your test!

[HowieE]

Lewster

You mention a separate evaporator for each section. While I have not replaced the cooling unit in this frig my last one I did and it looked like there was only a convection connection, aluminum plate to the fins, between the freezer and the frig side with the thermister in the frig section.

I just assumed the unit cycled against the frig section and it had a 100% duty cycle if the frig was above the set point. I would love to get a cooler frig section in the summer but have run out of ideas.

[lewster]

Originally Posted by HowieE

Lewster

You mention a separate evaporator for each section. While I have not replaced the cooling unit in this frig my last one I did and it looked like there was only a convection connection, aluminum plate to the fins, between the freezer and the frig side with the thermister in the frig section.

I just assumed the unit cycled against the frig section and it had a 100% duty cycle if the frig was above the set point. I would love to get a cooler frig section in the summer but have run out of ideas.

If you look at a working diagram of a gas absorption cooling unit, you will see 2 sections marked 'low temperature evaporator' and 'high temperature evaporator'. The low temp section is in back of the freezer section and the high temp section is connected to the fins of the refrigerator section. The difference being that the cooling solution (liquid ammonia coating the sidewalls of the evaporator sections which when coming in contact with the hydrogen gas creates a chemical reaction of intense cold) looses some of it's reactive abilities as the ammonia drops in the tubing from high to low temp sections.

In a nutshell (and to finally answer your question ), they are 2 separate sections but are joined together with many tubing sections which would not allow a separate, higher capacity high temp evaporator to be installed.:

I DO have a fix for anemic fridge temps though. I have been using 12VDC computer fans in gangs of 2-4 situated under the roof vent to pull ventilation air across the condenser fins to keep it within it's normal operating temperatures. It's this condenser that gets overheated and throws a wrench into the absorptive cooling process. Keep the condenser 'cool' and you will have lower fridge temps....especially in high ambient temps.

[HowieE]

Lewster

OK you have defined my next project. I think I will mount 4 or 5 on a piece of sheet metal and connect them to one or two adjustable thermostat mounted behind the unit. Then hunt for the point to turn the fans on. I would like to have the thermostat set about 10 degrees apart and each having about a 10 degree difference between on and off.

During cooler weather convection should still work even with the reduced opening. As the ambient goes up the fans would come on 2 and then 5

What do you think?

And could ventilation be Tim's problem while on the road. A possible down draft forcing heat retention behind the frig rather than exhausting it.

[lewster]

Howie,

I think you are over complicating it. K.I.S.S. if you know what I mean. I use 4 on large motor homes with the 12 cu. ft. Norcolds and they work great. Connect to the 12VDC block at the back of the fridge for power, run thru a fuse and use an SPST switch (mounted inside the trailer if you like) and that's all you need. The fans are so quiet that they can actually run continuously if necessary in very high ambient temp situations.

And yes, Tim might be getting a downdraft when traveling. I'm sure that the fans would help his situation also.

A while back, there was a kit available from Stu Snyder that tried to accomplish increased air flow, but it also used a plenum and single very small fan. It still pushed the air over the condenser instead of pulling it. I installed many of these and while they did help a bit, they were never the final solution. Multiple pulling fans just might be the answer.

[KJRitchie]

I've been reading this thread with interest because my 2008 Classic 25fb we just bought about a month ago experienced this on our first extended trip. Our fridge is the Dometic 3762 2 way. I'm having issues with my converter not charging the batteries at 13 v while on shore power but I used a charger to keep the batteries topped up on this trip.

I had the fridge on Gas during the time at camp to test out the LP system. The freezer compartment seems to be level with the floor adjacent to the fridge. At setting 4 (1 through 5) the temperature displayed on the fridge was 38F. The weather had been cool in Missouri but on Sunday the weather had cleared and the temperatures got into the high 70s low 80s. The fridge seemed to maintain temperatures or maybe it got up to 40 deg. The trailer was in the full sun. We even ran the AC inside to learn and test it out. (Unfortunately we have that dreaded problem with water leaking inside the interior from the AC, another story for other threads)
We broke camp on Monday around 11am to start the 350 mile drive home from Missouri to Dallas, TX. The wind was blowing strong out of the south so most of the time it was a headwind. For a period of about an hour on I40 its a crosswind with the street side of the trailer getting the wind and that is where the fridge is located. We stopped for lunch at a rest stop and my wife made lunch. I didn't notice the temperature reading because I didn't know there was going to be a problem. The wife knows not to keep the door open long when getting food out the fridge.

When we arrived home and the trailer was in storage I checked the fridge and it was at 54F. It was about 80 degrees. I checked the LP flame and it was hot and the flue part was too hot to touch.

Earlier you mentioned touching parts A and B and they should feel about the same hot to touch. I'd like to try that too. Can you post a link to the Dometic document that shows this troubleshooting test. My fridge documents down show that procedure.

When I had the Dometic recall performed this week, I talked to the RV tech about this issue and he said traveling shouldn't be a problem with the movement. He did mention that air coming across the top vent can cause flame outs and exhaust issues and my AS has a fence between the AC and the fridge vent on the roof. Here is the interesting thing he said about RV fridges. He says that a certain percentage of them have an issue with cooling while traveling. He couldn't explain the cause.

I'm admire your tenacity with this problem but by now I would've bit the bullet and bought a new fridge. I may be forced to go this route and if the if it still doesn't work while traveling I'd be forced to sell my AS with this disclaimer and take a big loss.

Kelvin