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Old 10-04-2011, 04:37 PM   #1
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Ye Olde Busted Fridge, part one

So we bought a used one for the '73 from a fellow forum member just about two years ago. It's a Dometic NDR 1062 out of a 2000 Airstream bus. Price was right at $400 and the wood front matched all the new wood we're putting in our interior re-do. The seller was a little "cadgy" about why he replaced it in the first place, but that's ok, everything seemed to work. It even has an icemaker. Susan really liked that part.

Naturally, it worked one season and died. Well, sorta died. Freezer works now, but the fridge area won't get below about 50 degrees. Did a bunch of reading here on the forums and was convinced the cooling unit was bad due to blockage in the pipes back there. So we struggled thru season two with the freezer and ice chests. Now trying to figure out what's wrong.

More in a few minutes. Be right back.

Jim
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Old 10-04-2011, 05:07 PM   #2
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I was swapping ideas over the past weekend with another forum member, Lothlorian (thanks Brian!!!) and he gave me the website and phone number to an RV fridge repair company in Alabama. I dutifully called Monday and spoke to the owner. He says, "Well, do you want me to send a new cooling unit or do you want to troubleshoot?" Since there was 500 somolians on the line, I chose option B, let's troubleshoot. We went thru the standard set of question. Any leaks (yellow residue). Nope. Circuit board seem ok? Near as I can tell. Yada, Yada.

He suggested that I disconnect the thermister and see if the fridge area starts to cool down.

CAUTION, WARNING, DANGER WILL ROBINSON. PROCEED FURTHER AT YOUR ON RISK.

The thermister in an RV fridge is basically an electronic thermostat with the probe on the inside of the fridge area that goes thru the wall of the thing and plugs into the circuit board. In my case, the board is on the back of the fridge at the bottom. The idea here is that once you unplug it, the heating element is now "always on" (regardless whether it's on gas or electric). Hence the warning above. I tend to get a little wimpy when it comes to glowing objects inside the camper.

Idea here, of course, is unplug the thermister and leave the heating element on, always on, for many hours and see if both the freezer and fridge are cool to normal levels. Guess what, it worked.

Jim
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Old 10-04-2011, 05:16 PM   #3
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I suppose I've read a couple dozen threads here concerning fridge problems and I've never run across this possible fix. Most times it seems, when people have a cold freezer and warm fridge, they simply replace the cooling unit on the back and move on. Problem always attributed to a "blockage" in the coils.

So I guess the question is, has anybody ever actually fixed the warm fridge/cold freezer simply by replacing the thermister? My first thought is that is too simple. My second thought is, no really, this is too simple. A $45 replacement part as opposed to a $500 replacement part.

TIA Gang. All advice welcomed.

Jim
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Old 10-04-2011, 05:45 PM   #4
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I really like those kind of fixes. But if you feel that it was to cheap of a fix you can just send me a "C" note.

I WOULD MUCH RATHER BE LUCKY THEN GOOD
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Old 10-04-2011, 06:11 PM   #5
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Quote:
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I really like those kind of fixes. But if you feel that it was to cheap of a fix you can just send me a "C" note......
Which I surely owe you for all of the advice over the years.

Replacement part should be here in a day or two. I plan to do an extended test over the weekend and see if this actually works. I'll keep you guys informed.

Jim
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Old 10-04-2011, 06:26 PM   #6
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Jim,
A thermistor is a temperature sensitive resistor. As the temperature changes the resistance chances. The board monitors the resistance as it changes and turns the cooling on and off to maintain the selected temperature. In this case turns the heating element or gas flame on and off.
By unplugging the thermistor as you did and it is now cooling and will continue to get colder and colder, tells us that the problem is either the thermistor or the board. The thermistor is by far the least costly to replace.
So I would go with the $45 thermistor. If it works your done. If not the board would need to be replaced.
Hope this info helps.
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Old 10-04-2011, 06:27 PM   #7
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Just got back from a cruise and decided we needed to take out the AS...however, I suddenly remembered our fridge is on the fritz just as is/was yours. So just opened the forum and spotted your posting and what did I find? You have the same problem as we do. I did pull out the entire thermostat and left the fridge running. Result: freezer works but lower fridge not cooling above the same 50 degrees.

Q: Does the thermistor include the entire thermostat and dial unit? (long wire clamped at the back of the fridge between cooling fins and ending at the thermostat dial unit)

However, yours worked when disconnected. Mine does not. We replaced the cooling unit about 7 years ago and that seemed to work for awhile. Not sure how long but do know that the last two years we haven't traveled much and both summers the fridge did not work very well unless it was really cool outside, and then not really that good.

Thinking seriously about replacing this 20 year old fridge with a new one. Yes, expensive but at least we'd be starting out knowing all parts work.
But....would like to think I could get off cheap here and fix it easily. Replacing is lots of work.

Gary
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Old 10-04-2011, 06:53 PM   #8
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Jim...By unplugging the thermistor as you did and it is now cooling and will continue to get colder and colder, tells us that the problem is either the thermistor or the board.....Hope this info helps.
I left out a few details. After running overnight (about 12 hours total), the fridge (yes, the fridge, not the freezer) cooled down to 27 degrees. So it would seem that the cooling unit is in good shape. That would seem to narrow it down to the thermister or the circuit board, as near as I can tell. I think I'm on the right track here. Thanks for the confirmation, Tiger.

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Old 10-04-2011, 06:53 PM   #9
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Q: Does the thermistor include the entire thermostat and dial unit? (long wire clamped at the back of the fridge between cooling fins and ending at the thermostat dial unit)

Gary,
Sounds like your model is an older type with a mechanical thermostat. Not the same as an electronic type with a thermistor and circuit board.

I would need more info.
When you say the freezer is freezing and the refrigerator is cold but not cold enough, is the freezer 30 degrees or 10 degrees?
Is it acting the same on electric and gas mode?
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Old 10-04-2011, 07:25 PM   #10
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Quote:
Originally Posted by GoldFever View Post
.......Q: Does the thermistor include the entire thermostat and dial unit? (long wire clamped at the back of the fridge between cooling fins and ending at the thermostat dial unit).....

However, yours worked when disconnected. Mine does not. We replaced the cooling unit about 7 years ago and that seemed to work for awhile. Not sure how long but do know that the last two years we haven't traveled much and both summers the fridge did not work very well unless it was really cool outside, and then not really that good........


Gary
I'm only familiar with my Fridge, so I don't know what the "dial unit" is that you are referring to. See Tigers post immediately above.

One point is that I had to leave my fridge on for an extended period of time with the thermister disconnected. After about 6 hours of operation in this manner, the fridge was only at about 50 degrees. That was around 11:00 last night. I tossed a coin and decided to leave it on all night. Remember my admonition about unattended "glowing objects" above (safety, safety, SAFETY!!!)? If you have the time tomorrow, you might disconnect the thermister and let it run for 10 or 12 hours and see if the fridge area cools down. Just keep an eye on it and use a remote temp sensor so that you're not opening the door all the time to check the temp.

Make sense?

Jim
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Old 10-04-2011, 07:37 PM   #11
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More info:
Freezer on gas and electric gets down to approx. 30deg.
Fridge no lower than 45 - 50 on both.
I have replaced the board once about 4 - 5 years ago, the cooling unit about 7.
Maybe does better on electric but only a small amount. Last trip up north it seemed to work okay plugged in at an RV park but when using gas it did not. Froze water in ice cube trays.
However, after a day on gas it did not work. At home on electric it no longer gets below 30ish but then the outside temps were pretty high at the time I was testing it.
Shut down the system and haven't used it since mid August. Now it is time to repair or replace. Frustration has set in and I'm anxious to be done with the problem, one way or another (read: cheap or expensive).
Thanks.
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Old 10-04-2011, 07:37 PM   #12
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Meant to add to that last post.......

The thermister is pretty easy to trace in my frdge. There is a two-wire white wire that is connected to the thermister inside the fridge area. It goes thru the back wall and hangs down the back of the fridge. That two wire "bundle" has a plug on the end that is plugged into the circuit board. I simply disconnected it from the circuit board and turned the fridge back one. Disconnect ALL power to the fridge before you do any of this--both 12v and 120 volt.

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Old 10-04-2011, 07:40 PM   #13
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Also: old unit (1992 vintage) is a Dometic RM3604, no longer made.
Replacement recommended by Dometic: RM2620. Fits into cabinet perfectly.
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Old 10-09-2011, 05:34 PM   #14
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Ye olde Busted Fridge, Part 2

Or, "I knew it was too good to be true". Replaced the thermister Friday night and let 'er run overnight and a good part of the day Saturday. Never got below 49 degrees, which was early Saturday morning. As the day went on, the temp slowly rose to 65 degrees. So we're back to square one. Anybody know how to troubleshoot the circuit board? I'll start sifting thru old threads.

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