LG fridge compressor not starting

[unimatrix93]

Hello everyone, my old but loved LG GR-642 stopped cooling and frosting all together.
The display shows everything as normal, the focused cooling activated when I open the doors but the compressor wont start.

First I measured the terminals on the compressor at the back of the fridge. 0 volts.
Now I disconnected the compressor and measured resistance on its leads: around 8 ohms.

I dissassembled the main powerboard, couldn't find anything suspicious but I noticed that the comps relay wont send voltage to the pin, while Fan H and fan L is indeed at 230V.

I removed the relay from the circuit and measured the correct resistance on its coils and I could turn it on with my lab psu.

What could cause this problem guys?
Thank you!

[Aliencomputres]

check the protection relay on the motor first.

[stj]

looking at con5 i think you need to clean and inspect all the connectors!

[CapLeaker]

What stj said. There should be some sort of a protection device on the compressor. Also check the compressors winding isn’t shorted to the compressor case (isolation test).
Only because a relay goes click, doesn’t mean it can handle a load.

[mon2]

What about the compressor capacitor?

https://www.amazon.ca/EAE32501017-Re.../dp/B09Z2S6NWJ

[R_J]

Does the compressor start if you press the TEST button? If you are not getting any voltage to the compressor, it is likely the comp relay is not being turned on, or the contacts are bad.
I suspect the motor fan does not spin as well as it is connected across the compressor terminals

[redwire]

Does the compressor relay activate (click)? The contacts wear out. The PTC motor starter is always a problem and might be why the fan is slow, if the relay is working clicking and has good contacts.

If the fridge is accidentally put in "demo" or "display" or "showroom" mode it will play dead as far as the compressor. It won't turn on but will look fine. My buddy had a repair guy swap the board, then it happened again months later and it turned out his girlfriend kept pushing the button sequence by accident when she was trying to change the fridge temperature!
https://www.lg.com/us/support/help-l...-1337637756594

Service manual maybe?
https://www.manualslib.com/manual/69...Gr-642apa.html
https://elektrotanya.com/lg_gr642qvp.rar/download.html

[CapLeaker]

My buddy had a repair guy swap the board, then it happened again months later and it turned out his girlfriend kept pushing the button sequence by accident when she was trying to change the fridge temperature

I started laughing at this. Something similar happened to me on a Shelly plus one and that accidental sequence erased all the programming and had to start from scratch. All I did was flicking the light switch on and off exactly 7 times. LOL

[unimatrix93]

Thank you all for your inputs.

I dissassembled the motor PTC and the overload relay.
The overlay relay seems to be okay, but the PTC shows 45ohm resistance on room temperature.

[unimatrix93]

Here is some more tests:
i connected my DMM to the comp pin.
I noticed that as I plug in the fridge, the relay clicks, the voltage goes up then the relay clicks again and the voltage drops off to 0V. It happening in 2 seconds at max.

[redwire]

You have to narrow it down - is it the control board or compressor motor?

The start capacitor is switched in by PTC Starter. Rated 47Ω 240V or 6.8Ω for 115V mains. It takes a few minutes to cool down if it was hot. So your reading is good.

Is there power to the compressor? Fan is running?
Is the control board switching on power to the compressor? Relay clicks?

The compressor motor has these to check:
Overload Protector OLP is a thermal switch
Run capacitor
Start capacitor

If the motor does not start it will overheat and trip the thermal overload protector.

[unimatrix93]

You have to narrow it down - is it the control board or compressor motor?

The start capacitor is switched in by PTC Starter. Rated 47Ω 240V or 6.8Ω for 115V mains. It takes a few minutes to cool down if it was hot. So your reading is good.

Is there power to the compressor? Fan is running?
Is the control board switching on power to the compressor? Relay clicks?

The compressor motor has these to check:
Overload Protector OLP is a thermal switch
Run capacitor
Start capacitor

If the motor does not start it will overheat and trip the thermal overload protector.

No, the compressor gets power for a second or two, then the relay turns off.
The other two pins, FAN H and Fan L getting power. Altough one of them getting 290V while the other 230, don't know if it matters.
As I mentioned, the relay does click when I plug in the fridge, delivering power to the compressor but it clicks again as it tursn of moments later.

I checked the PTC, the reading were 45ohm on room temperature, it should be okay since it's a 240V system here. Should I check If the resistance increases as I manually heat it?
I also checked the OLP next to it, which showed less then 1ohm resistance between the two pins, I guess that also good.
I couldn't find any capacitors next to the compressor so I guess it doesn't have any.
I also checked the compressor 3 pin, the values does add up correctly so I guess thats also good.

Is it possible that the relay on the mainboard is faulty?
I mean I removed it from the circuit, applied 12v to it's coils and it does clicks. But maybe it cannot handle the load anymore because of worn out internals?

[CapLeaker]

Is it possible that the relay on the mainboard is faulty?
I mean I removed it from the circuit, applied 12v to it's coils and it does clicks. But maybe it cannot handle the load anymore because of worn out internals?

Thats what I said before… a clicking relay only means the relay coil is good. Check everything redwire mentioned.

[unimatrix93]

Thank you for your help and patience everyone.
So I ordered new relays, I tought its better to replace all.

After replacing the relays the fridge compresser started right up and started cooling down both the freezer and the refrigator.
This happened last night.

Now this morning I noticed that the display showing this error code:

The display does not respond to any presses, nor opening the doors.
Altough the compressor turns on after opening the doors to cool it down.

I noticed that there is an error code list on the back of the fridge. But the funny thing is that none of the listed codes are like that on the display.

What else should I check?

[Hondaman]

I'm sorry, but here in the USA, LG is selling refrigerators with terrible "linear compressors". These compressors have rubber coating some of the moving parts. They fail quickly because the rubber is not compatible with the oil used with the refrigerant inside the sealed system. LG is not making any effort to design a different compressor. How old is this refrigerator? Can you spend the money for a different brand? I hate to give you bad news, but after you fix the electrical problem, the compressor might fail.

[unimatrix93]

I'm sorry, but here in the USA, LG is selling refrigerators with terrible "linear compressors". These compressors have rubber coating some of the moving parts. They fail quickly because the rubber is not compatible with the oil used with the refrigerant inside the sealed system. LG is not making any effort to design a different compressor. How old is this refrigerator? Can you spend the money for a different brand? I hate to give you bad news, but after you fix the electrical problem, the compressor might fail.

This unit is around 25 years old and it served perfectly for it's lifetime. We love this fridge and altough I looked around for a new unit in a case of impossible repair, but those that have similiar attributes are incredible expensive. Even on the aesthetics are perfect for my kitchen. All of the current fridge are industrial looking, plain steel or black colored. At least here in Europe I cannot find anything that even similiar and doesn't cost €1000+.
I really want to repair this fridge if it's possible.

Here is a photo of the compressor:

[harp]

But the funny thing is that none of the listed codes are like that on the display..................... it is self-test no 5, defrost error

[CapLeaker]

I see 4 leds on. Cording to the chart on the back of the fridge you got a defrost error, the fifth on that list. Check what is sez: Defrost heater temperature fuse open.

[redwire]

Yes a new problem, not related to the original problem? It looks like now if failed doing a defrost cycle.
Check all connectors, and the new relays one might be wrong.

[sam_sam_sam]

Check the defrost sensor ohm reading is it correct for the part number if has on I personally seen too many temperature sensors fail in some weird way so please check it