Johnson Controls YORK YMC2 Operation And Maintenance Manual

• Remotely through digital inputs in digital or analog remote mode, but the local keypad start
must be pressed initially to enable the run permissive
• Remotely using the SC-EQUIP in BAS (ISN) remote mode, but the local keypad start must be
pressed initially to enable the run permissive
To start the chiller press the start button on the home screen on the display panel. In local control
source, the chiller then starts. In remote ISN, analog, digital, or modem, a remote start command
must also be provided to the correct input connection.
When the control is changed to local mode from any other source, it remains in run if already
running or it remains in stop if already stopped. A hardware safety stop button is also located on
the side of the panel.
The chiller starts if the following conditions are met:
• The leaving chilled liquid temperature is above the setpoint
• Chilled liquid flow is established
• Condenser liquid flow is established
• No uncleared faults or start inhibits exist
Chiller operation
Upon start request, the following occur in sequence:
1. The system pump run contacts close
2. VSD pre-charges (approximately 12 s)
3. VSD pre-regulates (approximately 3 s)
4. Motor runs
The chiller will vary 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 Table 7.
Table 7: 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
Temperature control setpoint
The temperature to which the chiller controls the chilled fluid leaving the evaporator must be set
by the operator. The way it is selected depends whether the operator wants this value set locally or
modulated by a remote input.
YMC
2
Mod B with OptiView Control Center
22

Johnson Controls YORK YMC2 Specifications

General

Brand	Johnson Controls
Model	YORK YMC2
Category	Chiller
Language	English