YORK YK — abnormally low suction pressure

The panel shows abnormally low suction pressure; the manuals print the same message as Abnormally low suction pressure. It appears as one of the numbered symptoms in the troubleshooting operation analysis chart for the YK water-cooled centrifugal chiller.

The message reports that suction pressure has fallen below its normal range. The manual does not give the message one fixed meaning of its own; the operation analysis chart instead reads it together with the rest of the operating data. Three accompanying patterns are listed: a temperature difference between leaving chilled water and refrigerant in the evaporator greater than normal with high discharge temperature; the same temperature difference greater than normal with a normal discharge temperature; and a temperature of chilled water too low with low motor amperes. Each pattern points to a different cause, and one manual also lists insufficient charge of refrigerant without any distinguishing condition.

• Insufficient charge of refrigerant — one manual's chart states it more precisely as insufficient charge of refrigerant in evaporator.
• Variable orifice problem.
• Evaporator tubes dirty or restricted.
• Insufficient load for system capacity.

1. Read the accompanying operating data: whether the temperature difference between the leaving chilled water and the refrigerant in the evaporator is greater than normal, whether the discharge temperature is high or normal, and whether the chilled water temperature is too low with low motor amperes.
2. If the difference is greater than normal with a high discharge temperature, check for leaks and charge refrigerant into the system — this covers the insufficient charge of refrigerant in the evaporator.
3. For the same condition the chart also lists a variable orifice problem: remove the obstruction.
4. If the difference is greater than normal with a normal discharge temperature, clean the evaporator tubes — the cause is dirty or restricted tubes.
5. If the chilled water temperature is too low with low motor amperes, check the prerotation vane motor operation and the setting of the low water temperature cutout — the cause is insufficient load for the system capacity.

• Low water temperature cutout — its setting is checked when the chart's insufficient-load pattern applies (chilled water temperature too low with low motor amperes); the chart prints no value for this setting.