Low Hi and Low pressure on VRF Hitachi

[ewgeny]

Hi, all. One of our VRF systems has a problem. A week ago call us that one of systems is not heating. Ambient temp was 5-6 deg. cels. The system is 30HP with 6 compresors (1 inv. and 5 on/off). Hi pressure was near 18-19 bars, low pressure 2 bars, and going down. Both EXV ware 20 % open, and going closer to 10%. Compressors at the start run 3 of 6, but for 30 min. turn off 2 of them, and the Invertor one is slowing down.
Errors wich shows are:
Low pressure fall protection
Discharge gas Superheat falling retry
Pressure ratio control
High pressure fall protection

Temp on the top of the compressors is not more than 40 deg. cels. (normally its 80-100 deg)

Buth when the weather get better like 15-16 deg. cels., evrything looks fine.

So I think that is insufficiente refrigerant (R410A), but I'll glad to hear if there is any other viewpoint, becouse recovrering is not that easy part and the other reason is that we can't find any leak....for now.

Thank You futurful and I'm sorry for my English

[Thermatech]

The system has target HP of 30 bar & will normally run at 7 to 8 bar suction depending on ambient temp & outdoor coil frosted condition.

The outdoor unit looks at the very low suction pressure & ramps down on LP fall protect safety stratagy.

Suggest call up live HP & LP sensor data on the outdoor control board LED display & compare with gauge reading just to make sure HP & LP sensors are providing accurate data.

For ball park judgement of refrigerant charge look for discharge superheat of 25 to 45.
In heating at 30 bar discharge you are looking for discharge temp off the compressor head at 75 to 95 deg C.

SOG is prime suspect so a good place to start is recover refrigerant to see how much is left in the system.

[ewgeny]

What is SOG?
I check the pressures with gauges and it's OK.
Is there another option that You have in mind?

Thank's

[Thermatech]

S short
O of
G gas

[ewgeny]

We recover nearly 41 kg. (39.5 need to be) and there are 2-3 bar pressure. Tomorrow will recover the rest of the refrigerant, but it will be more than has to be. My question is what is the range of propperly charget system in percent? Have anyone a suggestion where to search for the problem? I've to remind that last day, before begin to recover te refrigerant, wash warm 16-18 deg. cels. and teh system works properlly by temp. and pressure. Thanks in advance.

[ewgeny]

The problem is from Low Pressure Sensor. It shows -2 bar, which is imposibble. Now we are watting a delivery of new one.