Carrier 17/19EX - Manual (Page 100)

If the configured lead chiller does not complete the start-up before the PRESTART FAULT
TIMER (user configured value) elapses, then the lag chiller shall be started and the lead chiller
will shut down. The lead chiller then monitors the start request from the acting lead chiller to
start. The PRESTART FAULT TIMER is initiated at the time of a start request. The PRESTART
FAULT TIMER’s function is to provide a timeout in the event that there is a prestart alert
condition preventing the machine from starting in a timely manner. The timer is configured
under Lead/Lag, found in the Equipment Configuration table of the Service menu.
If the lag chiller does not achieve start-up before the PRESTART FAULT TIMER elapses,
then the lag chiller shall be stopped and the standby chiller will be requested to start, if
configured and ready.
Standby Chiller Configuration and Operation
The configured standby chiller is identified as such by having the LEAD/LAG SELECT
configured to the value of ‘‘3.’’ The standby chiller can only operate as a replacement for the lag
chiller if one of the other two chillers is in an alarm (*) condition (as shown on the LID panel). If
both lead and lag chillers are in an alarm (*) condition, the standby chiller shall default to
operate in CCN mode based on its configured Occupancy Schedule and remote contacts input.