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Old 02-02-2007, 05:19 PM   #1
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1986 31' Sovereign
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Refrigerator Help!

Howdy all,

My Dometic RM 2800 is acting strangely. Freezer temp is 8 deg fahrenheit (as it should be) BUT refrigerator section is 58 deg f which is 23 deg +/- too high.

Searched the forums. Looked at many rebuilder websites. Have a theory, looking for comments...

1. Freezer temp indicates that cooling unit and thermostat are operating within normal limits.

2. Looked at install instructions for cooling unit -- all refer to a mastic that is applied to the back side of the refrigerator cooling fins during the install process.

3. So -- could the mastic in my 10 yo reefer be dried up and/or shrunk to the point that the cooling fins are isolated from the cooling tubes?

4. Or am I missing something painfully obvious?

Thanks for any help,

Mike
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Old 02-02-2007, 05:24 PM   #2
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May just be painful...

Mike-

Some of the Dometic's cool first in freezer and take a while for refrigerator section to get cold, if they've been sitting unused for a while (months..). Did you let it run for 3 or 4 days with no change?

Unit might have partial obstruction or air bubbles in cooling tubes at refrigerator section. Search on "burp" and "refrigerator" for possible treatments.

If those fail, may be cooling unit uitself, rathr than mastic. There are shops that can furnish replacements, or you could ship refrigerator to them for rebuild, which might still be easier and cheaper than new one. search for "cooling unit replacement" or "cooling unit rebuild". Many RV repair shops will be tempted to just sell new unit, since that avoids for them potential liability of rebuild fails, and is easier.

Good luck...
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Old 02-02-2007, 06:45 PM   #3
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Here are a few things to look for:

It's very possible that you have a slight blockage in the lower absorber coils or the low temp evaporator section. The 'burping' that is often referred to 'might' help, but only on a temporary basis, as the blockage (if it exists) will only be moved around inside the tubing to manifest itself again later.

Feel around the back of the cooling unit. Temps should be evenly warm to hot on the absorber coils, the accumulator tank and the boiler tube. If they are not, it is a sign of a blockage.

Thermal mastic rarely dries out, so the possibility of that happening is small. OTOH, if it was not applied properly before the cooling unit was installed, that would be cause for alarm. It is impossible to tell unless you remove the cooling unit from the box to check.

Your unit should have a thermistor on the cooling fins in the refer section. It is entirely possible that it is not functioning properly. There is a test to determine this, but you will nees a very accurate thermometer and a good multimeter. The test is a bit lengthy and involved, so PM me if you would like to attempt this.

Also, is the unit doint this on LP AND electric, and have you tried to run it on both (assuming of course that it HAS both ).
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Old 02-02-2007, 07:44 PM   #4
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Thanks for the help. guys.

The refrigerator is doing the same thing on gas or electric. I know it is sick because we did a 5 month 4500 mile road trip last Spring/Summer and the unit worked great in temps similar to what we are seeing now at home (80's, low humidity)

It seems likely that tube blockage is the most likely suspect.

The question then becomes, replace the cooling unit or the whole thing.

Be nice if the lottery panned out...

Thanks again,

mike
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Old 02-04-2007, 02:22 PM   #5
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Boring Update

Well, the burping process is complete with no success. Freezer compartment chilled right down to 10 deg/f but reefer is at 60.

Did some digging and determined that PO replaced colling unit with rebuilt 27 months ago.

So the only decision remaining is another rebuilt cooling unit or a new refrigerator.

Thanks for the help.

mike
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Old 02-04-2007, 05:59 PM   #6
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Re-builts are far cheaper than a new box, and they are not that hard to change out, but you DO get a 3 year warranty with a new Dometic refer.

tough choice...................................
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Old 02-05-2007, 08:44 AM   #7
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fridge woes

try a simple test first before you rebuild.put a thin layer of vaseline on the door seal around the door.The seals get to the point they will not seal tightly any more.It worked on our 73 that we used to have. It would freeze in the freezer and cool in the box to about the mid 50's. After the vaseline it coled to below freezing in the box if we wanted it to.
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Old 03-26-2007, 09:20 AM   #8
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Doors

Kind of a late post, but I've found the worst thing I have been doing is leaving the doors slightly ajar in an effort to pervent mildew when I'm not using the trailer. Search for the posts on swolen doors - this is what they do if unrestrained. I had to disassemble the doors and use the posted proceedure to get them to close all of the way. The old $1 bill test indicated I really didn't have a problem but it wasn't the seal holding on to the bill, it was the swollen interior. By cleaning and drying the interior and keeping the doors completely closed, my doors now seal and the temps stay where they should.
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Old 03-26-2007, 12:59 PM   #9
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Quote:
Originally Posted by HiHoAgRV
Kind of a late post, but I've found the worst thing I have been doing is leaving the doors slightly ajar in an effort to pervent mildew when I'm not using the trailer. Search for the posts on swolen doors - this is what they do if unrestrained. I had to disassemble the doors and use the posted proceedure to get them to close all of the way. The old $1 bill test indicated I really didn't have a problem but it wasn't the seal holding on to the bill, it was the swollen interior. By cleaning and drying the interior and keeping the doors completely closed, my doors now seal and the temps stay where they should.
I have had a similar problem with my Dometics and the following is a history of what I have attempeted to date.

My box will cool down to a good operating temperature when first started but the long I am on the road the warmer the box gets until it is operating around 50 degrees F. This take about 4 to 5 days.

Having talked to Dometic they commentd on Airstreams large opening behind the box. The Dometic installation manual calls for no more than 1 in. of clearance against the back of the ref. With that in mind I removed the box and installed a sheet metal wall to create the chimeny Dometic wanted. Also while the box was out I made a pillow like assembly along each side of the box to insulate the sides from the 100 degree plus air that is common around the box in the summer. You can see the sheet maetal work the insulation was installed forward of the silver tape but now in place for this picture. The insulation was covered with a plastic sheet to allow the box to slide in and out without pulling the insulation out but maintaining a good contact with the sides of the ref. Neither effert has shown great results.
In the past I had installed a fan to cool the coils and force air up the back but that did not work.

I am very interested in HiHoAgRV's comments about the door being left open and would ask him to give more details about the proceedure he used.
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Old 04-04-2007, 10:10 PM   #10
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swollen doors

I had similar issues, the freezer was fine, lower section - unpredictable at best (wifes response to warm milk and eggs, very predictable and unprintable). A search of the forum suggested I close a dollar bill at various places and see if there was a drag when I removed it. Everywhere I tried it, there was a definite drag, supposedly indicating the gasket was making contact. I finally noticed I could see a gap where the gasket was not even touching but the dollar still had drag and no matter how hard I pushed the door closed, the gasket would not touch. I found a fellow forum member had a similar issue with his door not closing and posted the method he used to get the doors to fit. I did a search and can't seem to find the string. The problem is how the doors are made, a thin plastic shell is filled (overfilled?) with foam and given a good chance and time, the stuff continues to swell years later and distorts the interior of the door to the point it won't close. Basically, remove the doors and take off the front panel. Use a hack saw blade and cut a slot from the front around the perimeter all the way to the back side of the interior plastic. Remove a small amount of the insulation and test fit the door. Repeat untill the door will fit all the way and the gasket touches. Fill the slots with caulk, refit and let the caulk harden. Now the doors will close all the way and the fridge works much better. Don't leave the doors open and the swelling can't reoccour.
Hopefully a moderater or super member can sluth the original string, I don't do the method justice.
The other inprovement was an internal and external circulation fans, well covered in other posts.
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Old 04-04-2007, 11:14 PM   #11
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If you keep the reefer door(s) closed all of the time when the AS is in storage, how do you keep the interior of the reefer from getting "stinky?" I've always heard the door should be stored open to prevent mildew, etc. Am I missing something?
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Old 04-05-2007, 02:54 AM   #12
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Quote:
Originally Posted by wbrownrr
If you keep the reefer door(s) closed all of the time when the AS is in storage, how do you keep the interior of the reefer from getting "stinky?" I've always heard the door should be stored open to prevent mildew, etc. Am I missing something?
I was wondering the same thing. Ever since I was kid and dirt was new. I remember my dad leaving the refer door open a crack so the refer won't mildew or get stinky. I do the same now and haven't had any problems other than the 40 yr. old gasket getting a bit stiff. BTW, I use the original Dometic in my 1965 Caravel. Which will still freeze everything in there if you turn it up too high.

Quote:
Having talked to Dometic they commentd on Airstreams large opening behind the box. The Dometic installation manual calls for no more than 1 in. of clearance against the back of the ref. With that in mind I removed the box and installed a sheet metal wall to create the chimeny Dometic wanted. Also while the box was out I made a pillow like assembly along each side of the box to insulate the sides from the 100 degree plus air that is common around the box in the summer. You can see the sheet maetal work the insulation was installed forward of the silver tape but now in place for this picture. The insulation was covered with a plastic sheet to allow the box to slide in and out without pulling the insulation out but maintaining a good contact with the sides of the ref. Neither effert has shown great results.
In the past I had installed a fan to cool the coils and force air up the back but that did not work.
I did also put baffles behind my refer to direct the airflow and eliminate the dead air space. Between the burping and vastly improving the airflow, I have a 40 yr old refer that works just fine. I also put the fans in and it made only a 10 degree difference when they are on. Probably worth it on really hot days, but other than that, no.
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Old 04-05-2007, 07:52 AM   #13
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To avoid the dreaded rotten refrig, I make sure it's clean and DRY before closing it up. I usually wonder out to the camper a everyother week or so and as a habit open the doors and check on things. I've left the doors open on newer units, but these old Dometics seem to swell up with time and perhaps extreme temerature changes.

It works for me
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Old 05-29-2007, 07:15 AM   #14
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How level?

Hello, saw your post on keeping fridge level-I see by your info you are a professional/expert on RV cooling!

Had a problem this past weekend, the fridge in our 89 Excella always worked fine, this weekend while boondocking, the freezer was very cold, the fridge was not cooling well at all. I thought we were pretty level, had plenty of propane, etc so I was a little stumped; why the freezer but no fridge?

When we got home I set up in the driveway, checked that the camper (and fridge) were level. I did find out that the level mounted on my camper was not calibrated perfectly, so we were probably off 1-2". After leveling, I let the fridge run on propane for a while and everything seemed ok.
Is it possible that being 1-2" off level was causing the fridge to run warm?
Yet the freezer still worked fine?
Aren't they cooled by the same motor?

Thanx, Bill
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Old 05-29-2007, 09:11 PM   #15
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[quote=BillTex Hello, saw your post on keeping fridge level-I see by your info you are a professional/expert on RV cooling!

Had a problem this past weekend, the fridge in our 89 Excella always worked fine, this weekend while boondocking, the freezer was very cold, the fridge was not cooling well at all. I thought we were pretty level, had plenty of propane, etc so I was a little stumped; why the freezer but no fridge?

When we got home I set up in the driveway, checked that the camper (and fridge) were level. I did find out that the level mounted on my camper was not calibrated perfectly, so we were probably off 1-2". After leveling, I let the fridge run on propane for a while and everything seemed ok.
Is it possible that being 1-2" off level was causing the fridge to run warm?
Yet the freezer still worked fine?
Aren't they cooled by the same motor?]

Bill,

Just a quick tutorial on RV absorption refrigeration. There is no motor or compressor like household units have. There are a mass of tubes filled with ammonia and hydrogen, and a bright yellow anti-corrosive called sodium chromate.

This solution is heated in the boiler section, above the propane burner or by the electric element also located in that section. The solution rises to the condensers at the top, and the cooling process begins (I can explain exactly what happens, but it is very lengthy, PM me if you're interested.)

The solution then proceeds to the low temperature absorber, and then down to the high temp absorber. This is where the heat transfer from the box takes place, and the freezer and fridge sections get cold.

The solution then continues downward to the leveling chamber, or accumulator, and the process starts again.

New units need only to be level to the point that the RV is comfortable to walk in. Older units need to be 'LEVEL', that is to say, bubble level! Since gravity plays such an important role in the cooling process, you can see why being level is so important.
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Old 05-30-2007, 07:03 AM   #16
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Thanx for the fridge education Lew!

Is it likely there would be a difference in performance on propane vs electric?

I have only run propane for maybe 1 day at a time before and that is usually while towing, this is the first time we ran 4 days while stationary on propane. By day 2 it was noticeably warmer...

I am pretty sure it was a matter of levelling; we were about 1" off port/starboard and 1-2" off bow/stern. Maybe this combo was just enough to cause problems?

Never worried as long as we were within 1" or 2" before, but we are usually running on AC, not LP, and the beer was always nice and cold...

I have added a carpenters level to to my tool box and will dial it in more precisely next time (frame, fridge, etc) we are boondocking. I should have calibrated my AS level before, it never occured to me it could be off as much as 2"!

Thanks for your insight, Bill
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Old 05-30-2007, 07:41 AM   #17
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Bill,

I forgot to mention maintenance. It's a good idea to either clean, or have someone clean the LP burner parts of the fridge. The can and do get rusty and if not properly functioning, will degrade the performance.

A very overlooked part of the fridge is the spiral baffle. If you have a manual and check in it, you will see that it is a rectangular piece of sheet metal twisted in a spiral pattern. This VERY IMPORTANT piece resides INSIDE the flue tube, also located directly above the LP burner section.

It is suspended by a precise length wire and often gets rusty and or eaten away by rust. This little piece could also be responsible for degrading the performance of your fridge. The only down side to this comes in trying to remove it to clean it.....usually involving complete removal of the fridge. It IS accessible in some trailers (like mine) thru the upper fridge vent door.

If your unit is working well on electric, then this test is not necessary, but I usually will open the control box at the back of the fridge, find the 2-1/4" push connectors that come from the 120VAC heating element, remove them (mark which color goes where) and will make a pig-tail connector and plug the fridge electric element DIRECTLY into a 120VAC outlet.

I then run the fridge, having effectively removed the controls from the picture, and see what the unit does. After running overnight, it should be VERY COLD in the freezer and nicely cold in the fridge. Remember, you have no temp control during this test, so don't leave anything in the fridge that might freeze, 'cause it might freeze!

Good Luck!
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Old 06-19-2007, 01:15 PM   #18
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Quote:
Originally Posted by lewster
[
New units need only to be level to the point that the RV is comfortable to walk in. Older units need to be 'LEVEL', that is to say, bubble level! Since gravity plays such an important role in the cooling process, you can see why being level is so important.
Hi Lew-can you define "older"? As far as I know my 89 has original fridge. I finally broke down and brought it to the local dealer ($).
They have been running it over night and so far they have the same results as my test; cold freezer, warm fridge.
So I may be faced with replacing my fridge...

Any further advice?

Thanx, Bill
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Old 06-19-2007, 08:54 PM   #19
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I'll have to check the specs for your unit....what is the model #?
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Old 06-19-2007, 09:33 PM   #20
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Thermocouple

My old Argosy had a unit in it that had the same problem and I found that the thermalcouple was touching one of the cooling fins. I moved it away and wala - no more problem.
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