Sunday, September 20, 2015

How To Fix Fridge Freezing Problem On Dometic Refrigerator

The Swedish made Dometic refrigerator is made for RV use, where it can be run from electricity or propane. Overall, it's well designed, but for whatever reason it provides no temperature adjustment. It relies on its thermistor being perfect, within a very tight tolerance.

But we all know how that works out, right? The world is never ideal, and two random thermistors off the production line might run their fridges at different temperatures. And certainly the characteristics change slightly over time. That's why almost every refrigerator on earth adds a simple variable resister to provide control.

The Problem


My Dometic 2652 Two Way fridge works, but the fridge gets too cold. Like, in the 20s. I found the service manual to this fridge, and it has a troubleshooting portion that specifically mentions this issue as either a problem with the resistor or the control board. Searching the Google machine yields others saying the same thing.



Testing


If your fridge is having the same problem, there's almost no reason to do the test, because the aftermarket kit on eBay offers the adjustment you want either way. But if money is an issue, you can test the existing thermistor.

I cut mine off to test it, figuring I could just splice it back on if it worked. But you don't have to cut it off.

The original thermistor, snipped off


The official test involves putting it in a glass of icewater and measuring the resistance. So what you can do is unclip it, and put in a glass of ice water inside the fridge. And then disconnect the 120V and the 12V systems, pull the connector, and measure the resistance straight from the connector.

In a glass of icewater, the thermistor should read 10k ohms on a multimeter. When the control board reads 10k ohms, it figures the fridge is the right temperature and turns the motor off. So if yours reads lower, then you have solved your problem.

If your thermistor has the correct reading, then it has to be the control board. I read somewhere that the relay goes bad on the control board.

My thermistor measured 5 ohms in a glass of icewater! Which means it would never tell the fridge to stop cooling, and the fridge is happy to comply. Just as an aside, I think you cold probably intentionally turn the fridge into a freezer if you so desired.

Above, you can see that I circled the connector where the thermistor connects to the controller board

Aftermarket Thermistor Kit

There is an aftermarket kit from a web site and seller on eBay that's not too hard to find with a search. I've even seen youtube videos of these aftermarket kits being used. I noticed it was a dollar cheaper direct from their web site and they take PayPal which allows you to file a claim if you don't get your order.

I assume the kit is just a thermistor and variable resister in a series, but I'm no electronics genius, and I also need a fridge very badly.

So, I ordered the kit. I thought "aww jeez, it's going to take forever, isn't it?" but I received it about a week after I ordered it, so it must ship from inside the USA.




Replacing The Thermistor

Their web site provides good instructions. I'll be honest here. I left the power connected when I snipped the original thermistor off, and left it connected when I put the new one on. My thought was that there isn't much DC current going through that thermistor, and I guessed that a brief 0 ohms reading wouldn't fry the control board. But everyone else says disconnect both 120V and 12V systems first, so you should do that.

You'll want to strip the wires to maybe 3/8 inch. Make sure to twist the ends tight, so they go right into the barrel nuts. The new thermistor has a sticky backing, and it's really sticky. You're supposed to make the area clean and dry before you stick it, but my fridge had been off for a few weeks, so it was already dry.

I mounted it upside down because I didn't have my glasses on. I realized my mistake an instant later, but the backing is so sticky, I almost hurt my hand when it finally broke free. I mounted it correctly a little farther away from the fins, figuring I'd rather have it closer to where I can see it, and the adjustment can always compensate from it not being in the recommended place. Also, I notice in the videos and photos of others doing it, that nobody else is mounting it that close to the fins, either.







Testing The Fix


I always say, if you didn't test it, then it doesn't work. I bought a little thermometer that hangs in the fridge and has a little red band showing when the fridge is in the ideal temperature range. Unlike a freezer, a fridge has a very narrow band where it's useful. Too warm, and everything you cook will make your family sick, and too cold, like mine was, and your salad is frozen. Not good.

The adjustment seems to be working so far. The aftermarket kits fixes a glaring design flaw in this Dometic refrigerator. Someday I may solder the connections and put heat shrink tubing. The barrel nuts look a little "ghetto" but don't affect the functionality of the unit.



Final Thoughts


These fridges have a reputation for being quirky, so having an adjustable temperature takes away one of its quirks. But if you wanted to keep the fridge factory original, then you could always get the original thermistor from Amazon, ebay--lots of places.

Notes:



  • RV refrigerators that can operate off of propane are much different from the ones you are used to seeing in your kitchen. They take longer to get cold, so changing the temperature dial could take several hours to reflect the new setting.



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