requested to start . After the second chi ller is started and is running, the lead ch iller shall monitor
conditions and eva luate whether the capacity has r educed enough fo r the lead chiller t o sustain
the system alone. If the capacity is reduced enough for the lead chiller to sustain the CONTROL
POINT temperatures alo ne, then the operatin g lag chiller is stoppe d.
If the lead chiller is stopp ed in CCN mode for any reas on other than an alarm (*) c on dition,
then the lag and standby chi llers are stopped. If the configured lead c hi ller stops for and ala rm
condition, then the configured l ag chiller takes the lead chille r’s place as the lead chiller and t he
standby chiller serves as t he lag chiller.
If the configured lead ch ill er does not complete the start-up before t he P RE S T ART FAULT
TIMER (user co nfigured value) elapses, then the lag chi ller shall b e started and the lead ch iller
will shut down. The lead ch ill er then monitors th e s ta rt request from the ac ti ng lead chiller to
start. The PRESTA RT FAULT TIMER i s initiated at t he time of a st art request. The PRESTART
FAULT TIMER’s functio n is to provide a timeou t in the event that there is a pr es t art alert
condition preventi ng t he machine from start ing in a timely manner. Th e timer is configured
under Lead/Lag, foun d in t he Equipment Config uration table of the Ser v i ce menu.
If the lag chiller does not achieve start-up bef or e the PRESTART FAULT TI M E R ela pses,
then the lag chiller sha ll be stopped and the stand by chiller will be reque sted to start, if
configured and ready.