On the display
The panel prints this message as VSD - Low DC bus voltage in the medium voltage variable speed drive cycling fault messages, and as VSD - Low DC Bus Voltage in the variable speed compressor drive cycling fault messages. The manuals print it both ways; work from the spelling your panel shows.
What it means
The drive monitors all of its DC bus voltages continuously. On the medium voltage drive, the trip occurs when any one of those voltages falls below 1,238 VDC — 75% of 1,650 VDC — continuously for 30 ms, and the drive then initiates a cycling shutdown. On the variable speed compressor drive, the trip occurs when the DC bus voltage drops below the limit set for the drive, and the drive initiates a system shutdown. The threshold and the shutdown type therefore depend on which of the two drive groups your chiller carries.
Why it appears
- A severe sag in the incoming power to the drive — the manual names this as a common cause of the low DC bus voltage shutdown.
Setpoints and thresholds
- Medium voltage drive: trip threshold 1,238 VDC, which is 75% of 1,650 VDC, sustained for 30 ms.
- 380 VAC, TM/VSD/LVSD drives: 414 VDC.
- 400 VAC, TM/VSD/LVSD drives: 414 VDC.
- 460 VAC, TM/VSD/LVSD drives: 500 VDC.
- 575 VAC, TM/VSD/LVSD drives: 600 VDC.
- All HYP model drives: 735 VDC.
Reset and restart
For the medium voltage drive's cycling shutdown, clearing is automatic: Messages automatically clear when the fault condition no longer exists; if the chiller was running when the fault occurred, it automatically restarts.
For the variable speed compressor drive version, which shuts the system down, the manual describes no reset step.
Questions engineers ask
What does VSD - Low DC bus voltage mean on a YORK YK?
The DC bus voltage dropped below the limit, so the drive shut the chiller down — a cycling shutdown on the medium voltage drive, a system shutdown on the variable speed compressor drive.
What is the low DC bus voltage trip threshold?
On the medium voltage drive the threshold is 1,238 VDC — 75% of 1,650 VDC — held continuously for 30 ms. For all model drives it depends on line voltage: 414 VDC at 380 or 400 VAC, 500 VDC at 460 VAC, and 600 VDC at 575 VAC for TM/VSD/LVSD drives, and 735 VDC for all HYP model drives.
Why did my YORK YK trip on low DC bus voltage?
The manual gives one common cause: a severe sag in the incoming power to the drive.
Will the chiller restart by itself after VSD - Low DC bus voltage?
For the medium voltage drive's cycling shutdown, yes — the message clears automatically once the fault condition no longer exists, and a chiller that was running when the fault occurred automatically restarts.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YK; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YK messages: fault codes · YORK YK documentation · YORK manuals