On the display
The control center displays VSD - PHASE A INPUT DCCT OFFSET. The manuals list this message among the chiller's cycling shutdown messages, and it is raised by the VSD at the moment precharge begins.
What it means
When the VSD begins precharge, the output of the input current Direct Current Current Transformers (DCCT) is evaluated to confirm that each one is reading zero current when no current is flowing through the DCCT. The first value of each DCCT output voltage is compared against an offset threshold level of ±24.4 mV. If the DCCT offset at initialization exceeds this threshold, this shutdown is generated. If the threshold is not exceeded, the VSD instead takes an average of eight readings on each DCCT output and uses that average for DCCT offset compensation. This message therefore means the zero-current check on the input current sensing failed right at precharge initiation.
Why it appears
- The zero-current output value of an input current DCCT was above the threshold: the DCCT offset present at initialization exceeded ±24.4 mV when the precharge command was asserted.
Setpoints and thresholds
- Offset threshold level checked at precharge initialization: ±24.4 mV.
Reset and restart
This is a cycling shutdown. The manual states: The chiller will automatically restart when the cycling condition clears.
No separate manual reset step is described for this message.
Questions engineers ask
What does VSD - PHASE A INPUT DCCT OFFSET mean on a YORK YMC2?
The VSD found that an input current DCCT was not reading zero at precharge: its output voltage at initialization was above the ±24.4 mV offset threshold, so the shutdown was generated.
How do I clear the VSD - PHASE A INPUT DCCT OFFSET fault on a YMC2?
No manual reset is described. It is a cycling shutdown, and the chiller will automatically restart when the cycling condition clears.
Why does the DCCT offset shutdown appear at precharge?
Upon the assertion of a precharge command, the output voltage of each DCCT that senses the input current is monitored, and the first value is compared against the ±24.4 mV offset threshold. Exceeding that threshold at initialization generates this shutdown.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YMC2; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YMC2 messages: fault codes · YORK YMC2 documentation · YORK manuals