FIXED LMXS30746S linear compressor, dual eval not cooling

Rawmilk31

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Apr 22, 2019
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Model Number
LMXS30746S
Brand
LG
Age
1-5 years
OK Guys and gals, I was called to a new service that has me scratching my head. LMXS30746S LG 4 door fridge. It has the Linear compressor (I know junk, many repairs), with dual evap for freezer and refrigerator. it has a 3 way valve to controls the cap tubes to the evaps. My issue is the compressor is a 0-220 volt unit, looking at it it looks normal with 3 contacts. however this unit only has 2 wires, the hot and common to the compressor, the top right pin is not used. the capacitor is rated up to 450V. Question I have, when testing the fridge the compressor appears to turn on, makes vibration like normal, maybe not as much as a conventional one, but this linear style is suppose to be less noise. I evac system, removed compressor, and plugged in the compressor. It does start up and builds pressure, but with it removed i did not have a pressure gauge on it. when installed, i get no change on the high side which is connected to the dryer when turned on. I did replace the 3 way valve thinking i had a clog in the system.

Has anyone had experience with this compressor? i am trying to find someone that has experience with it to explain how it operates without the third start terminal being used. I am thinking i have a bad compressor?
 

rickgburton

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You're only giving me part of the story.
Rawmilk31 said:
...when installed I get no change on the high side....
When? After it was vacuumed and charged with the correct amount of R134a? How did you charge it, process tube, high side service valve? The low side pressure was...???? Check your gauges and hoses.
 

Rawmilk31

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Sorry let me clarify, before anything was done, tested system, compressor seem to be functioning (by feel) with minor vibrating, no codes or LED fault lamp on PCB, however High side did not get hot and low side did not get cold, (easily saying compressor was not pumping properly.) High side stayed at consistent 45psi Removed charge, (correct amount 134) removed compressor, plugged in (compressor) and tested, with just my finger over the ports it was slightly sucking and building pressure, however not as much as I would have expected. this is when i realized it only used two of the three terminals on the compressor.

I went ahead and reinstalled the compressor, pulled vacuum to ensure no leaks or moisture, charged using the charge port on the compressor, with the gauges installed, the low side charge port does not read anything and the high side port 40PSI(only one installed) it is on the high side filter dryer. hopefully that makes more sense. yes the charge of 134 was to the correct quantity. My issue is that the other repair service installed a new compressor for the customer, but couldn't get it working and said there is most likely a clog in the system somewhere. they said after calling LG, they determined in to be unrepairable. I don't buy that, I am not seeing the higher pressures if the compressor was operating. when the compressor was out i blew air threw all the lines and everything was clear.

I am thinking it was a faulty compressor. if cap tubes were plugged i should still be getting hot temps on the high side right off the compressor correct? I have read other forums where that was the case with this Linear Compressor style. (faulty new one) Customer says it was a $2500 fridge and i get irritated when I can't get something fixed. If it worked before i should be able to get t back up and running:)
 

rickgburton

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It's definitely a bad compressor. You're correct, it's not pumping. What voltage are you reading at the compressor?
 

Rawmilk31

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It's definitely a bad compressor. You're correct, it's not pumping. What voltage are you reading at the compressor?
120V, but fluctuates, I don't think my meter is fast enough to catch the higher pulses coming from the capacitor, but i do have line voltage.
 

rickgburton

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OK, you can't "bench test" a linear compressor or an inverter compressor. Connecting 120 VAC to a inverter compressor will damage it. I don't know about linear compressors. The Linear compressor is run by the inverter board whichcontrols the compressor and supplies constant voltage and constant frequency to the compressor and protects it. It works like this in three intervals; Drive half stroke after turning on initial power for 1 second. Then, Reach Target Voltage by increasing 0.35 Vrms per every 0.3 second. Once reaching the target input, input naturally changes according to refrigerator load without any special control.

Interval 1) Half stroke interval - after initial running, stay at the initial value for 1 second

Interval 2) Running interval - Increase at every 0.3 till it reaches the target input; it takes about 1 minute

Interval 3) CVCF (Constant Voltage Constant Frequency) interval - Run by target voltage and main operating frequency and the input naturally changes according to refrigerator load

This is for a linear compressor for a similar model but should be the same as yours
LG Linear.jpg
 

Rawmilk31

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Is that just Volts AC on meter, Red to Power term and Black to capacitor terminal with the wiring unplugged?
 

rickgburton

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That's correct. The Test 1 mode is push the button on the board once.
 
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Rawmilk31

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OK compressor resistance s 8.6 ohms,

Here is the trouble chart I am following in the service manual. Notice the different terminal it wants me to check. Power to the Communication term. not the capacitor term.
View attachment Compressor test.pdf

Here is a video of this test from the multi meter:
[video=youtube;4kt_GXnvRPQ]https://www.youtube.com/watch?v=4kt_GXnvRPQ[/video]
 
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rickgburton

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Looks like maybe two problems. I would say the board is bad since there's no voltage after 10 minutes (0V-120V-0V-120V = no voltage). The two different test points are actually the same since the capacitor shares a common connection with the compressor.

And going by your description, no blinking LED and compressor not working, follow the flow chart to replace compressor:
Snapshot_1.jpg
 

Rawmilk31

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That’s actually what I came up with. Possibly two issues. I have a PCB scheduled to be here and installed on Thursday, and I’ll have another compressor on hand just in case. I’ll update once repair is complete. I’m honestly thinking just PCB though. The video I posted is following the compressor test with pushing the test button. (At the very beginning).

When running for ten min, I just put the DVOM leads into the back of the term at the compressor (everything connected) and I get 130v then Ol then 130v then OL. Acts like it’s trying to get it started or longer throw for more pressure but it doesn’t have enough voltage from the PCB.
 

rickgburton

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Test the voltage when you get the new board. The board changes the frequency of the voltage, in effect changing the voltage. Less expensive meters can't compensate and are unable to read the output voltage only supply voltage.
 

Rawmilk31

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Fixed!!

Ok so it is fixed and cooling great now!! So it turned out yes the compressor was bad. PCB was functioning normally. However after installing new compressor, it still didn’t work. I ended up turning the comp on saw pressure build up to 50 psi, and hold. I opened the valve on the low side and pressure would continue to build. So that told me I had a clog and it basically had nothing to compress.

I ended up unsoldering the connections at the 3 way valve going into the Cap tubes and the previous repair guys apparently clogged the cap tubes. I cut off clogged ends, inserted approx 1/2” in and re-soldered.

Charged and found fridge did good but freezer didn’t cool. Appeared to have a clog also because evap for freezer was not cold. Ended up blowing air through and no go. Unsoldered evap for freezer and what do you know, clogged cap tube. These guys were pathetic. Fixed that. Pulled vacuum recharged and good to go now.

I will say the 3 way valve appears to be normally open and only closes when the computer see the correct temp achieved either in the fridge or freezer. My current pressures are about 15 psi Low and 105 high. When the freezer evap was plugged but fridge was working good. My pressures were -10low and 105 high. I mention this in case someone else needs this info if they are having issues. I couldn’t find anything online to help with pressures. Outside temp was 64F also.

Thanks guys of all your help.
 
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