YORK YLAA — SYS 1 LOW SUCT PRESS SYS 2 LOW SUCT PRESS

The panel prints SYS 1 LOW SUCT PRESS SYS 2 LOW SUCT PRESS. The number after SYS is the system number, so the message is shown per refrigerant system — system 1 and system 2. This exact wording is the only form the manuals list for the message.

This is the low suction pressure cutout, System Fault Code 7, one of the chiller's system safeties. It is a software cutout that helps protect the chiller from an evaporator freeze-up should a system attempt to run with a low refrigerant charge or a restriction in the refrigerant circuit. When the suction pressure falls below the ramped cutout point, the system stops.

• Low refrigerant charge.
• A restriction in the refrigerant circuit.

• At system start the cutout is set to 10% of the programmed value and ramped up to the programmed cutout point over the next 3 minutes; for the first 30 s of system run time the cutout is completely ignored.
• After the first 3 minutes, if the suction pressure falls below the programmed cutout setting, a transient protection routine sets the cutout at 10% of the programmed value and ramps it up over the next 30 s; the system stops if the suction pressure falls below the ramped cutout.
• The manuals do not print the programmed cutout value itself.

This safety auto-resets: the system restarts automatically on the first and second fault and locks out on the third fault within 90 minutes. To clear the lockout, turn the system switch (under the OPTIONS key) OFF and then back ON.

The manual's warning on this safety: repeated starts after resetting a low suction pressure fault will cause evaporator freeze-up — whenever a system locks out on this safety, immediate steps should be taken to identify the cause.