YORK YMC2 — MBC SHUTDOWN - REQUESTING FAULT DATA

The control center shows the message exactly as MBC SHUTDOWN - REQUESTING FAULT DATA. It is a short-lived message: serial communications with the MBC start up every 2 seconds, so it normally stays on the display for only a few seconds. The panel then switches to the particular MBC fault message that applies.

The MBC has shut the chiller down, but at the moment this message appears the control center does not yet know why: the fault cause has not yet come over the serial communications link from the MBC. The control center's microboard therefore asks the MBC control board, over that link, to send the cause. This message covers that short wait, and once the answer arrives the display moves on to the specific MBC fault message.

• The MBC shutdown itself is the trigger: the message appears because the cause of that shutdown has not yet reached the control center over the serial link.
• One manual describes the path the shutdown takes: The MBC shuts down the chiller by opening the MBC Emergency Shutdown (ESD) contacts (located on the MBC control board and connected between TB6-15 and TB6-53 in the control center).
• The other manual gives the same event through different contacts: The MBC shuts down the chiller by opening the MBC Fault contacts (located on the MBC control board and connected to TB3-70 in the control center).

1. Let the exchange run: the control center and the MBC start their serial exchange every 2 seconds, so the request for the fault cause goes out while this message is on the display.
2. Read the MBC fault message that replaces this one — it carries the fault cause the control center was waiting for.

Both manuals place this message in the cycling shutdown messages group. The action given for it reads: Cycling shutdown: the chiller will automatically restart when the cycling condition clears. On the display the message clears by itself: after a few seconds the panel shows the specific MBC fault message instead.