On the display
The panel shows LOW SUCTION PRESSURE FAULT. The manual lists no other wording for this message. It is a safety lockout: the system has stopped because the suction pressure fell below its cutout point.
What it means
The control stopped the system on the low suction pressure safety because the suction pressure dropped below the programmed cutout setting. The manual cautions against running the unit with a low refrigerant charge or a restriction in the refrigerant circuit, and warns that repeated starts after resetting this fault will cause evaporator freeze-up. Whenever the system locks out on this safety, the manual calls for immediate steps to identify the cause.
Why it appears
- The suction pressure cutouts are adjusted improperly.
- The refrigerant charge is low.
- The filter dryer is fouled.
- The TXV is defective.
- The flow of chilled liquid through the cooler is reduced.
- The suction pressure transducer or low pressure switch, or its wiring, is defective.
- The LLSV is defective.
What to check
- Before restarting, identify the cause of the lockout — repeated starts after resetting this fault will cause evaporator freeze-up.
- Adjust the suction pressure cutouts to the recommended settings.
- If the charge is low, repair the leak if necessary and add refrigerant.
- Change the filter dryer core.
- Replace the TXV.
- Check the GPM (the manual points to its Operational Limitations section); check the operation of the pump, clean the pump strainer, and purge the chilled liquid system of air.
- Replace the suction pressure transducer or low pressure switch, or the faulty wiring — the Service section of the manual gives the pressure/voltage formula for this check.
- Replace the LLSV.
Setpoints and thresholds
- At system start, the cutout is set to 10% of the programmed value and ramps up to the programmed cutout point over the next 3 minutes. If the suction pressure falls below the ramped cutout point at any time during those 3 minutes, the system stops.
- The cutout is completely ignored for the first 30 seconds of system run time, to avoid nuisance shutdowns — especially on units that use a low pressure switch in place of the suction pressure transducer.
- After the first 3 minutes, if the suction pressure falls below the programmed cutout setting, a
transient protection routine
is activated: the cutout is set back to 10% of the programmed value and ramps up over the next 30 seconds.
Questions engineers ask
What causes LOW SUCTION PRESSURE FAULT on a YORK YLAA?
The manual lists these causes: improperly adjusted suction pressure cutouts, low refrigerant charge, a fouled filter dryer, a defective TXV, reduced flow of chilled liquid through the cooler, a defective suction pressure transducer or low pressure switch or its wiring, and a defective LLSV.
Can I keep resetting and restarting the chiller on this fault?
No. The manual warns that repeated starts after resetting a low suction pressure fault will cause evaporator freeze-up, and that immediate steps should be taken to identify the cause whenever the system locks out on this safety.
How long is the low suction pressure cutout ignored at startup?
The cutout is completely ignored for the first 30 seconds of system run time. It then starts at 10% of the programmed value and ramps up to the full programmed cutout point over the next 3 minutes.
What is the transient protection routine?
After the first 3 minutes of running, if the suction pressure falls below the programmed cutout setting, the control sets the cutout back to 10% of the programmed value and ramps it up over the next 30 seconds.
Messages next to this one
Source
Written from the manufacturer's manuals for the YORK YLAA; every number and designation on this page is checked against them before publication. The row of the manual this message comes from:
All YORK YLAA messages: fault codes · YORK YLAA documentation · YORK manuals