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LG Refrigerator LFCS31626S suddenly stopped cooling

lg4never

Premium Member
Joined
Jul 7, 2021
Messages
4
Location
Los Angeles, CA
Model Number
LFCS31626S
Brand
LG
Age
6-10 years
A few days ago our LG refrigerator model LFCS31626S suddenly stopped working, noticed it when taking butter out and it was soft straight out of the fridge. Luckily we still have our 16-yo $400 standard white top freezer Whirlpool in our hot garage that's still working perfectly fine. But this $2k+ LG stainless steel french door bottom freezer has given us nothing but trouble since buying it 5 ½ years ago. But before we've "only" had problems with the refrigerator fan blade getting some kind of ice buildup issue that made the fan start ticking/chopping which we had to solve by unplugging the fridge and letting it thaw out & then plug back in again, which happened like 2 or 3 times over the first 5 years.

This time was different, and we were able to find the service manual to do some quick testing to see if we could figure out what the problem was, and did some of the quick troubleshooting checks and a cleaning of the evaporator coils which while a bit dusty didn't fix anything.

Quick status of what works & doesn't:
Power is on, all interior lights and display works fine, "setting temperature" for Refrigerator and Freezer works as in you can set it to 37/0 but regardless if setting it to 33/-6 nothing happens.
Tried pushing the Ice Plus and Freezer buttons on the display for one second to see if we would get any error codes, but the display shows nothing when doing that. Releasing buttons just goes back to showing the set temperatures.
When opening up the back Main PCB panel, there are no blinking lights at all on the LED to show any of the error codes listed in the service manual.

Did "Test 1" in the service manual, where the fan in the back panel by the evaporator coils is running, and the fans in the fridge and freezer are also blowing air, but only at room temperature, not cold. Compressor is making some sounds and vibrating slightly but stays at room temperature.
Also did "Test 2" which keeps the fans on, not sure if it does anything else. Pressed the button again to do "Test 3", but it does not beep 3 times as it should, it only turns fans and compressor off which might be normal since the refrigerator is already at room temp so there's no defrosting needed. Pushing the button again turns on Test 1.

After that did tests with a multi meter on CON201 "PCB Check" disconnecting power, disconnecting the CON201 connector, powered back on and pushed the Test 1 button but only got about 40V between COM & POWER pins after the 30 seconds. Got a couple of different results testing after different amount of time after pushing Test 1. Typically 40V after 30 sec, sometimes increasing from 30-60V after changing polarity (!?), or 4.6V after more time. Not sure why that is.
According to the service manual you should get 200V on this test, otherwise "Replace Driver PCB" which I assume actually means Replace Main PCB.

Also tested voltages on CON7 and CON6 which tests the different fan motors.
CON7 pin 10 & 12 should be 8-12V, got 14.24V (which according to Service manual means replace Main PCB)
CON7 pin 8 & 12 should be not 0/5V, got 2.44V (which should mean fan is ok)
CON7 pin 4 & 6 should be 8-12V, got 11.68V (so within spec)
CON7 pin 2 & 6 should be not 0/5V, got 2.6V (which should mean fan is ok)
CON6 pin 3 & 5 should be 8-12V, got 13.18V (which according to Service manual means replace Main PCB)
CON6 pin 1 & 5 should be not 0/5V, got 2.51V (which should mean fan is ok)

So we're "hoping" the PCB is bad since that's at least "only" a $150-ish easily replaceable part and that's at least what the CON201 test and 2 out of 3 CON7 and CON6 tests suggest.

The problem is we're also concerned it could be the compressor that is bad, since the test under "Poor cooling in Fresh food section" -> Test1 -> "Windy" = Yes -> "Check the air temperature. Is it cold?" = No -> says "Check the Compressor and sealed system"
And we are of course a couple of months past the 5 year extended warranty thing from the class action suit that we just found out about yesterday, so guessing that could get expensive.

Hoping that some of you knowledgeable folks on this forum could help us out with what's the likely problem here, and if there are any other tests we could do to further narrow down what the problem is..
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,295
Location
Murray, Utah 84107, United States
Compressor is making some sounds and vibrating
Machine must be plugged in and running for a minimum 24 hours with few door openings. Leave the machine plugged in and running while you remove the evaporator cover in the freezer section and check the frost pattern on the coils. You want to see a very light coat of white frost on all the coils top to bottom. This is what you want to see:
R-frost pattern normal.jpg

You don't want to see this:

R-frost pattern leak.jpg
R-frost pattern sealed system.jpg
R-frost pattern sealed system fd.jpg


Take a few pics and post here if you like. I'll take a look. Reinstall the evaporator cover.
 

lg4never

Premium Member
Joined
Jul 7, 2021
Messages
4
Location
Los Angeles, CA
So I've had the refrigerator running now almost 48 hrs, and when opening the freezer door it's warmer inside the freezer than room temperature, measuring 81-82F with an IR Thermometer to the back of the freezer. Is there still any point opening up the back panel to check the coils, can there really be any ice in there when it's that warm inside?

Seems like with our bottom freezer we have to disassemble half the freezer to open up the back panel, so just wanted to make sure there's still a point to doing it before disassembling everything.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,295
Location
Murray, Utah 84107, United States
Is there still any point opening up the back
Nope, if the compressor is running and there's no cooling, the problem is with the sealed system. Sealed system repairs are expensive and will often exceed the machines value. Time for a new one.
 

lg4never

Premium Member
Joined
Jul 7, 2021
Messages
4
Location
Los Angeles, CA
Oh, darn... I was hoping there would still be a chance it could be the Main PCB if it's not functioning properly to operate the Compressor, guess not...
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,295
Location
Murray, Utah 84107, United States
That's basic refrigeration 101, if the compressor is running you can take all the electrical components out of the equation so you have a compressor/pump, pumping refrigerant through the condensor and evaporator and back to the compressor. No cooling means the problem is between compressor in and compressor out and that's all the sealed system.
R-Refrigerant Flow.jpg
 
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