YORK YK — LOW OIL PRESSURE

On the control center's 40 character alphanumeric display the shutdown reads MON XX:XX AM - LOW OIL PRESSURE, where MON is the day of the week and XX:XX AM is the time. The manuals also print the message in the example form DAY 10:30 AM - LOW OIL PRESSURE. This is a safety shutdown, and the cause of every system shutdown is preserved in the control center memory until the system is reset or restarts, so the message stays available for viewing on the keypad display.

LOW OIL PRESSURE is a safety shutdown on low differential oil pressure. It appears when either of two things happens: the oil pressure has decreased to 15 PSID (103.4 kPa) while the chiller is running, or the pressure never achieved 25 PSID (172.4 kPa) before the compressor start during the oil pump pre-lube run. In the chiller starting sequence the compressor starts after the first 50 seconds of operation. The differential pressure is sensed by two pressure transducers, and the lubrication protection description names the high and low oil pressure transducers (OP) and the oil temperature sensor (RT3) as the devices that sense any malfunction in the lubrication system.

• Oil pump running in the wrong direction — the troubleshooting chart pairs this cause with "low oil pressure displayed on control center; compressor does not start."
• Oil pump not running — the manual directs you to troubleshoot the electrical problem with the oil pump VSD.
• Unusual starting conditions, i.e. oil foaming in the reservoir and piping due to lowered system pressure — given for the symptom where the compressor starts, normal oil pressure develops, the pressure fluctuates for a short while and the compressor stops on oil pressure cutout with LOW OIL PRESSURE displayed.
• Burned out oil heater — listed under the same fluctuating-pressure symptom.
• Dirty oil filter element — the maintenance section says that if the unit is shutting down on Low Oil Pressure (OP), change the oil filter element; the same passage calls out restricted oil lines, passages, or dirty oil filters.

1. Read the oil pressures on the control center data display, which shows HOP = XX.X PSIG and LOP = XX.X PSIG — the low oil pressure (LOP) as measured at the oil sump — and compare them with the 15 and 25 PSID thresholds listed below.
2. If the message is displayed and the compressor does not start, check the rotation of the oil pump (Electrical Connections) — a pump running in the wrong direction is the listed cause.
3. If the oil pump is not running, troubleshoot the electrical problem with the oil pump VSD.
4. If the compressor started with normal oil pressure that fluctuated for a short while before the oil pressure cutout, drain the oil from the compressor and charge new oil into it — the manual's cross-reference for this job is "Charging The System With Oil."
5. Replace the oil heater if it is burned out.
6. Change the oil filter element and examine it for aluminum particles. Aluminum gas seal rings can contact the impeller, so some particles are expected during initial start-up and the first several months of operation; if aluminum particles continue to accumulate, contact Johnson Controls. Form 50.40-O1 gives the guidelines for oil change intervals, oil quality, operational quantities, application and storage.

• Trip point while running: oil pressure decreased to 15 PSID (103.4 kPa).
• Start permissive: 25 PSID (172.4 kPa) must be achieved before the compressor start, during the oil pump pre-lube run.
• Restart permissive: the chiller is allowed to restart when the pressure increases to 25 PSID — Form 160.52-O1 prints the equivalent as 173 kPa, Form 160.49-O1 as 172.4 kPa.
• Pre-run time: the compressor starts after the first 50 seconds of operation.
• Anti-recycle timer (non-VSD Chillers only): initiated after the 50 seconds of pre-run time, it runs for 30 minutes after the compressor starts.

The restart is manual. The chiller is allowed to restart once the oil pressure increases to 25 PSID. The manual's instruction is: To restart chiller, press COMPRESSOR switch to STOP/RESET position and then to the START position. The shutdown cause is retained in the control center memory until the system is reset or restarts. Note that if the chiller shuts down during the 30 minute anti-recycle cycle that begins when the compressor starts, it cannot be started until the timer completes the 30 minute cycle.