TL;DR
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.
What you might see
- oil separator level high alarm
- oil carryover to refrigerant system
- oil return line temperature lower than expected
- evaporator performance declining
Likely causes
Oil return float trap stuck closed preventing oil from draining back to the sump
Oil return line partially blocked by a foreign particle or valve restriction
Oil viscosity too low at the operating temperature allowing excessive carryover
Compressor running at reduced capacity sending less gas flow through the separator
Required tools
- Refrigeration gauges
- IR thermometer (for oil return line check)
- LOTO kit
- PPE: refrigerant-rated gloves and face shield
Safety first
- Ammonia refrigerant is toxic and flammable. Work on the refrigerant-side oil return system requires a qualified refrigeration mechanic and appropriate PPE including supplied-air respirator for high concentrations.
- The oil separator and compressor discharge are at elevated pressure and temperature. Confirm system pressures before disconnecting any oil line.
Procedure
- 1
Check the oil separator level sight glass or electronic level reading. Confirm the alarm is genuine.[1]
- 2
Locate the oil return line from the separator to the compressor suction or sump. Check the line temperature. A cold return line indicates flow is blocked.[1]
- 3
Inspect the oil return float trap. Manually operate the test bypass valve to see if oil flows. A stuck-closed trap is the most common cause.
- 4
Check the oil return line for any closed isolation valves.
- 5
Verify the compressor oil injection temperature is normal. Low oil temperature increases viscosity and can prevent return flow at the float valve orifice.
- 6
If the evaporators have been running with elevated oil level for an extended period, plan an oil drain from the evaporator drain connections.
- 7
After clearing the oil return path, monitor the separator level for at least one hour to confirm oil is returning.
Sources
Frick (Johnson Controls) Frick RWB / RXF screw Industrial Refrigeration / Blast Freezer general technical documentation, Frick (Johnson Controls)
Frick RWB / RXF screw compressor general oil separator and oil return system procedures (general)
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