YORK YK — Evaporator - Low pressure - Smart freeze

The panel prints the message as Evaporator - Low pressure - Smart freeze. The same protection also appears as Evaporator - Low pressure - Smart Freeze, with a capital F. The two spellings mark two stages of one trip: the lowercase spelling is the cycling fault in the cycling fault list, while the capitalized spelling is the safety fault in the safety fault messages list. On controls with software YOPT.01.03A.3085 and earlier, the lowercase-named message is itself listed as a safety fault.

For Y.OPT.01.04.3085 and later, the message means that the evaporator pressure has decreased to the capacity control low pressure override with the Warning - Evaporator - Low press limit active, and capacity control has not been able to increase the evaporator pressure within 2 minutes. As a cycling fault it shuts the chiller down if it was running and then lets it restart by itself. When this cycling fault has happened three times within 90 min, the control sets the safety fault Evaporator - Low pressure - Smart Freeze, and the chiller stays off until that fault is cleared.

On controls with software YOPT.01.03A.3085 and earlier, Evaporator - Low pressure - Smart freeze is a safety fault with a different trigger: Smart Freeze protection is enabled and has shut down the chiller because the evaporator refrigerant temperature has been below the Smart Freeze threshold for greater than the allowable number of seconds before freezing. The number of seconds allowed is based on how far the evaporator refrigerant temperature is below the freeze threshold.

• Evaporator pressure fell to the capacity control low pressure override while the Warning - Evaporator - Low press limit was active, and capacity control could not raise the evaporator pressure within 2 min (cycling fault, Y.OPT.01.04.3085 and later).
• Three occurrences of the Smart freeze cycling fault within 90 min set the safety fault Evaporator - Low pressure - Smart Freeze.
• Evaporator refrigerant temperature below the Smart Freeze threshold for greater than the allowable number of seconds before freezing (safety fault, YOPT.01.03A.3085 and earlier).

• 2 min: the time capacity control is given to increase the evaporator pressure out of the low pressure override before the cycling fault is set.
• Three times within 90 min: the count of cycling faults that sets the safety fault.
• Freeze threshold, software YOPT.01.03A.3085 and earlier: 32.8°F (0.4°C) when the evaporator refrigerant temperature sensor RT7 is enabled; 34.0°F (1.1°C), the evaporator saturation temperature derived from the evaporator pressure transducer, when RT7 is not enabled.

The cycling fault needs no manual action: if the chiller was running, it automatically shuts down and then restarts. The safety fault Evaporator - Low pressure - Smart Freeze is cleared by hand once the pressure condition has gone. You can restart the chiller after the evaporator pressure has increased above the override threshold and the Clear button is pressed next to the listed event on the Systems Details Screen. On the other control center the same step is described as pressing the CLEAR FAULT key on the display. No separate clear procedure is printed for the earlier-software safety fault of the same name.