Johnson Controls YORK YVAM 0350, Operation & Maintenance Manual

Page: 23 / 162

• Condenser liquid flow is established
• No uncleared faults or start inhibits exist
Chiller operation
Upon start request, the following occur in sequence:
1. Chiller's system pump run contacts close
2. Variable speed drive pre-charges (approximately 12 seconds)
3. Variable speed drive pre-regulates (approximately 3 seconds)
4. Motor runs
The chiller varies capacity to maintain the leaving chilled liquid temperature setpoint by a specific
sequencing of optional hot gas bypass, variable geometry diffuser, and compressor speed.
Throughout capacity control, the compressor speed is maintained above the minimum required
for the prevailing head condition, to avoid surge. Otherwise, the device maintaining capacity is
controlled by a proportional-integral-derivative control based on leaving chiller liquid temperature.
Pressure and motor current overrides also apply as necessary to maintain operating limits.
The Input Current limit threshold value is determined from several settings, depending on the
chiller control source selected according to the following table.
Table 4: Input current limit threshold
Control source Active input current limit threshold
Local
Lowest of:
• Local Input Current Limit setpoint (% Input Job FLA)
• Pulldown Input Current Limit (when active)
ISN Remote Input Current Limit setpoint (comms)
Analog remote
Lowest of:
• Local Input Current Limit setpoint (% Input Job FLA)
• Analog Remote Input Current Limit setpoint
• Pulldown Input Current Limit (when active)
Digital remote
Lowest of:
• Local Input Current Limit setpoint (% Input Job FLA)
• Digital Remote Input Current Limit setpoint
• Pulldown Input Current Limit (when active)
Chilled liquid control settings
The following section contains information on the temperature control setpoint, automatic
temperature shutdown, and automatic temperature restart.
Temperature control setpoint
The temperature at which the chiller controls the chilled fluid leaving the evaporator must be
set by the Operator. The way it is selected depends if the Operator wants this value set locally or
modulated by a remote input.
23 YVAM Control Center