LG Multi Split MU5M40

Hi

I have a LG Multi-Split MU5M40 unit with a problem. There are five indoor units attached to the condenser. Units 1,4 & 5 seem to run fine with no issues, however unit 2 and 3 will run for an unspecified time then for no apparent reason these units will stop cooling. I have checked the indoor unit thermistors and even changed one of the units PCB boards as the LG specialist advised it could be the compressor relay on the indoor board.

When the units are cooling then they are working fine with good cooling across the coil face.

If I turn all units off and leave for a couple of minutes then turn back on they run fine for a length of time before the problems return.

There are no error codes!!!!

Any ideas?

Thanks