Excessive Superheat

I have an issue on a custom built system used to cool a scientific process tank. The system has a Danfoss – Maneuorp compressor with the following specs:

Compressor: MTZ50-1
Code Number: MTZ50HK1VE MTZ50HK(B)1VE

33355 Btu/H; R134a; 60 Hz; 208 – 230 Volts 1/0 (187 – 253 VAC)
2504 Watts; 12.6 Amps; and a Cut-out temp of 230°F.

The system is built with cap tubes because the evaporator (four cap tubes feeding four sections – one each section) is located inside the process tank. The tank contains a gas, cooled by the evaporator, and consequently varies in pressure, which would affect at TEV. It is supposedly sized for low temp operation – around -10F.

The condenser is a plate type, water cooled unit, and does a remarkable job.

During initial cool down, starting with the system at ambient temp (75F) the system operates at only 75 psig head pressure, and around 3 psig suction. It does a respectable job of removing heat, but the Superheat is so excessive, that it will cause the compressor to cut out on high temperature – not head pressure. With head pressure, only in the 70’s, the compressor is only pulling 10.5 amps.

Readings: Process Tank atmosphere 75F; 78# head pressure; 2# suction pressure; High side gas discharge; 211F; Suction line gas temp 64F. After 15 minutes: Process Tank atmosphere 27F; 75# head pressure; 2”(vac) suction pressure; High side gas discharge; 223F; Suction line gas temp 27F. At this point, the compressor cuts out, requiring approximately 45 minutes to reset. This occurred 3 times today, and only once did the system make it down to 0F.

The system has a liquid receiver, and a suction line accumulator, and a sight glass in the HP line. Hot gas enters the condenser at the above listed temperatures, and exits at a respectable 68F. Water enters at 55F, and exits at 65F. This provides steady state liquid feed in the sight glass to the cap tube distributor. I have the ability to alter the water flow, which I have, and will marginally affect the head pressure, but obviously makes no affect on the superheat, nor the cooling efficiency of the system. I am able to reduce water flow to allow head pressure to climb to approx 125, but does not seem to help anything except to draw full load current of 12.5 amps.

I believe that is all the pertinent information I have on the system. Can anyone suggest what is wrong? It is charged with uncontaminated R134a.