LG Multisplit indoor unit stopping

[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!!

[Tayters]

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.

[back2space]

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?