TL;DR
High discharge temperature on a screw compressor shortens rotor and bearing life. Check oil injection temperature, capacity slide valve, and suction superheat before adjusting setpoints.
What you might see
- discharge temperature above normal operating range
- high-temp alarm on compressor panel
- oil cooler outlet temperature elevated
- compressor capacity reduced
Likely causes
Oil injection temperature too high from an undersized or fouled oil cooler
High suction superheat from a refrigerant distribution or expansion valve problem
Slide valve stuck at partial capacity increasing compression ratio
Refrigerant overcharge or contamination changing vapor state at suction
Required tools
- Refrigeration gauges (suction and discharge)
- IR thermometer
- Oil sample kit
- Clamp ammeter
Safety first
- Ammonia refrigerant systems require OSHA PSM and EPA RMP compliance. Work on the refrigerant side requires a qualified refrigeration mechanic.
- High-pressure refrigerant at elevated temperature is present at the compressor discharge. Wear appropriate PPE including face shield and refrigerant-rated gloves.
- Lock out the compressor start circuit before working on any mechanical components including oil filters and slide valve actuators.
Procedure
- 1
Record the suction pressure, discharge pressure, oil temperature, and discharge temperature from the compressor panel.[1]
- 2
Calculate the compression ratio (discharge pressure absolute divided by suction pressure absolute). A high ratio increases discharge temperature.[1]
- 3
Check the oil cooler refrigerant or water supply. Fouled or undersized oil coolers cannot maintain oil injection temperature.
- 4
Inspect the oil filter differential pressure. A clogged oil filter reduces oil flow and raises discharge temperature.
- 5
Measure the suction superheat at the compressor suction service valve. High superheat (above 10 to 15 K) indicates an expansion valve problem upstream.
- 6
Check the capacity slide valve position indicator. A valve stuck at partial capacity can cause abnormal discharge conditions.
- 7
If operating parameters are all normal but discharge temperature is high, suspect refrigerant quality or contamination. Take an oil sample for analysis.
Sources
Frick (Johnson Controls) Frick RWB / RXF screw Industrial Refrigeration / Blast Freezer general technical documentation, Frick (Johnson Controls)
Frick RWB / RXF screw compressor general discharge temperature and oil system maintenance procedures (general)
More guides for Frick (Johnson Controls) Frick RWB / RXF screw
How to diagnose bearing vibration on a Frick RWB / RXF screw compressor
Rising vibration on a screw compressor bearing signals imminent failure. Take an oil sample, trend the vibration readings, and schedule a bearing inspection at the next opportunity.
How to fix an oil separator high level on a Frick RWB / RXF screw compressor
High oil level in the separator means oil is not returning to the compressor. Check the oil return line and float trap, then verify the evaporators are not oil-logged.
Stop fixing the same fault twice.
Dovient turns guides like this into your team's shared playbook, with AI that catches recurring issues before they break the line.