LG multi split Fault??

[Collie]

Hi guys,
Looking for some help on an LG multi split.

Model: LG FM24AH 410A

One condenser is feeding two wall mounted indoor units that do heating or cooling and serve the same room. One unit was shutting down after about ten minutes of running and some kind of warning lamp comes up on the display. Shortly afterwards, the second unit shuts off also.

The unit that shuts down first does no cooling at all and the second unit does a little but not much. When I investigated the outdoor unit I found two compressors, one variable speed and one fixed speed. The variable speed one is the only one that seems to run for some reason. It ramps up to about 8.5 amps and cuts out like on a thermal overload as it gets quite warm. The suction pressure is good though, about 8 bar (410A).

I set the system for full cooling and it was quite hot in the room yet the constant speed compressor just will not run?? Its as if the variable speed one is trying to do the full load for both indoor units but it cant manage it and eventually fails. I can see on the diagram that a simple relay on the PCB needs to close to bring the fixed speed compressor on but it doesnt seem to be calling it although its calling for a full load of cooling.

Is anyone familiar with the sequence of operation of these units? I dont want to order a new PCB and find its something else :eek:

[Yuri B.]

Are not by chance the indoor units blowing air on each other?

[Collie]

no, definitely not. They are mounted both on the same wall about four meters between them and they are both blowing in the same direction. Its not a fundamental problem because they used to cool just fine so its something thats gone faulty.

[Yuri B.]

You can check windings of the second compressor, with an ohmmeter, to be sure the compressor is at least alive. However, I think, the system started losing gas.