YORK YMC2 — VSD - DC BUS PRE-REGULATION

The panel reads VSD - DC BUS PRE-REGULATION — the manual prints it only this way, with no spelling variants. It is one of the chiller's cycling shutdown messages, and it appears during the start sequence, in the phase the manual calls pre-regulation: after the boost rectifier's closed-loop control has been enabled and while the VSD is bringing the DC link voltage up to its setpoint.

The DC link voltage did not attain a value within ±50 V of the DC link voltage setpoint — 750 V for YMC2, a setpoint defined by the motor and line voltages — within 2 seconds after the boost rectifier's closed-loop control was enabled. Pre-regulation therefore did not complete inside the time the VSD logic board allows. While the fault is present, the VSD logic board disables the boost rectifier's IGBT gating signals.

• The DC link voltage failed to come within ±50 V of the DC link voltage setpoint (750 V for YMC2) within 2 seconds after the boost rectifier's closed-loop control was enabled — this is the only cause the manual gives for the message.

• DC link voltage setpoint: 750 V for YMC2, defined by the motor and line voltages.
• Attainment window: within ±50 V of that setpoint.
• Time allowed: 2 seconds after the boost rectifier's closed-loop control is enabled.
• Retry wait: 10 seconds before the fault is cleared and another pre-charge may start.
• Attempt limit: up to three consecutive pre-charge-related or pre-regulation-related faults before the lockout safety shutdown.

The manual describes no reset action at the panel — the fault clears on its own timer. The VSD logic board shall time 10 seconds before clearing the fault and allowing another pre-charge to start. The VFD's fan(s) and water pump(s) remain energized during that wait. Because the unit failed to complete pre-regulation, it must repeat pre-charge in order to attempt another pre-regulation. Up to three consecutive pre-charge-related or pre-regulation-related faults are allowed; after the third, the safety shutdown message VSD - DC BUS PRE-REGULATION LOCKOUT is generated.