LG Multisplit indoor unit stopping

Hey all,

Brief background - I've inherited an LG multisplit system with my house and experiencing the following issue;

The system is a 4 split, but with only two ways connected. (C&D) There did used to be circuits on a and b but these units were upsized and as a result the odu became too small to handle the load.

As such I have a 7kw odu, connected to a 3.5kw ducted system on circuit c and a 3.5kw wall mount on circuit d.

If I call for heat on any of the units, all is well.

If however I call for heat on both the following happens;

Both units will initially heat - the odu ramps up.
Shortly afterwards circuit d drops into a preheat state and the odu ramps back down.
Circuit d does not restart until the unit on circuit c is shut down, nor does it appear to restart once circuit c has no demand.

Is there some sort of priority setting on these units? My second thought could be a gas shortage causing the odu to cut demand to keep pressures up elsewhere in the system.

I'm not familiar with the lg multi range so wanted to ask if there was something simple I've missed before I spend £££ and call out a service tech to do whatever needs be done.

Thanks!

I had an old LG inverter system and had nothing but problems with it LG in the end decided the indoor unit were not compatible with the outdoor unit and replaced it for me. All works great now. I had similar issues.

Provide model numbers along with piping lengths and also if this occurs with the set point on the unit cutting off turned to maximum.

Where in the UK are you?

So, took me a while to get all the info...

Indoor Circuit A is an MB12AHL ~12m piping length
Indoor Circuit B is an E12SQ ~ 6m piping length
ODU is an MU4M27

Been doing a bit more troubleshooting;

When heating on circuit B - it heats, but nothing like it should do.
If however I run up circuit A to heating... the heat output from B increases dramatically - A also heats.

If I run the fan on circuit A while B is heating - I get heat from this unit as well which I wouldn't have expected.

Im beginning to wonder if the control lines for A & B are simply the wrong way round in the ODU
Im not suspecting a leak - the heat output is there, its just not provided to B unless A is running also

Confused to say the least!!

Hi Scott.

On some makes all coils will get slightly warm in heating and the ones that are actually calling for heat will get the full whack. The reason is so that no oil from the discharge ends up on a dead circuit and usually you can't run the fan in the non heating coils to save blowing hot air from that specific indoor.

To test for crossed wiring is pretty straightforward. Run one indoor in cooling and make sure the other coil doesn't cool. The same for heating applies. If you had an issue here the indoor coil would be getting scorchio and probably get a head pressure fault outside so that probably rules out that avenue.

LG's are prone to failing sensors so perhaps worth checking by resistance measurements although I suspect you have deeper issues as back2space had.

Cheers,
Andy.

Quote:

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Originally Posted by scottmcgur

So, took me a while to get all the info...

Indoor Circuit A is an MB12AHL ~12m piping length
Indoor Circuit B is an E12SQ ~ 6m piping length
ODU is an MU4M27

Been doing a bit more troubleshooting;

When heating on circuit B - it heats, but nothing like it should do.
If however I run up circuit A to heating... the heat output from B increases dramatically - A also heats.

If I run the fan on circuit A while B is heating - I get heat from this unit as well which I wouldn't have expected.

Im beginning to wonder if the control lines for A & B are simply the wrong way round in the ODU
Im not suspecting a leak - the heat output is there, its just not provided to B unless A is running also

Confused to say the least!!

---

Ok, this is exactly the same issues I had, see following post which goes into a lot of detail.

http://www.refrigeration-engineer.co...-there-I-think!

The reason all the coils get warm is that the valves remain open in heating mode 10% on units that are off or in standby. This is to allow oil to return back to the compressor. You also have the fans on units that are on standby turning on every few minutes to sample the air temp.

The issue I had is on the wall convertible units even though they were at standby the fans would continue to run all the time refrigerant was passing through them whenever the coil got above a certain temp, even though the room was up to temp. The fan would run until the coil temp dropped which was pointless and a design issue by LG. All the newer units the fans will run for 30s every 3 minutes to move air across the return sensor to sense the room temp. Because the convertibles did not have a command to keep the fans off at thermostat off this caused them to steal the heat that the outdoor unit was putting into the circuits to supply heat to one room that as still calling for heat. The outdoor unit just sees demand for one unit so ramps up/down to supply the right ammount of heat for that coil.

So the wall mount in one of my rooms would not get out of the ultra low fan speed as the coil temp was so low. The only way to get the unit to heat properly would be to turn the convertible units off or have them set at a higher temp so they were calling for heat. Verified by blocking the air intake on them so that the coil temp would not lower even with the fan running. The issues I was experiencing were the same as you.

I expect for you the unit that is stealing all the heat is the ducted unit as the fan on those tends to run constantly on low even at thermostat off due to being ducted, you can probably turn off in the wired controller then you will have sorted it (set the wired controller to read the temp from the controller). I would call LG technical and ask how to turn that off? If you have a wired controller I can prob help you through that to be fair.

Unfortunately for me the only way to resolve it was to get rid of the convertible (floor/ceiling) units as I couldn't turn off the fan logic on them. I did this when I moved house and the units heated as they should. However the act of mixing new indoor units with an older outdoor unit I then ran into a whole host of new control issues in cooling mode.

I now - still have LG, a new outdoor unit and 4 indoor wall mounts and more than happy. Does a great job of heating and cooling.

Happy to help if I can. What happens when you only physically have one unit turned on? I.e circuit b off or vice versa circuit a turned off?

I will check that when I get home today.. from memory;

A but not B - A Heats, but seems to ignore setpoints on the wall stat
B but not A - B Heats, reduced output
A + B - both run at full output

Ok yes please clarify... Unit A but not B do you mean unit B is sat waiting for the room temp to drop in standby or thermostat off.

B but not A, what is unit A doing when B is heating?

When you say the wall stat do you mean the wired controller?

There's a 4c off set in heating which you wont have been told about.. so if its reading from the wired controller it will add 4c onto the temp you set at. So 20c it will achieve 24c before cutting out. This 4C deadband can either be turned off in the controller or you will have to do the below.

If you want 20C you need to set it at 16C and it will maintain that. This is to take into account that hot air rises so floor area is going to be colder than ceiling height where the duct work is. EG 22C set it at 19C and so on.

Regarding circuit B heating at reduced output is this while circuit A is in standby mode, eg its continuing to blow warm air but has likely reached temperature, as explained in my previous post the fan is running on but in low fan speed. We need to disable this.

First need to run both units on their own, e.g unit A on its own and B turned off on the controller and vice versa, then report back.

Ok, Here are the results of that;

Unit A(Ducted) Running Setpoint 30oC - Heats as Expected
Unit B Off at wall controller

Unit B (Wall) Running Setpoint 30oC - Runs at reduced output from the start
Unit A Off at wall controller

Unit B Running SP 30oC - Full heat output
Unit A Running SP 30oC - Heats as normal

Unit A at temp - sits idle, wall controller shows preheat
Unit B - SP 30 oC - seems to be normal - going to add a few temp probes tomorrow to graph the air on and air off temps to be sure

Unit B at temp - sits idle, no fans - wall unit shows Heating & Preheat
Unit A Running SP 30oC - Heats as normal

Unit A Wall Plate Config;
Config Switches set at:
Multi / Single (Single)
Controller / Unit / Controller + Unit (Controller)
Low Pressure / Med / High (High)

Unit B Config Options:
01 (Force Run) - 00
02 (Address) - 00
04 (Thermo) - 01 (Wall Plate)
07 (Group) - 01 (Master)
09 (Dry Contact)- 00 (Off)
10 (3 min delay) - 01 (Set)
12 (oC / oF) - 00 (oC)
20 - 00 (unknown)
21 - 00 (unknown)
22 - 00 (unknown)
24 - 00 (unknown)
30 - display shows 012 where the temp is displayed

For ref Unit A controller is a PQRCUDSOS
Unit B is a PQRCUSA1

Quote:

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Originally Posted by scottmcgur

Ok, Here are the results of that;

Unit A(Ducted) Running Setpoint 30oC - Heats as Expected
Unit B Off at wall controller

Unit B (Wall) Running Setpoint 30oC - Runs at reduced output from the start
Unit A Off at wall controller

Unit B Running SP 30oC - Full heat output
Unit A Running SP 30oC - Heats as normal

Unit A at temp - sits idle, wall controller shows preheat
Unit B - SP 30 oC - seems to be normal - going to add a few temp probes tomorrow to graph the air on and air off temps to be sure

Unit B at temp - sits idle, no fans - wall unit shows Heating & Preheat
Unit A Running SP 30oC - Heats as normal

Unit A Wall Plate Config;
Config Switches set at:
Multi / Single (Single)
Controller / Unit / Controller + Unit (Controller)
Low Pressure / Med / High (High)

Unit B Config Options:
01 (Force Run) - 00
02 (Address) - 00
04 (Thermo) - 01 (Wall Plate)
07 (Group) - 01 (Master)
09 (Dry Contact)- 00 (Off)
10 (3 min delay) - 01 (Set)
12 (oC / oF) - 00 (oC)
20 - 00 (unknown)
21 - 00 (unknown)
22 - 00 (unknown)
24 - 00 (unknown)
30 - display shows 012 where the temp is displayed

For ref Unit A controller is a PQRCUDSOS
Unit B is a PQRCUSA1

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Ok so just wondering what has changed as your saying now it's working ok when either unit in idle? You said before unit A Ignored the set temperature?

Have you reduced the desired set point to match the 4c differential since you are measuring the return temp from the controller?

Out of interest what are the capacities of each unit?

Wall mounts will produce lower air flow than a ducted unit and if the wall mount is a smaller capacity unit the outdoor unit will not work as hard when only that unit is running.

Unit A seems to ignore set - if B is set to off on the wall panel... at present the set point is 16, room is measuring 24 oC and its still going.

Each unit is 3.5Kw capacity. I'm just not getting how the wall unit is throwing out much more heat when the ducted unit is not online, either as heat satisfied or calling for heat than when it is offline (off at control)

So unit A where is it reading the set point from? Is it in the ceiling void or from the controller on the wall? What if you hold the sensor with your fingers does it eventually go off?

Unit a is reading from the wall controller

You’re right - I can force it off by holding the therm probe from inside the controller

Just leaves the low output from unit b only... could it be because it has a group address of 0, so maybe circuit A instead of 01 - circuit b? Not sure if that’s how the addressing works?

It would be easier to call you on this...

Multi split are auto addressing, this setting is for group control on large systems.

So if the unit is not turning off then it looks like a faulty sensor in the controller. Where were you reading the temperature from to get 24C?

Shall I PM you a number?

The house has a 1-Wire bus system installed for ambient measurement - reading from that.
I'm not all that bothered by the overrun on Unit A, more the lack of performance on unit B unless unit A is calling for heat... B is in the coldest room!

Lets discuss this over the phone, PM me your number.

So, managed to do a bit of data collection on the wall unit; attached is a graph of operation from a cold start.

Beginning of the graph is Unit B Run Heat, Unit A off.

at 19:51 Unit A is powered up and calls for heat.

at 21:01 Unit A goes off on thermostat (standby)

at 23:06 Unit A calls for heat again

At least from that I can see that unit B does indeed perform better when A calls for heat... but Im noticing a bizarre ramp down behaviour earlier in the day which I cant work out why?!

For reference, Blue is Air On, Orange is Air Off, Grey is Ambient (sited at wall controller position), yellow is the difference between on and off air.


Attachment 15123

To me nothing stands out as abnormal when 2 units are calling for heat the outdoor unit is running faster so the air off will be a little higher hit it still fluctuates up and down as the figures show. At 17.51.01 is this a thermostat off or a defrost oil return cycle which occurs at a preset running time or if the coil is iced up.

When the system first starts it will be working harder also. No issues I don't think here.

PM me your number if you want to discuss further.

Scott

Did you sort this out or still need advice?