Daikin VRVII excessive oil return or defrost?

[Ladiesman217]

Two condensers and eight fan coils. I have a couple FCU's that are always in heating mode. They heat fine for half an hour to 45 minutes. Then stat reads standby and the third pipe is cold. Outdoor air temp in the 50's.

[The Viking]

First thing to check is the charge,
Reclaim the refrigerant, weigh it and compare with how much it could have.

:cool:

[Ladiesman217]

I don't think it's charge related. It has been running this way since I changed one of the compressors. At the time of the compressor change, I did an extensive leak search while inspecting and measuring line lengths. System held pressure test for days and pulled below 500 microns.

[Ladiesman217]

I will add that condensing pressures and temps looked good on service checker. Maybe I could force all FCU's into cooling and observe the individual coil superheats. I just don't want to recover the roughly 60 pounds of refrigerant unless it's the last resort.

[The Viking]

OK,
More telling, start all the indoor units in Heat mode and observe the discharge temperature.
If it goes anywhere near 100 C (212 F) your system is likely to be short of charge, if it doesn't reach 60 C (140 F) you are likely looking at an overcharged system.
But this gives a very rough estimate of charge, best is to reclaim and weigh.

:cool: