I've been looking at a daikin vrv 3 the system is bringing up a u0 error. I'm trying to work out if it's low on refrigerant or the expansion device is playing up.
I've had it running on test and the suction pressure varies depending on compressor speed but average is about 6-8 bar but the discharge is only getting to 17-20 bar at full whack. The air off the indoor units is poor about 2 degrees lower than ambient on each one.

Now if it was an expansion issue wouldn't the suction pressure be either really low or really high depending how it's stuck. Also there is tons of valves on this so it's hard to see what one I'm after. It's one of the vrv units with 2 compressors 2 fans etc 2 sets of boards.
The compressors are ridiculously hot and the suction line is warm to ambient not cool the discharge is scolding hot.



I think it's possibly low on gas as opposed to it being an expansion issue but what's the best way to go about checking. I'm having a really off day today normally this would be easy but I mainly work on split systems and not vrvs.