LG Mini Split Electrical Troubleshooting

[mpire]

Hey guys, I'm troubleshooting an error on the mini split.

Its an LAU096HV outside unit.

The inside unit was replaced last year due to a leaking evaporator coil.

Now I am getting a electronic error.

The system will run for several hours and then kick off. Its cooling, its doing its thing, but it seems to be worse the colder it is outside.

The screen says C6. That translates to:

LG AC Fault Definition = Excessive current at inverter DC power circuit – DC Peak Power

The board (6871A10135Y) says it was manufactured in 2009. The caps are all on the board. There are 3 about the size of a D cell battery. The board looks good, brand new even. Everything in the outside unit looks good, no obviously bad caps or whatever.

The only thing that looks funny to me is the thermistor on the bottom of the AC unit and its covered in green corrosion at the tip.

I can get a new board for $250.

I can get a new inverter for $60

I found a new outdoor unit for $500 on fleabay, but shipping is ridiculous.

https://www.ebay.com/itm/LG-LAU096H...386058&hash=item2cc1ce91e2:g:s-AAAOSwl-BZuaUU

I can give up and get a whole new system for $800.

I am trying to figure out how to test the inverter, so that is on the to do list.

What would you do, throw some ideas out there.

Thanks in advance.

 

[Done That]

Well, the thermistor may well be reading outdoor ambient (maybe something else, depends where it's placed) as an input to the inverter, so if it's messed up that could explain why it's getting worse with lower temps.

I'd try cleaning up the suspect thermistor, or replace it if it has a plug-on connection at the inverter. Also if you can unplug the thermistor you should be able to measure it's resistance, see if you can find a value in the unit literature etc to confirm it is in it's normal range.

Try to eliminate the easy stuff first before you spend any $$....

 

[mpire]

OK, so the thermistors look fine. It has two white wires that run from the control board under the condenser and then back. Its got a braided cover over it.

It appears to by CMFMEE31224801 called a sump heater.

I wonder if this has gone bad so it won't work when its cold out.

No idea how to test this.

 

[Jackfre]

LG should have a ladder diagram for troubleshooting. Contact the local Rep and have them get you access to that info

 

[justinjoyal]

LG should have a ladder diagram for troubleshooting. Contact the local Rep and have them get you access to that info

I’m not sure they will provide that info.

I know I wouldn’t...

 

[Done That]

Is that an external sump heater wrapped around the compressor shell? Belly band heaters like that are just a resistance element controlled by a snap disk.

Inverter compressors usually use the motor windings as a sump heater.

That said, sump heater is mostly there for off cycle protection. Once a unit is running it generates enough heat that the sump is out of the picture. Since yours runs several hours I wouldn't think that's the issue, but a inverter PCB can read bad inputs anywhere and lose its mind.

 

[mpire]

No, the heater is a long cord it looks like, but it runs along the bottom of the condenser. I assume to keep the gas mixed up? I don't really know.

Seems to run longer the hotter it gets. It was 86 yesterday and it worked fine during the day.

 

[justinjoyal]

No, the heater is a long cord it looks like, but it runs along the bottom of the condenser. I assume to keep the gas mixed up? I don't really know.

Seems to run longer the hotter it gets. It was 86 yesterday and it worked fine during the day.

What you are describing is the base pan heater. It keeps water from freezing during defrost cycles.

http://www.lgdfs.ca/en/base-pan-heaters.aspx/PQSH1200

 

[mpire]

Just to resolve this thread, I gave up and replaced the main circuit board.

The old board looks just fine, caps look good, no burn marks, etc. It worked just fine as long as the outside temperature was OVER 75 degrees. If it got below that the system would throw a C6 error. It ran fine for months and months during the day, but would error out as soon as the outside temp dropped.

I also replaced the indoor circuit board, both inside thermisters, and then all three outside thermisters. I had the inside parts from the old unit, so I didn't have to pay for those. The outside thermisters cost me $30.

I have to assume I have a hairline crack somewhere in one of the circuits that would separate when the board got cold enough and the connection separated.

The new board looks like a newer model, it has 2 large caps on it instead of 3. So maybe this is less vulnerable.

Problem solved. $220.