Swapping a 3.kw lg libero indoor pcb to turn it into a 2.1kw capacity indoor

[back2space]

Afternoon all,


I wondered if it would be possible to make a 3.5kw LG Libero unit into a 2.1kw unit by swapping the indoor pcb's over? Dimensions wise they are the same even the rows of coils appear to be the same according to the data book but are the fan motors the same size or is it all down to software that gives the unit it's duty?


One of the things that has been suggested is that the downstairs units are overkill as the rooms are not big enough. So we are getting short cycling on cooling in summer. He thinks them being changed for 2.1kw which are the same as the units upstairs (same size rooms as downstairs) would resolve the issues... He did state that it might be a complete change of the units or just a pcb change? Your thoughts greatly appreciated.

Kind regards
Richard.

[marc5180]

Normally there are dip switches on the indoor PCB to set the capacity of the indoor units. Have you checked wether this is possible on your unit?

[back2space]

No dip swithes from what I can see.

[marc5180]

No dip swithes from what I can see.

Why not download the service manual and check out the specifications on the airflow and fan motor to see if it's the same. If it is then swap PCBs.

[back2space]

The air flow rates are lower in the smaller capacity unit... This is all I think that gives if a lower duty. Lower air flow. This would be cheaper than swapping out the indoor units.

[marc5180]

The lower airflow could be caused by either a smaller fan or a PCB off a smaller capacity indoor unit.
Do you not have the specifications for both indoor units like below to compare?

See attached image.

[install monkey]

question- who determined that theyre short cycling, maybe as mark says, run it in low fan speed, maybe partially block off the filter, increase room setpoint, leave door open-cheaper than messing about, any dip switches on the outdoor to limit max comp frequency?

Afternoon all,


I wondered if it would be possible to make a 3.5kw LG Libero unit into a 2.1kw unit by swapping the indoor pcb's over? Dimensions wise they are the same even the rows of coils appear to be the same according to the data book but are the fan motors the same size or is it all down to software that gives the unit it's duty?


One of the things that has been suggested is that the downstairs units are overkill as the rooms are not big enough. So we are getting short cycling on cooling in summer. He thinks them being changed for 2.1kw which are the same as the units upstairs (same size rooms as downstairs) would resolve the issues... He did state that it might be a complete change of the units or just a pcb change? Your thoughts greatly appreciated.

Kind regards
Richard.

[back2space]

The lower airflow could be caused by either a smaller fan or a PCB off a smaller capacity indoor unit.
Do you not have the specifications for both indoor units like below to compare?

See attached image.

I couldn't find the information from the data books online.

The model numbers are: Libero E12SQ NB0 (3.5kw unit) and E07SQ NB0 (2.1kw unit)

Would be greatfull if you had this info to hand as I have tried to find it but unable to in the lg website and technical sites.

[back2space]

They already run in low fan speed and short cycle, 2 mins on cooling then 5 mins off, all internal doors are open already. No dip switches on the outdoor to limit that.

Was told that blocking the filter could cause issues with liquid return to the outdoor unit?

question- who determined that theyre short cycling, maybe as mark says, run it in low fan speed, maybe partially block off the filter, increase room setpoint, leave door open-cheaper than messing about, any dip switches on the outdoor to limit max comp frequency?

[install monkey]

is gas charge correct? - if indoor coil temp drops to 0 deg then it will stop on freeeze protection for 5 mins

[marc5180]

Blocking the filter would reduce the surface area of the coil and in theory could cause liquid flood back to the compressor but the electronic expansion valve is supposed to control superheat across the coil to stop this.

I've looked for a service manual for these units but unfortunately I don't have one and can't find one online.
I've found the specs for the airflow and the lower capacity unit does indeed have lower air flow rates (L/M/H)
I'd try and speak to LG to see if the fan motor on the smaller unit has the same fan model as yours.
If it does then swap PCB's.

[back2space]

is gas charge correct? - if indoor coil temp drops to 0 deg then it will stop on freeeze protection for 5 mins

Gas charge is fine. The upstairs units run with no problems at all. When I run these on sleep mode which puts the fan speed into ultra low for a set number of hours then no issues as airflow is about the same as the 2.1kw then. However sleep mode isn't practical as the set point is increased every half an hour for several hours so means keep having to adjust the temp at the controller. It's a shame ultra low fan speed cannot be selected permanently.

[back2space]

Blocking the filter would reduce the surface area of the coil and in theory could cause liquid flood back to the compressor but the electronic expansion valve is supposed to control superheat across the coil to stop this.

I've looked for a service manual for these units but unfortunately I don't have one and can't find one online.
I've found the specs for the airflow and the lower capacity unit does indeed have lower air flow rates (L/M/H)
I'd try and speak to LG to see if the fan motor on the smaller unit has the same fan model as yours.
If it does then swap PCB's.

I've emailed LG to ask that question I bet they would rather sell me a new unit than a pcb so prob will say the units are different.

[marc5180]

I wouldn't tell them what you intend to do because they probably will try and sell you a new unit.
Just ask about the fan motor and they'll be none the wiser.

[install monkey]

swap your upstairs pcb with your downstairs- see how it performs before you order a new pcb

[back2space]

swap your upstairs pcb with your downstairs- see how it performs before you order a new pcb

yeah I will I hope the fan motors are the same?

[back2space]

LG's response this morning:

"Dear Richard,

Even though the equipment may seem the same; the electronics expansion valve is different and will not be compatible."

No idea why they said that about the eev it's in the outdoor unit and is the same valve whatever size indoor unit is used.

[marc5180]

LG's response this morning:

"Dear Richard,

Even though the equipment may seem the same; the electronics expansion valve is different and will not be compatible."

No idea why they said that about the eev it's in the outdoor unit and is the same valve whatever size indoor unit is used.

That pretty much sums up LG.

Maybe ask them for the service manual instead. At least that way you will see it in black and white.

[marc5180]

Just found out the indoor fan motors are the same so swapping the indoor PCB will derate the indoor.

[back2space]

Thank you I have since found out the main pcb's are the same and it is the sub pcb that decides the duty.

Gonna ordee see two anyway I think this will resolve my issues. They are £37 then vat on top I wonder if I could get them from elsewhere cheaper?

[Slim R410a]

Instead of blocking the surface area of the coil, why not try some additional filter media cut to size placed on top of your filters?

This will increase the resistance/pressure drop of the fan = lower airflow.

[back2space]

Just need some final advice before I go ahead and order these.

Ive run a heat load calculation for the downstairs rooms and these are my results:

Lounge- 5.21 x 3.32 x 2.74m = 3.1kw (usual tv and 2 occupants maximum no south facing windows good level of insulation.

Kitchen- 4.24 x 4.20 x 2.74 = 3.2kw (usual appliances and a wall mounted tv maximum 2 occupants usually.

Currently installed is a 3.5kw unit ran in both rooms run on low fan speed but still cycles off quite quickly or is very drafty even on low fan speed. The bedroom is the same dimensions as the lounge and situated directly above and the 2.1kw unit copes just fine on low fan speed also. The air flow is much less forceful also and pleasant because the unit doesn't cycle so often it brings the humidity down more within the room which is what we are struggling with downstairs amongst the cycling.

The calculator I used was just one I found online do you think the calculations are correct they seem over cautious? Do you think a 2.1kw unit will service these rooms downstairs ok based on the size and information I have given. I would rather the system run for longer maintaining set point than cycle off.

Regards
Richard.

[back2space]

Instead of blocking the surface area of the coil, why not try some additional filter media cut to size placed on top of your filters?

This will increase the resistance/pressure drop of the fan = lower airflow.

I guess this is an option but won't this increase noise from the fan. My experience of wall mounts is they don't perform well with a clogged filter.

[Slim R410a]

May increase noise slightly yes but would be a nice cheap try it and see option.
No filters would be clogged if you kept on top of them.

Re your lounge and kitchen with no south facing windows I would take 1kw off each of those results - as you said it is probably way over cautious.

[back2space]

Well I guess putting filter media on is the same as putting it onto sleep mode where the fan goes into super low mode, for 1 hour. This speed matches the same as the bedroom units on low speed. We have no issues then and the units happily tick away.

So do you think I need a 2.1kw unit or a 2.6kw unit? Not sure which to get to be on the safe side. Obviously bedroom has very low heat compared to living areas. Is dropping 1kw really gonna be enough?

[Slim R410a]

Can anyone else comment on my idea of adding the filter media?
This isn't something I have done it was just a suggestion.

[back2space]

Not sure what the heat load calculators base the outside temperature on but my indoor temp is usually 21/22c.

I've heard that most systems are oversized much of the year. I currently leave windows on the catches even upstairs to let air circulate and there is no problem maintaining indoor temperature.

Don't want to to getting the 2.1kw pcb when I might need the 2.6kw pcb? I'm not sure?

[marc5180]

Can anyone else comment on my idea of adding the filter media?
This isn't something I have done it was just a suggestion.

Thinking about it a bit more....if he were to add a thicker filter media then this would act as a lack of capacity across the evaporator due to low air flow. The velocity of the molecules of air that cross the evaporator are reduced. At the same time the temp of the cooling surface is reduced since the refrigerant evaporation temperature is lower.
Since it's velocity is lower, the air remains in contact with the colder cooling surface for a longer time.

If there's a lack of air flow the deltaT for the air will be abnormally large and may knock the units off on frost prevention.

Consequently the air is cooled a lot more and it's temperature at the evaporator falls.

[back2space]

I'm happy to pay to fit the pcb's to lower the duty just want to get it right.

I guess 2.1kw only suitable for bedrooms and therefore I should maybe go for the 2.6kw what do you think based on measurements above. Given that a 2.1kw unit is already working ok in a bedroom of the same size of the lounge could I get away with it?

[marc5180]

I'm happy to pay to fit the pcb's to lower the duty just want to get it right.

I guess 2.1kw only suitable for bedrooms and therefore I should maybe go for the 2.6kw what do you think based on measurements above. Given that a 2.1kw unit is already working ok in a bedroom of the same size of the lounge could I get away with it?

For the lounge which works out at 17.292 m2 I'd say you'd be looking around 2.6-2.8kw
And for the kitchen 17.808m2 I'd say the same 2.6-2.8kw.

Personally I wouldn't de rate it to a 2.1kw. The last thing you want is an undersized unit and by my calcs if you did then you would have.

[back2space]

For the lounge which works out at 17.292 m2 I'd say you'd be looking around 2.6-2.8kw
And for the kitchen 17.808m2 I'd say the same 2.6-2.8kw.

Personally I wouldn't de rate it to a 2.1kw. The last thing you want is an undersized unit and by my calcs if you did then you would have.

I've got audio equipment in the lounge. The kitchen is a little bit longer than the lounge but the lounge is wider so about the same. I think the 2.1kw whilst perfect for the bedroom we do need that little extra duty down stairs I guess.

The duty ratings are these at done at high fan speed?

[marc5180]

Yes these will normally be taken at high fan speed.

[back2space]

Ok so what do you expect the duty drops off by in med/low fan speed?

[marc5180]

Ok so what do you expect the duty drops off by in med/low fan speed?

I dont know but if you have the airflow rates then it could probably be worked out by one of our boffins.

[back2space]

Surely when the air flow is faster u have a higher air off temp but more air flow so when it's on low fan speed you have less air flow but a lower air off temp delivering the same cooling?

[r.bartlett]

For the lounge which works out at 17.292 m2 I'd say you'd be looking around 2.6-2.8kw
And for the kitchen 17.808m2 I'd say the same 2.6-2.8kw.

Personally I wouldn't de rate it to a 2.1kw. The last thing you want is an undersized unit and by my calcs if you did then you would have.

I would say for a domestic these ratings are too high.

I would go for 100 w/m2 max so 2.1kw is ample for both.

[back2space]

I would say for a domestic these ratings are too high.

I would go for 100 w/m2 max so 2.1kw is ample for both.

Hi thank you for your reply.

Could you explain as to why you have come up with those ratings? Surely if they are ran in lower fan speed then it will pretty much match that output plus less noise of having the fan on full speed?

[marc5180]

The best thing to do would be to swap the indoor sub PCB with the 2.1kw unit from the bedroom and see if it maintains temperature.

[back2space]

I am thinking to get the 2.6kw ones rather than the 2.1kw. The airflow from the bedroom ones is quite low on low fan speed and sometimes do need bumping up so I don't want to have to be doing the same on the downstairs ones when having people for meals or entertaining guests. Low is the way so I think 2.6kw will be enough.

[back2space]

Ive attached the combination tables you can see the 7000btu & the 9000btu can both ramp down to the same output 1.8kw in cooling and 2.2kw in heating with just one unit operating. So the 9000btu unit should cover all aspects without the risk of being undersized. Just confused as to why the other person who commented on this post said to go for the 2.1kw units being in a domestic situation.

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[install monkey]

fyi mitsi heavy splits you can set the static duct pressure- set a 5 kw ducted to under 30 decibels on low speed- (general office chat is 42 decibel)not promoting them but was impressed with the fact u can press the diamond button on the remote and crank it up or wind it down

[back2space]

Not practical in this case as keeping this system just changing pcb's to lower duty. Units are only a year or so old.

[frank]

I'm a little concerned why the units are able to achieve temperature setpoint in 2 minutes then cycle back on after 5 minutes?.
Will the unit cycle for more than 2 minutes if you keep hold of the sensor?
Don't forget that the outdoor unit will also have a capacity setting and if you mismatch the indoor - outdoor capacities you may get an error.

[back2space]

I've prob exaggerated the on off times but they are short it's prob more like 5 mins on 10 mins off.

The outdoor is matched to the indoor as per the combination table. The units are just oversized.

[back2space]

I would say for a domestic these ratings are too high.

I would go for 100 w/m2 max so 2.1kw is ample for both.

Can you please explain your answer please. I don't think 2.1kw would be enough for heating?

[back2space]

Got the 2.6kw connected up and working as expected. They are about the size of a £1 coin! Question though, as per the data books with a 9000 btu unit in operation on the outdoor fm25ah ue1 the lowest it can ramp down to is about 880w input. I've got a set point of 18c which means the unit will cut off once it gets to 22c (4c differential) the room temp has been hovering at 21.5c for approx 15mins but the compressor is still drawing 1150watts whilst getting upto temp it was drawing about 1200w so it's hardly ramping down and has plenty of time to do so. Outdoor ambient is 10c. Seems to be running at rated input when it should really be ramping right down. Instead it prefers to actually go thermostat off then we have the room temp fluctuating till it comes back on.


Is it possible the sensors in the outdoor unit require replacing?

[back2space]

Hey everyone. Hope your all enjoying the sunshine and I'm sure it's keeping you busy. Just an update...

The 9000btu's are still too much capacity, units still cycling off and too much air movement even on lowest speed this is even if we close the left to right louvres so it's practically blowing sideways down the room so I am going to try the 7000btu pcb's...