YORK YMC2 — MBC - V24 POSITION

The panel reads MBC - V24 POSITION. The manual lists it under the cycling shutdown messages for this chiller, and this wording is the only variant given.

The message reports the shaft out of position at the radial bearing at the opposite end from the impeller, on the V axis. The manual states that the MBC measured shaft displacement greater than 75 µm from center in the orthogonal radial axis designated V at the opposite-impeller-end radial magnetic bearing during Levitation or Rotation mode. A second manual for the model describes the same condition with a limit of 100 micron from center, in the same axis and at the same bearing, during Levitation or Rotation mode. The manual with the 75 µm figure relates that distance to approximately half of the air gap space to the touchdown bearing; the manual with the 100 micron figure calls it approximately 2/3 of the air gap space to the touchdown bearing. While the message is active, the MBC ESD Fault contacts open; the second manual words this as the MBC Fault contacts opening.

• The MBC measured displacement beyond its limit — greater than 75 µm from center, or greater than 100 micron in the second manual — in the radial axis designated V at the opposite-impeller-end radial magnetic bearing, during Levitation or Rotation mode.

• Shutdown threshold: shaft displacement greater than 75 µm from center (one manual) or greater than 100 micron from center (the other), in the V axis at the opposite-impeller-end radial magnetic bearing.
• Air-gap reference: the 75 µm limit sits at approximately half of the air gap space to the touchdown bearing; the 100 micron limit at approximately 2/3 of it.
• Release threshold: the shutdown is released when displacement is less than 75 µm, or less than 100 micron in the second manual.

The shutdown is released when the MBC measures displacement less than 75 µm from center, or less than 100 micron in the second manual's figures. Until then, the MBC remains in Levitation mode with the motor shaft levitated. It stays in Levitation mode until it is commanded to de-levitate over serial comms or, in the manual that gives the 75 µm figures, until the VSD DC buss power depletes.