YORK YMC2 — MBC - W24 POSITION

The control center displays the message MBC - W24 POSITION. The manuals print it in this form only, so this is the exact text to expect on the panel. It belongs to the unit's cycling shutdown messages, and the manual text treats it as a shutdown rather than a warning.

MBC - W24 POSITION means that the MBC has measured shaft displacement greater than the trip threshold from center in the orthogonal radial axis designated W at the opposite-impeller-end radial magnetic bearing, during Levitation or Rotation mode. How far that is from the touchdown bearing is printed two ways: approximately half of the air gap space to the touchdown bearing at the 75 µm threshold, and approximately 2/3 of the air gap space to the touchdown bearing at the 100 micron threshold. When the limit is exceeded, the MBC fault contacts open — the manual that gives the 75 µm value calls them the MBC ESD Fault contacts. The shaft does not drop at once: the MBC remains in Levitation mode with the motor shaft levitated until it is commanded to de-levitate over serial comms or, in that manual, until the VSD DC buss power depletes.

• Shaft displacement greater than the trip threshold from center in the orthogonal radial axis designated W at the opposite-impeller-end radial magnetic bearing, while the machine is in Levitation or Rotation mode. The manuals give no other cause and no contributing conditions for this message.

• Trip threshold, one manual: displacement greater than 75 µm from center in the W axis — approximately half of the air gap space to the touchdown bearing.
• Trip threshold, other manual: displacement greater than 100 micron from center in the W axis — approximately 2/3 of the air gap space to the touchdown bearing.
• Release point: the shutdown is released when displacement is less than 75 µm in the first manual, and less than 100 micron in the second.

No manual reset procedure is described for this message. The shutdown releases itself when the measured displacement falls back below the value that tripped it — less than 75 µm in one manual, less than 100 micron in the other. Until then the MBC stays in Levitation mode with the motor shaft levitated, and it leaves Levitation mode only when commanded to de-levitate over serial comms or, per the manual with the 75 µm value, when the VSD DC buss power depletes.