YORK YMC2 — CONTROL PANEL - LOSS OF CONTROL VOLTAGE

The panel prints CONTROL PANEL - LOSS OF CONTROL VOLTAGE. The manuals give this single wording only — no other spelling or variant is listed — so this exact text is what appears on the display. The message is documented in the cycling shutdown messages and the safety shutdown messages groups of the manuals.

The message means that the control power input signal at I/O board TB3-81 was low for 1 second continuous. The operations manual for this model words the same monitored input as the line power input signal at TB3-81, so the two manuals name one signal at the same terminal differently. The panel watches this signal to determine when the digital inputs are affected by a panel or line power loss versus an actual condition for their devices — it is how the control center separates a power-loss situation from a genuine device event reported on a digital input.

One limitation printed with the fault matters when you read the display: This fault is not expected on an actual loss of microboard power from the critical load bus, because the processor will be off before the fault delay. A true loss of microboard power takes the processor down before the 1-second detection time elapses, so this message is not the expected response to that event.

• The control power input signal at I/O board TB3-81 was low for 1 second continuous. (The operations manual prints the identical cause as a low line power input signal at the same terminal.)
• An actual loss of microboard power — including from the critical load bus — is not an expected trigger of this message, because the processor will be off before the fault delay.

• Monitored input: control power (line power) input signal at I/O board TB3-81.
• Fault trigger: the signal low for 1 second continuous.
• Restart behaviour: cycling (auto-restart after power failure) or safety (manual restart after power failure) shutdown, per control center configuration.

The restart path depends on the control center configuration. The operations manual states that this message can indicate a Cycling (auto-restart after power failure) or Safety (manual restart after power failure) shutdown, depending upon control center configuration. For the cycling path, the other manual's fault table gives the automatic recovery: The chiller will automatically restart when the cycling condition clears. The safety path is the manual-restart case after a power failure. No separate key-by-key reset procedure is described for this message.