YORK YK — Oil - Low Temperature Differential

The panel shows Oil - Low Temperature Differential. The manuals print the same text as Oil - Low temperature differential and OIL - LOW TEMPERATURE DIFFERENTIAL. The control treats it as a start inhibit — a condition that prevents a chiller start; in earlier software versions it could also act as a cycling fault.

The message compares the oil sump temperature with the condenser saturation temperature: when the oil sump temperature minus the condenser saturation temperature falls below 40.0°F (4.4°C), the condition is set and the chiller is kept from starting. The manual's tables phrase the check at different oil-pump states — the display-message table sets it instantly when the difference is below 40.0°F (4.4°C) with the oil pump not running, while the start-inhibit list sets it when the difference is below 40.0°F while the oil pump is running. In the current software version the condition is checked only when the chiller is stopped; previously it was checked while the chiller was stopped and during the first 10 seconds of Pre-lube, and it is no longer checked during Pre-lube.

• Oil sump temperature less than 40.0°F (4.4°C) above the condenser saturation temperature.
• Running at low load conditions for extended periods, which lets the oil temperature get too low — the origin the manual gives for the condition.

1. Read the two values the condition compares — the Oil Sump Temperature and the condenser saturation temperature — and find the difference; the condition exists below 40.0°F (4.4°C).
2. Look at the recent operating pattern: extended running at low load conditions is the situation the manual names when the oil temperature drops too low.
3. If the chiller has been shut down, note for how long — earlier software versions prevented a start when the shutdown was 30 minutes or less and the oil temperature was less than 30°F (16.7°C) above the saturated temperature, or when the shutdown exceeded 30 minutes and the difference was less than 40°F (22.4°C); the comparison uses the condenser saturated or sump saturated temperature depending on the software version.
4. On P, Q and H9 compressor chillers with software V21, open the Oil Sump Screen and confirm the OIL RETURN MIN setpoint — the key appears there when the CHILLER STYLE/COMPRESSOR TYPE setpoint on the Operations Screen is set to P, Q or H9 compressor.

• Inhibit threshold: oil sump temperature minus condenser saturation temperature below 40.0°F (4.4°C).
• Earlier-software start-prevention thresholds: 30°F (16.7°C) for a shutdown of 30 minutes or less, and 40°F (22.4°C) after more than 30 minutes.
• OIL RETURN MIN setpoint (software V21, P, Q and H9 compressor chillers): programmable from 80.0°F to 110.0°F, default 95.0°F.
• Solenoid action: while the compressor runs, the oil return solenoid is closed (de-energizing the K12 relay) when the Oil Sump Temperature is below OIL RETURN MIN, and opened (energizing K12) when it is above OIL RETURN MIN + 7°F; during coastdown and start-up it follows standard logic and remains closed — for 1 minute after system run at start-up.

The manuals give no separate reset procedure. The release rule is: Released when the set criteria is no longer true. The message therefore clears on its own once the oil sump temperature rises far enough above the condenser saturation temperature, and since the current software checks the condition only while the chiller is stopped, a start is possible again once the difference leaves the inhibit range.