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Samsung RFG297ACRS/XAC not cooling

dsbus

Premium Member
Joined
Mar 2, 2022
Messages
2
Location
Canada
Model Number
RFG297ACRS/XAC
Brand
Samsung
Age
More than 10 years
Hello, my 2010 Samsung fridge has stopped cooling. We first noticed that the freezer was getting warm and the fridge was still getting to its set temperature of 4degC. However after a few days the fridge temperature started creeping up as well, with the freezer at room temperature and the fridge about 5 degrees colder. Now there is no cooling at all. I had a fridge technician come in, who recommended changing both the inverter and main PCB but he did not seem confident that would fix the issue so I did some debugging.

Here are a few steps I have taken so far:
- verified all fans are working (freezer, fridge, condenser)
- I left the unit unplugged for a few days and there was no change.
- checked the compressor start relay that is plugged into it, this seems fine.
- compressor pins ohm out ok (all the same about 10ohm)
- I checked the fridge evaporator coils, at this point the fridge wasn't very cold and I saw just a bit of frost near the top.
- The inverter board has a single red LED
- I checked both boards for damage/blown caps but they look fine
- No error codes on front panel when queried
- When first plugged in the compressor starts at the high speed for about 5-10 seconds then goes to a lower speed .. I am guessing it should stay at the high speed until things cool. - After being plugged in, the compressor is always running at a low speed and occasionally (maybe once an hour?) speeds up for 5-10 seconds then slows again.
- Inverter board output to the compressor, this is hard to measure since it is PWM, but it does look like about 190VAC across the windings so I'm guessing that is correct. My multimeter measures frequency, and I see 4kHz when the unit first starts and compressor sounds like it is at high speed, then drops to 9kHz when it goes to low speed. My meter would be averaging, and I'm not sure if this compressor is voltage-controlled or frequency-controlled or both.. but I'm guessing the compressor is doing what it is told as it does change speeds when the output of the converter changes.
- 'Force freeze' mode doesn't appear to change compressor speed
- 'force defrost' mode does shut off the fans and compressor

With the fridge staying cool for a while, I thought it could be the step motor valve, but I believe this would get stuck to cool only the freezer, or get stuck in the position to cool both.. not stuck closed or stuck cooling fridge-only. So now I'm wondering if the control board is telling the inverter board to do the wrong thing. I read that the RPM signal to the inverter board is 2.5Vdc but I am guessing that is is a square wave with frequency to instruct what speed to run the compressor at? I don't see anything else that would control this speed.

So my next steps are to check the impedance of the step motor coils (not sure what these should measure but I am guessing about 10 ohm and both the same), and check that 13V is going to the step motor. I will also check the RPM signal to look for 2.5Vdc. If that's not there, I suspect the main PCB needs replacing. If it is there, I will check the frequency of that signal as well to see if it changes 5-10 seconds after I plug in which corresponds to the compressor slowing down (but maybe the unit is still booting up for those first ten seconds). I'll try to check it again when I go into FF1/2/3 mode to see if it changes. Is there anything else I should check? Is there anything that overrides the FF1 mode, that wouldn't show up as an error code?

Also anyone know how are things are not cooling if the compressor is running even at a slow speed? I'd expect a bit of cooling as long as the compressor is running even if it is running slowly. But maybe that is normal and it's in some sort of standby state, as I think the compressor is always on unless it's in a defrost mode...?
 

JEK12

Member
Joined
Apr 9, 2022
Messages
1
Location
Canada
Sounds like you have some technical expertise. My fridge did almost exactly what you described above. What was your resolution?
 

dsbus

Premium Member
Joined
Mar 2, 2022
Messages
2
Location
Canada
In the end I could not fix it. I think it was something with the closed system. Either low refrigerant, refrigerant clog, or bad compressor.
 
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