I need some help with a custom built refrigerated air dryer I'm working on. This thing is just over a year old, has two ckts with R-134a and is 100% redundant, only one ckt is needed for the load. Each ckt has a Copeland 6 cylinder compressor with two unloaders, remote air cooled condenser with two fans, liquid receiver, suction accumulator, oil separator, TXV and two Hot Gas By-pass valves. One HGB injects into the suction line just before the accumulator and the other HGB injects between the TXV and the evap. With the HGB's off and the compressor fully loaded, I had 0* to 1* superheat at the compressor, 3* subcooling and the sight glass was flashing. The glycol/water temp would drop to 30* and the suction would drop to 10 psi. I started adjusting the Emerson txv and ended up making 23 turns to get the SH up to 15* at the outlet of the evap. and yes, the bulb is attached to the suction line. I added 6 lbs of 134a, that was all I had at the time. The SC went up to 4* and I had mostly clear glass. The water temp drops from 56* to 35* in less than 10 min. with the comp fully loaded, so I would shut it down until the water warmed up. The unloaders are controlled by a digital temperature controller and was set to unload 2 cylinders at 35* and 2 more at 33* and the freeze stat which is another temp controller was set at 25*, this cycles the compressor off and on. A factory tech set-up the unit and had been back several times because the compressors were either in a block of ice or the suction line at the compressors would be too hot to keep your hand on. I talked to the manufacturer and they said to keep the HGB valve closed that injects into the accumulator, adjust the other one to open at 28 psi, adjust the unloaders for 46* and 45* with a 5* diff. and set the condenser fan cycling controls for fan-1 at 175 psi cut-in, 125 psi cut-out. Fan-2 at 200 psi cut-in, 175 psi cut-out. I feel that the fan cycling pressures would be too high. With the unloaders set as stated, the suction still drops to 13 psi. I then set the HGB to start opening at 28 psi and it sounds like it is fully open at 25 psi. I still have to go back and add refrigerant to this ckt and replace the compressor on ckt #1, it is shorted to ground. I think it got too hot from both HGB's being open and the unloaders set too low. I feel that the evaporator barrel is too big, not enough water flow through it which makes the suction drop.
What should I have on the following:
1) What glycol/water temp should I have
2) What temp should I set the unloaders for
3) What should the freeze stat be set for.(this cycles the comp off & on)
4) What should I set the fan cyc controls cut-in and cut-out at, (two fans)
5) What air temp drop should I have (compressed air)
6) For some reason do dryers have low Subcooling.