YORK YVAA — Low discharge superheat cutout fault

The panel prints Low discharge superheat cutout fault for the affected circuit. In the manual's display description, the X is the system number, and the YYYYYYY field stands for the condition word: FAULT or LOCKOUT. FAULT means the system will restart on its own; LOCKOUT means it stays stopped until someone intervenes at the keypad.

This is a compressor-protection safety. It guards against liquid refrigerant flooding back through the economizer line when the flashtank level is high, and against excessive oil in circulation when the system carries an excess oil charge. Oil circulating with the refrigerant brings liquid refrigerant entrained in it back toward the compressor; that liquid drops out once it enters the compressor. When the discharge superheat falls below 2.8°C (5.0°F) for 5 minutes, the safety shuts the system down.

• Discharge superheat below 2.8°C (5.0°F) sustained for 5 minutes — the trip condition itself.
• A high flashtank level, which drives liquid floodback through the economizer line.
• An excess oil charge in the system, which puts excessive oil in circulation; the circulating oil carries entrained liquid refrigerant that drops out inside the compressor.

1. Note the position of the system economizer feed valve — closed (0%) or open greater than 0% — because the manual applies a different start-up ignore period to each case (10 minutes versus 5 minutes).
2. Look at the flashtank level: a high flashtank level is the condition behind liquid floodback through the economizer line.
3. Review the oil charge in the system: an excess charge is what produces excessive oil in circulation.
4. Follow the discharge superheat reading against the 2.8°C (5.0°F) threshold and how long it stays below it — the trip needs 5 minutes under either valve condition.

• Trip point: discharge superheat below 2.8°C (5.0°F).
• Trip delay: 5 minutes below the trip point.
• Start-up ignore period with the economizer feed valve closed (0%): the first 10 minutes of operation.
• Start-up ignore period with the economizer feed valve open greater than 0%: the first 5 minutes of operation.
• Anti-recycle timer after a FAULT shutdown: 120 seconds.

Recovery depends on how the message is shown. As FAULT, the system restarts by itself when the 120 second anti-recycle timer times out. As LOCKOUT, the system will not restart until the operator clears the fault using the keypad.