I am working on a chiller manufacturing company as equipment designer. We recently started manufacturing chillers. The total capacity of the chiller that we have problem is r134a 600kW with screw compressor. The system is equipped with economizer(Liquid line going into plated Heat exchanger and going out to the electronic expansion valve before evaporator. At the same time a thermostatic expansion valve is connected from liquid line to the plated heat exchanger going out to the economizer port of the compressor)

We have system equipments of liquid line dryer, microchannel condensers, axial fans, shell and tube evaporator, screw compressor, and economizer kit.

The system is perfectly vacuumed. the system is designed in 50C(12,12bar gauge) condensing temperature and (2,25bar gauge) evaporation temperature. All equipment sizings are done with the softwares of the manufacturers.(which i dont find any errors to it.) the water inlet outlet is 7-12C and the design outdoor ambient is 35C.

We have comissioned the unit in our test bench at 23C ambient temperature. i loaded the compressor to its maximum load(since it is a stepless modulated compressor) opened up the electronical expansion valve to %100 and started loading refrigerant. I manually brough the discharge pressure to 12 bar by closing the fans manually and watched the suction pressure increase at this condition. However no matter how much i charge the refrigerant it does not reach above 1,8 bars. after somepoint it starts to increase the discharge pressureto 13 bar levels. which i think that is due to liquid backing up in condensers. The temperature of the liquidline becomes 24-27C which also proves the subcooling. i checked if there is a liquid line restriction that reduces the flow in the EXV however i checked the liquid line elements such as valves and dryers, there is only 0,05 bar difference which is quite normal.

By the way there is constant bubbleing on the sight glass after plated heat exchanger in the liquid line. That is also very strange. if the condensers are fed and filled with liquid isn't it supposed to be liquid only?(the temperature of the liquid line piping is 24C on 13bar)

The superheat in %100EXW with %100 load of compressor is around 20K (which our design rate is 5K) at this condition.

So basically summarizing:
Compressor Amp drawn: normal
Suction pressure:low
Discharge pressure:normal-high
Sight glass:bubbling

I am suspicios of undersized EXV but i chose it with quite large capacity(over%20)

I need some wisdom urgently. I can share additional info if required.

note that economiser plated heat exchanger pressure loss is 55kpA(0,5bar)