YORK YVAA — SYS X LOW DIFF OIL PRESSURE

The panel reads SYS X YYYYYYYY LOW DIFF OIL PRESSURE, printed in short form as SYS X LOW DIFF OIL PRESSURE. X is the system number, so the message tells you which system of the chiller tripped. YYYYYYYY is the status word that follows the message on the display: it reads FAULT or LOCKOUT, and which one is shown decides how the system comes back (see Reset). The manual groups this message with the system safeties (faults).

This is the Low Differential Oil Pressure Cutout. It protects the compressor from low oil flow and insufficient lubrication, and it ensures the compressor is pumping sufficiently to push oil through the oil cooling circuit and the internal compressor lubrication system. The value it watches is the differential between the oil pressure and the suction pressure. When that differential falls below the cutout, the system does not drop out hard: it shuts down with a controlled ramped shutdown.

• The differential between the oil and suction pressure falls below the cutout that is active at that moment. This cutout is not one fixed number — it is ignored during the first part of run time and then ramped upward as the run continues, with the ramp duration set by ambient temperature (values under Settings).
• Nuisance-trip window: the manual introduces the case of another compressor being brought on while the running compressor is ramped down to 5 Hz, and it employs a 30 second safety bypass below 50 Hz during rampdown specifically to prevent nuisance low oil differential trips in that situation.

• Ignored for the first 60 seconds of run time.
• Ramped cutout: after the first 60 seconds the cutout is ramped linearly from 0 barg to 2.09 barg (0 psid to 30 psid) over 5 to 10 minutes, based on ambient temperature: above 10 °C — 5 minutes; above 7.2 °C — 6 minutes; above 4.4 °C — 7 minutes; above 1.6 °C — 8 minutes; above 1.1 °C — 9 minutes; 1.1 °C or below — 10 minutes.
• Low-speed bypass: below 50 Hz during rampdown a 30 second safety bypass applies — this is what covers the moment another compressor is brought on and the running compressor is ramped down to 5 Hz.

On the trip itself the system shuts down with a controlled ramped shutdown. What happens then depends on the status word on the display. FAULT: the system restarts automatically once the 120 second anti-recycle timer times out; the auto-reset is not unlimited, because on the third fault within 90 minutes the system locks out — the manual's instruction is to cycle the respective system switch OFF and ON to clear. LOCKOUT: the system will not restart until the operator clears the fault using the keypad.