LFX31925ST/06 LG Refrigerator suddenly stopped cooling

javijavit

Member
Joined
Nov 24, 2019
Messages
1
Location
WI
Model Number
LFX31925ST/06
Brand
LG
Age
6-10 years
This one will be interesting. This is a large french door with bottom freezer style 30.7 cu.ft. expensive type. Suddenly stopped cooling. Worked on by a qualified certified technician recommended by LG. He identified a bad linear compressor. Compressor was replaced. After replacing compressor, the refrigerator started cooling but would not get to set-points. Refrigerator hovered around 41-45F (33F lowest and 37F middle setpoints tried). This is if you never open the doors. Freezer hovered around 3-8F (-6F and 0F setpoints). I can live with the freezer. Cannot live with the Fridge not getting to 40F. Cooling process is extremely slow. Takes over a day or more to cool down.

Tech came now a third time to work on it. This time he dismantled the whole thing, tested the evaporators and everything he could find for leaks with a spray and UV glasses. He also emptied the system and said that he collected exactly the same weight he had originally charged with so he does not think there is a leak. He recharged the system again more precisely and said there is nothing else he can do because for him it is working fine. Compressor is cooling and freezer is getting to temp. He was as puzzled as me as to why the refrigerator cannot get to temp while the freezer can.

This weekend I dismantled it again and examined the evaporators. The refrigerator evaporator (this big fridge has two, one for freezer and one for fridge) is not building much frost. Only the top first 3/4 of the first pass (strip) gets some frost. All the other sections of the evaporator are not cold to the touch and are not building frost. Also the system last nigth seemed to go into a defrost cycle because all the frost on the top was gone by the morning. The entire evaporator had not frost and some water droplets only on it. The refrigerator was at 41F at this time.

I have some sophisticated temperature dataloggers and I have been placing them inside under multiple conditions. Take a looks at the results. The last one is the one that has me most puzzled, where I placed a direct contact thermocouple to the end of the fridge evaporator coil (the section of the evaporator that appears to not be getting cold (forming frost).

This was one trial, Red is freezer, Blue is Fridge. Only opened twice where you see the two spikes. It took 12 hours to get from avg 50F to average 43F and then it sat there. I opened it around 7pm 11/14 and this time it tried to cool faster and got down to 38F, then it went back to hovering around 43F avg (+-3F). 12 hours later it decided to try to cool again and went down to 37F. Then it kept rising from there and at 5pm 11/15 it was at 45F and I had not opened the doors. Eventually you can see around 7-8pm I opened the doors and it started its slow cooling process to get to average at 43F. As shown in title, setpoints are 33F fridge and -6F freezer.
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This next trial I was going to leave t for 1 week of normal use to see what it did only opening it in the evenings for a bit when I got home from work. The first spike of the freezer that it went to 20F was at 2am. I was obviously sleeping then so I assume that it was doing a defrost cycle. Here the freezer was set to 2F and was averaging around 4F if you ignore the times it spiked up to 20F. Some of those was when I opened it shortly and some may be a defrost cycle, not sure how often a freezer does those. Here there appears to be a 20hr cycle where it spikes up. Now the freezer you can see that it can get very close to setpoint. Refrigerator (blue) on the other hand is set to 33F and only gets to 41F averaging more like 45F or higher.
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This last test was this weekend where I dismantled it again to expose the evaporator of the fridge and it just had a bit of frost over half of the top first pass. The other coil passes had no frost, they didn't even feel cold. I went ahead and placed a contact thermocouple touching the end of the last pass of the evaporator coil to see what the heck is happening and to what temperature is it getting to (red graph). Keep in mind that I did test the fans and with the doors closed, all fans work, they shut off when doors are opened. The three spikes was when I opened the doors. For this test I did not fully install the back panel, so the fridge was more exposed to the evaporator and you can see it was able to cool a little bit more (below 40F - this time the BLUE graph is the fridge not freezer, because the red was the evaporator contact temp). What is weird however, is that the refrigerator temperature is literally mimicking an odd behavior of the evaporator where precisely every two hours the evaporator goes down to below 0F and then quickly starts heating itself up to roughly 40F. I know and have read that evaporators heat themselves up to go through a defrost cycle. But if this is what this one is doing, every two hours seems ridiculous to me. DOES ANYONE HAVE ANY IDEA OF WHAT COULD BE HAPPENING WITH THIS REFRIGERATOR. I AM ABOUT TO GIVE UP!!!

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ANY HELP IS GREATLY APPRECIATED!
 

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rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
35,559
Location
Murray, Utah 84107, United States
My guess is the tech doesn't have enough experience to do sealed system repairs on dual evaporator systems. The problem you're having is with the repair. I don't know what he's doing wrong but it's definitely something. Maybe he's not putting the 3-valve in the home position.
 
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