YORK YMC2 — MBC - OVERSPEED FAULT

The panel prints the message MBC - OVERSPEED FAULT. The manuals list it among the Safety Shutdown messages of this model, and they print the display text in only this one form, so there are no alternate wordings of this message to watch for.

This Safety Shutdown is set when the MBC determines that the rotor speed exceeds the programmed setpoint for 0.1 seconds continuous. The rotor speed is transmitted to the MBC from the VSD, so the shutdown acts on the speed signal the MBC receives. Doc 160.78-O2 gives the programmed setpoint as 458 Hz and states that the MBC ESD Fault contacts open; doc 160.84-OM1 gives the setpoint as 360 Hz and states that the MBC Fault contacts open. While the shutdown is active, the MBC remains in Levitation mode with the motor shaft levitated. Per doc 160.78-O2 this levitated state continues until the MBC is commanded to de-levitate over serial comms or the VSD DC buss power depletes; doc 160.84-OM1 mentions only the de-levitate command over serial comms.

• Rotor speed above the programmed setpoint — 458 Hz per doc 160.78-O2, 360 Hz per doc 160.84-OM1 — held for 0.1 seconds continuous; this is the only trigger condition the manuals give for this shutdown.
• The speed value the MBC evaluates is the signal transmitted from the VSD; the manuals list no further causes for MBC - OVERSPEED FAULT.

• Overspeed setpoint: 458 Hz (doc 160.78-O2).
• Overspeed setpoint: 360 Hz (doc 160.84-OM1).
• Duration above the setpoint that sets the shutdown: 0.1 seconds continuous.

The shutdown is released when the speed signal no longer exceeds the setpoint, which the manuals say should occur when the chiller is stopped. Once the condition is released, the chiller can be started after the CLEAR FAULTS button on the OptiView panel is pressed: The chiller can be started when the condition is released and the OptiView panel CLEAR FAULTS button is pressed. Both manuals describe this same release and restart sequence.