On the display
The display reads MBC - Z12 LOW FREQUENCY DISPLACEMENT. The manuals print this single wording and list the message under the chiller's cycling shutdown messages.
What it means
The message reports excessive axial movement of the shaft. Behind it is a specific measurement: the MBC found the shaft sitting more than 100 µm away from its design running position along the axis, and that condition held over a 7 second window. Once the limit is crossed, the MBC opens its ESD Fault contacts and holds Levitation mode, keeping the motor shaft levitated.
Why it appears
- The trip cause is the measurement itself: axial shaft displacement above 100 µm from the design running position, persisting across a 7 second window.
Setpoints and thresholds
- Trip point: axial displacement from the design running position greater than 100 µm, evaluated over a 7 second window.
- Scale of the trip offset: roughly 1/3 of the axial air gap space up to the touchdown bearing.
- Release point: shaft displacement less than 100 µm.
Reset and restart
The message is released when the shaft displacement is less than 100 µm. The MBC leaves Levitation mode when it receives a de-levitate command over serial comms, or when the power on the VSD DC buss is depleted.
Questions engineers ask
What does MBC - Z12 LOW FREQUENCY DISPLACEMENT mean on a YORK YMC2?
The MBC has measured axial displacement greater than 100 µm from the design running position, held over a 7 second window — roughly 1/3 of the axial air gap space up to the touchdown bearing.
How is MBC - Z12 LOW FREQUENCY DISPLACEMENT cleared?
The message is released when the displacement is less than 100 µm. While it is active, the MBC stays in Levitation mode until it receives a de-levitate command over serial comms or the power on the VSD DC buss is depleted.
Which contacts open on the Z12 displacement trip?
On this trip, the ESD Fault contacts of the MBC open.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YMC2; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YMC2 messages: fault codes · YORK YMC2 documentation · YORK manuals