YORK YCAV — UNIT VSD LOGIC BOARD FAILURE

The panel prints UNIT YYYYYYYY VSD LOGIC BOARD FAILURE. The characters the manual shows as YYYYYYYY, standing between "UNIT" and "VSD LOGIC BOARD FAILURE", indicate a FAULT condition, which restarts, or a LOCKOUT. All listings of this safety in the manuals use this single wording, and the message is one of the unit's VSD safeties (faults).

This is a software-generated VSD safety. When the control issues voltage and frequency commands, the PWM generator must acknowledge receipt of the command; the fault means the system microprocessor did not receive that handshake within 1.5 seconds of issuing the command, and the unit trips. It is a unit fault for all units: if it occurs while the chiller is running, all systems shut down immediately. The safety is only active during precharge and during running of a compressor — it is not active when all compressors are shut down and the precharge is disabled.

• The PWM generator does not acknowledge the voltage and frequency commands within 1.5 seconds of issue, so the system microprocessor receives no handshake and the unit trips.

• Handshake window: the PWM generator must acknowledge the voltage and frequency commands within 1.5 seconds of issue.
• Active window: during precharge and while a compressor is running.
• Auto-restart timer: 120-second anti-recycle timer.
• Lockout threshold: 3rd fault within 90 minutes.

This is an auto-restart safety: after a trip, the unit restarts by itself once the 120-second anti-recycle timer times out. If the fault recurs, it locks out on the 3rd fault in 90 minutes. A lockout is not cleared by the auto-restart — On lockout, cleared using the keypad.