YORK YCAV — SYS X LOW DISCHARGE SUPERHEAT

The panel shows SYS X YYYYYYYY LOW DISCHARGE SUPERHEAT, where X stands for the number of the affected system. YYYYYYY indicates a "FAULT" condition or "LOCKOUT", so the status field tells you whether the safety has simply tripped or has escalated to a lockout. The same message is also listed without the status field, as SYS X LOW DISCHARGE SUPERHEAT.

This is the Low Discharge Superheat Cutout Fault, a system safety that produces a controlled ramped shutdown rather than an immediate stop. It helps protect the compressor primarily from liquid floodback through the economizer line due to a high flash tank level, and from liquid floodback through the suction line in conjunction with the low superheat safety. The safety is ignored for the first 5 minutes of compressor operation, so it can only trip once the compressor has run beyond that point.

• After the first 5 minutes of compressor run time, the discharge superheat falls below 10.0°F and remains there for 5 minutes — this is the trip condition the manual gives for this safety.
• The low discharge superheat reading points to liquid floodback into the compressor: primarily through the economizer line when the flash tank level is high, and through the suction line in conjunction with the low superheat safety.

• Trip threshold: discharge superheat below 10.0°F, sustained for 5 minutes.
• Ignore window: the safety is ignored for the first 5 minutes of compressor operation.
• Anti-recycle timer: 120 seconds before an automatic restart.
• Lockout rule: 3 faults on the same system within 90 minutes.

After a FAULT, the system restarts automatically when the 120-second anti-recycle timer times out. Once 3 faults have occurred on the same system within 90 minutes, the message shows LOCKOUT and the system will not restart until the operator clears the fault using the keypad; the manual states the lockout is cleared by cycling the system switch OFF and ON.