On our ZR630 screw compressor we are facing the following issue:

The temperature reading of Element 2 outlet rises near the max value (455 deg F) during unload time, and it falls during loading. We have cross checked the outlet pipe temperature with a surface thermometer and found that the pipe temperature actually falls while unloaded  whilst the HMI indication rises towards the trip point.

We have done maintenance in almost everywhere; From instrument side, we have tested and replaced the element 2 outlet sensor and cable with new ones, we have tested the unit with a new programmed ELEKTRONIKON HMI, we have checked the wirings and those seems to be good. From mechanical side, we have checked at the cooling water flow and pressure, the oil level is ok, new filters have been installed, but despite all those changes the same problem is still there.

Below are the compressor parameters readings:

Compressor Outlet
127 psi; Max = 218 psi

DP Air Filter
0.0 psi; Min = -0.8 psi

Oil Pressure
38.0 psi; Min 17.4 psi

Intercooler
31 psi

Compressor Outlet Temp
88 deg F

Element 1 Outlet
321 deg F; Max = 455 deg F

Element 2 Inlet
92 deg F; Max = 158 deg F

Element 2 Outlet
341 deg F; Max = 455 deg F

Cooling Water In
91 deg F

LP Cooling Water Out
98 deg F

Cooling Water Out
98 deg F

Oil Temperature
100 deg F; Max = 158 deg F

Element 1 Inlet
89 deg F

I would appreciate any suggestion that could help to fix this issue.