YORK YMC2 — MBC - POWER FAIL LANDING

The OptiView panel shows MBC - POWER FAIL LANDING, and this is the only wording the manuals give for the message. It belongs to the MBC Safety Shutdown group: the chiller manual describes it as a Safety Shutdown that is set on the panel, and the software release notes treat it as a fault that is cleared with the Clear Fault button.

This Safety Shutdown is set when the panel boots up after a power loss has occurred and the buffer data stored before the shutdown shows a motor speed greater than 0 — in other words, the motor was still rotating when the UPS power was lost. Seeing this message tells you the chiller went down on lost UPS power while the motor was turning, and the panel discovered this from its pre-shutdown buffer data when it came back up.

• The chiller lost UPS power while the motor was rotating: when the panel boots up after the power loss, the buffer data held from before the shutdown shows a motor speed greater than 0.

1. Determine the cause of the loss of UPS power.
2. Remedy that cause.
3. Open the MBC Details Screen and read the Power Fail Landing Counter.
4. If the counter is below 5, the chiller can be restarted — clear the fault with the OptiView panel clear faults button (see Reset).
5. If the counter is 5 or more, the unit is locked out and only a service technician may reset it, following the procedure in the Calibration and Troubleshooting Section.

• Power Fail Landing Counter (shown on the MBC Details Screen): below 5 — restart is allowed once the fault is cleared; 5 or more — lockout that a service technician must reset.
• Trigger condition: the pre-shutdown buffer shows motor speed > 0, meaning the motor was rotating when the UPS power was lost.

Restart is only possible after the cause of the UPS power loss has been determined and remedied. With the Power Fail Landing Counter below 5, the fault is cleared with the OptiView panel clear faults button, and the chiller can then be restarted. The manual states: If the Power Fail Landing Counter is < 5, the chiller can be restarted after the cause of a loss of UPS power is determined and remedied and the OptiView panel clear faults button is pressed. When the counter is 5 or more, lockout occurs; this lockout must be reset by a service technician according to the procedure in the Calibration and Troubleshooting Section. One software note applies: on earlier software the Clear Fault button did not always appear when this fault was set, and this has been corrected in the current software release.