Samsung SR-L629EVSS locked in defrost mode

[TopGeek]

I am a Brit living in Belgium. This American-style fridge-freezer problem seems to be hot weather related. It happened first last year when the hot weather arrived that I noticed both the fridge and freezer were much too warm (I have calibrated thermometers in both compartments). A local freezer repair technician changed a couple of sensors and the main control board but that achieved nothing. Then I noticed that switching off at the mains for a few minutes and back on again re-enabled the refrigeration process and the preset temperatures were reached. However, after about 4 hours, both compartments got progressively warmer again.
On the other hand, the display panel showed the preset temperatures.
I searched extensively on the Internet but got no answers so I called one of the UK experts who had posted fridge issues and he suggested using a timer to switch the fridge off and on every few hours. That worked amazingly well and stabilised both fridge and freezer temperatures. When the hot weather passed, I tried removing the timer and all was back to normal.
Unfortunately, the same thing has happened with the recent hot spell so I put the timer back. However, there is evidently a fault somewhere in need of repair.
I have seen various mentions of thermal fuses and defrost sensors but nothing precise enough to indicate if this is my problem. I have the service manual and that shows sensors and thermal fuses in both compartments but this problem affects both. For me, the fact that it works with the timer suggests that it is a problem with the defrost components but why does it affect both F and R?
If anyone has a clue, I would be immensely grateful.

[kwatt]

Re: Samsung SR-L629EVSS locked in defrost mode

Gut instinct would suggest the compressor may be cutting out as it overheats.

K.

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

Thanks for the suggestion. That was one of my thoughts but the compressor is running at 37 deg C (according to my IR thermometer). Also, if it was overheating, I don’t think it would respond to the timer restarting it.
I have been scratching my head and the latest idea I’ve had is that it could be a defective ambient temperature sensor. The service manual says that sensor causes the unit to go into defrost mode for several hours when the ambient temperature is too high. (Sounds strange but that’s what it says.) Unfortunately, they do not say where that sensor is located nor where it is connected so I can’t even check it.

[kwatt]

Re: Samsung SR-L629EVSS locked in defrost mode

Theoretically though, restarting it that way wouldn’t alter the sensor reading either.

And sensors tend to be either they work or, they don’t.

K.

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

I can’t be sure but my theory is that the timer is interrupting the defrost cycle – in effect a reset. So, whatever it is that is initiating the defrost cycle is also reset. The manual says the defrost cycle normally starts 4 hours after switch-on so I have set the timer for 3.5 hours on and 15 minutes off. That seems to stabilise both fridge and freezer temperatures perfectly. To all intents and purposes, I could leave the timer in position and everything would be fine – until the evaporators ice up I suppose. That’s why I removed it last autumn and the unit worked normally until the hot weather arrived this summer. I just need to find out what is triggering the defrost cycle and this ambient sensor seems to be high on the list.
I also assume that the electronics are designed to show the preset temperatures on the front panel during the defrost cycle to avoid panicking the owner.

[SAMURI]

Re: Samsung SR-L629EVSS locked in defrost mode

It will be a defrost system fault,
Thermal fuse or Defrost Sensor or Defrost heater.
Most likely on this model to be defrost sensor or thermal fuse.

Bob

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

Thanks but which ones? The service manual says there are defrost sensors and thermal fuses mounted on both fridge and freezer evaporators. This problem affects both.
It can’t be a defrost heater issue because the fridge and freezer temperatures rise rapidly enough to indicate that the heaters are working.

[SAMURI]

Re: Samsung SR-L629EVSS locked in defrost mode

You can only tell by testing with a meter.
Most likely the freezer section faulty.
Bob

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

SAMURI wrote:You can only tell by testing with a meter.
Most likely the freezer section faulty.
Bob

Well, it seems you are correct Bob. I dusted off my meter and fathomed out the apprpriate contacts on the Main PCB. Very fiddly work but it seems the thermal fuse in series with the freezer and drain heaters is open circuit. All other temperature sensors are functional. That means either both heaters and/or the thermal fuse in the freezer are blown. The strange thing is that there is no error code. It must also be a design flaw for that fault to cause the whole unit to go into permanent defrost mode.
Now I have the nasty task of dismantling the freezer back panels and replacing the thermal fuse – we don’t have another freezer.

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

For the benefit of anyone who has a similar experience, I have now found a video on YouTube, which confirms that a faulty thermal fuse indeed causes the initial defrost to be locked and that the temporary ‘cure’ is to switch off and on again.
The video shows how to install a new thermal fuse in the fridge compartment of a Samsung RS21 unit. In fact, the principle is exactly the same for the same type of thermal fuse mounted in the freezer compartment. The two circuits are electrically in parallel.
I have ordered a new thermal fuse and plan to do the job as soon as possible.

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

My thanks to those who responded to this topic. It is amazing how much you can learn through forums like this. I would probably never have attempted this repair without the helpful suggestions in this and other threads.
For instance, I have now learnt that the refrigerator and freezer both have identical evaporator assemblies, including identical defrost sensors, thermal fuses, heaters and drain heaters. Two separate ‘professionals’ replaced the sensors and fuses in the refrigerator compartment and seemed totally unaware of the components in the freezer compartment.
I also learnt that the defrost sensor has been upgraded and that it is necessary to replace the old white model with a new black one, even if the old one appears to be OK.

[SAMURI]

Re: Samsung SR-L629EVSS locked in defrost mode

Yes the new black sensor is more reliable and it is better to replace it at the same time.

The thermal fuse in the freezer is the most common fault and when you replace it just make sure it is not touching the heater.

Cheers
Bob

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

Thanks for the sound advice, Bob.

[TopGeek]

Re: Samsung SR-L629EVSS locked in defrost mode

Well, I made the classic mistake and ended up back at Square 1.
Probably due to my age and condition, I found it very difficult to work in the back of the freezer. There was very little frost on the evaporator and I removed that with a hair dryer. I twisted all the retaining lugs holding the heater in place but just could not get it to release. So, I removed the two retaining screws and that gave enough slack to remove and replace the thermal fuse. However, the defrost sensor (black version) was very difficult to access. It tested OK for resistance so I did not change it and re-assembled everything. On restart, it soon became evident that the thermal fuse had blown again.
The mistake I made was to not check the defrost heater and the tray heater as I can only think one of them is shorted, (they are wired in parallel and in series with the thermal fuse).
Consequently, I am back to using the timer and that seems to work perfectly. Correct and stable temperatures are achieved so I think I will continue to use it like that and forget about attempting any further repairs.

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