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defrost failure samsung model RS2555SL


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10 replies to this topic

#1 bajadean

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Posted 19 April 2011 - 02:14 AM

defrost samsung model RS2555SL with problems
freezer works great, fridge freezes up to a solid chunk of ice, and have to turn off and let it defrost for a few days, have to do this once a month.

I can put it into manual defrost and it does work and turn itself off when it hits about 60 degrees and thermistor has proper resistance readings at 18k ohms (frozen) it allows manual defrost, then around 6.3 k ohms (approx room temp)it shuts off the manual defrost power while still beeping on the defrost cycle..

because the manual defrost works and shuts off it shows all driver chips,fuses and relays are ok, is the only other thing it can be the timer board chip firmware? Or is there another input that i have overlooked.

Is there a trick/backdoor to re-initialize this chip? TMP87CC40N by toshiba.

I notice the low power reset is a fairchild KA7533 and that samsung did not follow suggested guidelines of a pull up resistor on the output to the reset on the toshiba chip. this low power notification chip stops the main chip when power drops to critical levels from losing execution steps (we call that la-la land). Maybe the chip is going into consistent la-la land (not likely to be consistent) with voltage fluctuations (this fridge is in Mexico) I do not own any type of data logger to watch this voltage over a fewdays or a few hours. Any feedback on this would be appreciated.

fan kicks on when so not that either.

this product worked fine for 3 years.

as a backdoor patch/band-aid, I am thinking of putting in a resistor in series with the defrost sensor to shift the time on the defrost cycle to be longer since it could be that it just does not stay on long enough could be a cheat. I will probably try 2k ohms to start. By the samsung appendix I chart, this would shift from 66 degrees to 85 degrees when it shuts off assuming the auto defrost uses the same threshold as the manual threshold maybe clearing the remaining ice to solve the issue.


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#2 bajadean

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Posted 19 April 2011 - 02:06 PM

I put a 2.2k ohm resister in series as I said I was going to do. It now has an error code on fridge start up of 3, so this defrost coil temperature sensor is probably calibrated to the regular fridge one.

But it worked as I anticipated when I did the manual defrost. It certainly allowed the heater to stay on much longer heating the entire mechanism to a much higher temperature, i hope enough to melt the ice. I did notice before the cold side of the coil did not really get very warm on the manual defrost. Right now they do.

I will do some more testing, maybe a 1k ohm resister would suffice. if one had 5 of these refrigerators with the same problem it might be easy to determine a good value.

the tradeoff is by having it heat up too much it could overheat the heater element or the thermal fuse. so the lowest resistor possible is the best one.

I had to use a surface mount resistor as that is all i have on hand. soldering those to a wire is not exactly easy. so till i make it to the bigger town will not be able to try the 1k resistor.

#3 bajadean

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Posted 24 April 2011 - 11:53 PM

I am testing with the 2.2k ohm resistor modification. this will take about a month to to two months determine if my modifications worked. I also put a piece of aluminum flashing on the lower part to heat the drain hole.

as of now all is working even though I have the error code of 3 on start-up. this is a slow process to determine if it is working.

as a side note, i own a second samsung with the exact same problem of freezing up solid, I will start the same process in a few days when I have time. I need to see if all resistences are correct first.

#4 Samurai Appliance Repair Man

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Posted 25 April 2011 - 07:35 AM

You probably just need to replace the thermistor, not an uncommon problem in these beasts...

http://www.repaircli...Number=RS2555SL

#5 MR. ED

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Posted 25 April 2011 - 10:31 AM

Don't stop him now he is having way too much fun

#6 bajadean

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Posted 30 May 2011 - 06:37 PM

You probably just need to replace the thermistor, not an uncommon problem in these beasts...

http://www.repaircli...Number=RS2555SL

thanks,but I did not get the error code on start/boot up of the fridge. (only after I put the resistor in series shifting the defrost curve to about 90 degrees vs the norn 60 degrees) and the thermistor resistance was correct for the entire testing range to +/- 0.5 degrees from the samsung thermistor chart in the service manual.

yet I could tell the lower side of the entire coil system was not hot enough to melt any ice that may form at the bottom. It did heat up on the manual defrost mode, so things are working at these ends. . and it did shut down at the proper temperature right at the thermistor when I was testing in manual mode. so everything was working just ice was forming. thus defect in design appears to be the issue. so did the work around and it appears to be working.

so to sum it up: My fridge would be consistantly a block of solid ice in 3-4 weeks, thus fridge was about 60 degrees on upper shelves cooler on lower. Worked fine for 2-3 years that I have owned it, and the last year has been a nightmare..

Now after 5-6 weeks I have not had a freeze up of the fridge side so far, it should have happened by now. this is after two modifications at the same time, I put in the 2.2 k ohm resistor in series to the defrost thermistor and i made a heat sink from the heat coils to the drain. I will post pictures after 2-3 months if it still does not freeze up.

samsung should have had a backdoor in their firmware to increase the time or temp to shut off in defrost mode, similar they have for incorrect temperature settings. (my fridge is to the t correct in the door vs inside) One thing I could try is they do allow a temperature shift override, but it is not for the defrost thermistor, it is for the other fridge thermistor. so one could in theory drop this temp and then set the fridge to a higher temperature. But I used a 2.2k resistor that has a much greater effect than can be achieved with a moderate shift. I did not determine how much I needed to shift the chart, this would take months of testing.





so right now I am a happy camper with my mods. and again I will return after a few months to update with pictures if still working properly.

#7 bajadean

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Posted 01 July 2011 - 06:29 PM

well I am back as prommised... great news....

well after 2.5 months I can say it is a fix indeed. I never lasted 6 weeks and the normal was 3 weeks.

so if you are giving up with all fixes because everything works like mine did but always froze up do this. do the soldering when the fridge is off. here are some pictures.

this one shows the ice left after a defrost cycle, this should not be there. It is a problem. you can see to the left it doid melt some ice, but there is still a section that is just going to keep building because it did not melt through a complete defrost cycle. I have higher resolution pictures at a link at the bottom of the post.
Posted Image

below is the 2.2 k ohm resistor in series. do it with power unplugged. just cut one yellow wire close to the connector and solder a 10 cent resistor in and tape it
Posted Image


here is a modification to the heat sink. I added some aluminum flashing to make contact on both heater bars to transfer heat to the lower part to melt the ice. make sure you have a curve contact on the bars for better contact area. not shown is I have a tapered small tab on that flashing that also goes into the drain hole to make sure the drain hole is kept from being frozen

I also added a heat sink to the left, it was not making good contact with the sheet metal, so I made a piece that made more contact and stopped it from being a hot spot. which could cause that area to burn out. they tried to do it all with the rivited points, that just is not a lot of contact area.

I bought the aluminum flashing at Ace hardware, but bet you can get small sheets at hobby shops.

Posted Image

here is a bending of the upper tabs to make better contact and allow the water to drop to the bottom during the defrost vs handing on after the defrost and freezing and adding humidity. i only did this on the top row. i did not bend the one on the left yet and you can see the water droplet right behind it.

Posted Image
here are higher resolution photos if you need them click below
fridge

#8 kdog

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Posted 01 July 2011 - 10:54 PM

Excellent Work !!!

A clear candidate for a Merit Appliantologist upgrade

Please keep us posted


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#9 Samurai Appliance Repair Man

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Posted 02 July 2011 - 07:51 AM

Agreed!

Done. Posted Image

#10 bajadean

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Posted 02 December 2011 - 12:43 PM

so my tweeks have now worked for 7-8 months. adding the heat diffusers and the resistor in series to the thermostat to change the shut off temperature of the defrost cycle. I have not had to unplug the fridge for 3 days to defrost it in all that time. when before I could not go past 3 weeks.

So by shifting the defrost cycle to be on longer my concern was I might cause the heater element to burn out. This apparently to date has not happened which makes sense since it was not defrosting it enough. If there was going to be a problem should have had a critical failure by now. But that is why I did put in the heat diffusers in place, to prevent hot spots . I now own a cheap infrared temperature reader that would have been handy to find the hotspots ($25.00 at radio shack). I did it by touch before and found these areas to be significantly hotter. They were hot...

I note this fix is for when the fridge coils freeze up and everything is working, that you know the defrost element works.. My fridge worked fine for years and would do this only once a year a couple years ago and escalated to every 3 weeks.

As a side note I bought a second one of these fridges(very cheaply) that has a similar problem, I have only added the heat diffusers to see if it will solve the problem before I add the resistors. This is up and running for a week on that fridge. that one was freezing up about every 2 months. I will report back on that one too.

#11 bajadean

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Posted 23 December 2013 - 09:56 PM

just wanted to leave an update that this fix has worked for over 2 years now.   








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