YORK CodePak AC Undervoltage

[chengfw]

I am getting an AC Undervoltage message on a 330 ton centrifugal chiller unit. The technical manual states that this message is indicative of the unit running at less than 15% current for a certain period of time and then the unit shuts down as if there is no power (and hence no current). The unit is running at 95% capacity when this happens and then a few minutes later the unit starts back up again. What else could be generating the AC Undervoltage message?

[sedgy]

hi chengfw,
have you tested the incoming voltage? what is it on each pair of the 3 ph ,= sedgy

[chengfw]

I have put a Fluke scopemeter on the incoming voltages and all of the internal control and signal voltages and they are all within acceptable ranges and remain stable when the unit shuts down and gives the AC Undervoltage readout. The technical manual states that the AC Undervoltage readout results from control relay R1 dropping out, normally from a control signal from the microboard when it senses little or no current to the motor. The manual also states that the relay could drop out with the resulting message if anything else causes a loss of control power but I am not getting any power losses. I do not know what in the programming drives that relay output but when it drops out I am getting 12VDC at the output from the microboard which tells me it is something in the program driving that relay to release but I do nor knot what in the program would do this. The technical manual is surprisingly vague considering the size of it.

[serviceman]

MON XX:XX AM - AC UNDERVOLTAGE - AUTOSTART

The chiller is shut down because the MicroComputer Control
Center was in RUN mode, displaying

SYSTEM RUN - LEAVING TEMP CONTROL

but the motor current was less than 10% FLA for 25 continuous
seconds. This is indicative of an AC undervoltage
condition that has caused the start relay (1R) in the
MicroComputer Control Center to de-energize. This condition
is checked when the MicroComputer Control Center
goes into RUN mode. This condition can also be caused
by failure of any component that would cause a loss of
the start signal from the Control Center. In essence, this
check assures that the compressor is running when the
Control Center is displaying

[chengfw]

Serviceman, I read that in the technical manual and have already confirmed that the unit is running at 95% FLA when the unit shuts down and nothing else in the circuit to the start relay (1R), such as the high pressure switch, is causing a loss of the start signal. When the unit shuts down the signal to the relay output board is indicating that the microboard is driving the shutdown but I do not know what would cause the microboard to do this.