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Old 11-27-2011, 02:10 PM   #1
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Question Fridge is now a freezer

My Dometic RM2612 has decided to run full tilt, all the time. It drops to 20 degrees on gas and AC. It worked fine 3 weeks ago on our 7-day trip to Cumberland Gap.
This makes me suspect the thermistor in the plastic slide-sleeve is bad. I looked at the wiring diagram and saw that this is supposedly connected to a 3A fuse.
Questions: 1) Would anything else cause the over cooling?
2) Is there a fuse involved with the thermistor?
3) If the fuse blew (or is corroded) would an open circuit cause over cooling?

All help appreciated before I tackle this project,
Teach
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Old 11-27-2011, 06:12 PM   #2
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I kind of push the limits before I put my TT away for the winter actually picked it up in a snow storm what I have found when the weather is cold out the fridge works really good! I have to turn mine way down or it will freeze every thing it is a mechanical one though it is interesting that it over cools both on gas and 120v have a look at this maybe it will help--http://gasrefrigeration.net/dom_techdata/26121_2852SM.PDF
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Old 11-27-2011, 08:42 PM   #3
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I don't think the thermister has a 3 amp fuse just for the thermister. It is possible the thermister or wiring is an open circuit and the control board is running in "limp" mode (constant cooling)

Here is some info I got from a PDF on service tips for a 2612:

THERMISTOR
Disconnect the thermistor harness from the P2,
2-pin terminal on the lower circuit board. Place
the thermistor in a glass of ice water, approximately
33įF to 35įF. Wait 2 to 3 minutes. You
should get a reading of approximately 7,000 to

10,000 ohms.


The P2 connection is on the circuit board inside the black plastic box on the left side of the fridge (looking a the back from outside). If you take off the plastic cover there are 2 connectors on the left side of the circuit board, P2 is the only 2 pin connector.

Here is the URL above as a "clicky" - The info I posted above is from page 8.
http://gasrefrigeration.net/dom_tech...121_2852SM.PDF
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Old 11-27-2011, 09:50 PM   #4
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Quote:
Originally Posted by awellis3 View Post
My Dometic RM2612 has decided to run full tilt, all the time. It drops to 20 degrees on gas and AC. It worked fine 3 weeks ago on our 7-day trip to Cumberland Gap.
This makes me suspect the thermistor in the plastic slide-sleeve is bad. I looked at the wiring diagram and saw that this is supposedly connected to a 3A fuse.
Questions: 1) Would anything else cause the over cooling?
2) Is there a fuse involved with the thermistor?
3) If the fuse blew (or is corroded) would an open circuit cause over cooling?

All help appreciated before I tackle this project,
Teach

Teach

I found this under the RM2612 section. Does yours have a "manual mode"

Quote:
This refrigerator is equipped with a control system, which can automatically select the most suitable energy source which is available, either 120 Volt AC or LP gas operation. The refrigerator can be operated in either the AUTO mode (thermostat factory preset below the safe food storage temperature) or MANUAL mode (continuous operation - no thermostat control).

NOTE: Under certain cool weather conditions, the food in the lower portion of the fresh food compartment may freeze if operated for an extended period of time on the MANUAL mode.
And this

Quote:
MANUAL MODE
When operating in the MANUAL mode, the AUTO mode indicator lamp (A) will be off, and the refrigerator will run continuously on the energy source selected by the control system.

NOTE: The food in the lower compartment may be frozen if the refrigerator is left on "MANUAL" mode.

STANDBY MODE
This control system contains a feature that will continue to operate the cooling system in the event of a failure of a major operating component. If the control cannot read the temperature sensor and operate at the preset temperature, then the control will run the cooling unit like the MANUAL mode.

The refrigerator will continue to operate in this mode indefinitely or until a new sensor is installed and the system
is reset.
Mine does not have this "Manual" mode. Mine has "Auto" mode and "Gas" mode. But mine is an RM2652 a different model then your RM2612


Go to page 55 and 56 of this Service tech manual for the RM 2612 Sunline Coach Owner's Club - Sunline Owner's Files - Dometic Service Manual

By any strange chance do you have the fridge in "Manual" in place of "Auto"

Until reading this I did not realize they had some with an actual "manual" mode.

If it is not this then yes check the thermistor like Gene showed and check the connection on the PS board for corrosion.

Hope this helps

John
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Old 11-28-2011, 06:52 AM   #5
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I do have a manual mode and am not certain DW didn't engage it. I'll do some more investigation and let y'all know what turns up.
Thanks for the info and the tech advice.

Teach
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Old 11-30-2011, 07:53 AM   #6
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Originally Posted by JohnB View Post
By any strange chance do you have the fridge in "Manual" in place of "Auto"
Ah yes, the dreaded "operator error." I ran it overnight (empty) on gas and "Auto" mode. It didn't get down to freezing but did cool to 34F. Our nights are only in the upper 40's or lower 50s this time of year. I have camped with this trailer in cold weather and the refer's temp stayed right about 40 on those occasions.
Now, I recall reading in this forum that sliding the thermistor housing up or down can affect the temp. There is nothing in the manual about this. What's the scoop?

Teach
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Old 11-30-2011, 07:07 PM   #7
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Quote:
Originally Posted by awellis3 View Post
... Now, I recall reading in this forum that sliding the thermistor housing up or down can affect the temp. There is nothing in the manual about this. What's the scoop?

Teach
Here is the sticker I made for mine:

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Old 11-30-2011, 08:17 PM   #8
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Hey Teach, That was a fast fix and the easiest kind!!

Think of it this way, you could of tore apart the thermistor and a few other things before you backed into the manual button...

We all learn something from these things. In my case it was that some of the older units have a "manual" mode. Now what exactly one does with it I have not yet figured out.

Now to cool weather camping and the fridge, we cold weather camp often. I have found that if the camper itself is cold then the inside of the fridge is cold, like about 35 to 40 too. The fridge is satisfied it is close to temp before I ever turn it on and as such does not work much and will not freeze anything solid overnight. To help overcome this I add "unfrozen" ice blocks in the freezer and I put a gallon of room temp water in an old milk jug in the fridge to make the fridge work. Then it cools down and when we add the food the next day the fridge is already at temp. And the ice blocks are then froze solid.

You may also be fighting some of the lack of good venting behind the fridge. Before I added my fan kit up in the roof vent stack for the fridge I had temps of 34 to 36 as average during spring or early summer days. Come real hot summer it went up even more. By adding the fan in the stack I now get 32 to 33 no problem year round.

Loading it up may help get you started better.

Now to Gene's slider sticker.... He got me once on that as I have the same blue arrow but no sticker. And like you I have heard of sliding the thermistor up or down to change the temp. I even heard up was colder and that down was colder. So I tried both. I could not get it to do much better no matter where I put it. This was before the fan in the roof vent days. I had some much swing in the temp as it was I could not find any difference. Come to find out Gene made his sticker......

There may be something to what Gene found out as I think it actually does something on his. There is no mention of the slider moving to change temp in any Dometic repair manual that I have found. In fact they all state they are non adjustable unless you have the actual Dometic feature where you can adjust it on the control panel. They may be a level of heat stratification in the heat sink and by using that to ones advantage if you put the thermistor in the hotter area it should cool more. Which might line up with Gene's up being add more cooling.

When you try it, please report back.

John
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Old 11-30-2011, 10:21 PM   #9
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In all fairness, I don't think there is too much difference in temp with the slider. I think I tried it full up for a few days and full down for a few more days and watched my wireless remote thermometer. The temp will swing through the day and I looked at the max and min each day. As I recall, the max and min may have changed 3 or 4 degrees from full up to full down.

On another note, last February my home fridge died (and it was only 30 years old!!) so I fired up the fridge in the Sunline for a few days until I could get a new one delivered. Daytime outside temps were in the 40s and nighttime below freezing. The Dometic stayed about 32 to 34 the whole time and saved me from losing a lot of food.
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Old 12-01-2011, 09:08 AM   #10
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We all learn something from these things. In my case it was that some of the older units have a "manual" mode. Now what exactly one does with it I have not yet figured out.
The manual says there are three modes: Auto, Manual and Limp. The "manual" is used to freeze ice in the freezer faster. A problem you encountered. The "limp" mode is a fail-safe operation. If the control unit can't read the thermistor resistance, it goes into continuous operation.

So youse Yankees are saying that a temp of 32-34 degrees is normal for our refers when the trailer is sitting unoccupied overnight? 'Cause that's what I'm getting.

Kepp those cards and letters coming,
Teach
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Old 12-01-2011, 01:00 PM   #11
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So youse Yankees are saying that a temp of 32-34 degrees is normal for our refers when the trailer is sitting unoccupied overnight? 'Cause that's what I'm getting.
I was mistaken. It's down to 25 in the fridge. Called Dometic and got the thermistor specs for my control unit. At 32F it should read 8500-9500 ohms. I'll be at it again.
Oh, and as a point of interest, she asked me where my slide was; up, middle or down, so apparently it does make a difference.

Still workin' at it,
Teach
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Old 12-01-2011, 07:29 PM   #12
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Yup, 32 to 34 would be a normal range. I have seen a minimum of 29 and a maximum of 40 on mine at different times in the summer.

Remember to unplug the AC and turn off the fridge before checking the thermister.
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Old 12-04-2011, 09:47 AM   #13
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Quote:
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Yup, 32 to 34 would be a normal range. I have seen a minimum of 29 and a maximum of 40 on mine at different times in the summer.
Remember to unplug the AC and turn off the fridge before checking the thermister.
Heck, I unplgged the DC, too. I know how fussy these circuit boards can be.
Alrighty then, here's the rest of the story. Armed with my 9000 ohm reading, I call Dometic and get the really young-sounding missy on the line who thinks it is still an operator problem, and - guess what? She was right, sort of.
Confident of the thermistor and unwilling to give up on my two-year-old control board, I delved further into my testing procedure and asked myself if the refer wouldn't test more "real world" if it had something in it to cool. I put two room-temp, filled, gallon water jugs in yesterday a.m. Ambient temp inside the trailer rose to 62F and the refer cooled down to 38F by supper time. Overnight, ambient temps dropped to 34F in the trailer, but the refer was at 36F this morning.
Conclusion: Testing the refer empty causes its own problem with the temp control - probably relating to feed back time and ... whatever. Original problem = operator error. Perceived problem = faulty testing protocol.

Live and learn,
Teach
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Old 12-04-2011, 12:43 PM   #14
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Teach,

Glad things worked out. Yes I can see in cold temps trying to cool down a fridge with nothing in it can create temperature variances. And it looks like you just proved it!

In the summer you are at least loosing some cooling through leaking door gaskets or even through the insulation so the fridge is working to some level even if empty. But in 34 F ambinet temps it does not have to work much at all. And yes 2 gallons of approx 68F water to be cooled down to 34F is a heat load...

Another question, do you use internal fridge fans? I have 2 of the little battery operated Camco fans to stir up the air. I'm sure that air movement is better then just convection on a cold winters day inside a well insulated sealed up box... I even put mine in the when I turn the fridge on the night before.

Thanks for reporting back. Now we all learned something.

John
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Old 12-04-2011, 09:48 PM   #15
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Another question, do you use internal fridge fans? I have 2 of the little battery operated Camco fans to stir up the air.
I have one in my pop up's small fridge. I also have installed a computer muffin fan in my pop up due to the lack of a sufficient stack. It blows up onto the piddling coil that passes as a condenser.


I haven't needed either fan in my Sunny. The refer in the Taj kept contents at 40F in 99 degree heat.

As a side note. Don't y'all think it borders on miraculous that a propane flame can make ice? Sort of answers the old question, "What is man that Thou art mindful of him ...?"

Teach
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