Specifications

51
JOHNSON CONTROLS
Form 201.28-NM1.EN.PED/CE (0211)
7
Compressor Heater Control
Each compressor has its own heater. The purpose of the
heater is to assure refrigerant does not condense in the
compressor. There is no oil sump, but refrigerant could
possibly condense in the rotors or the motor housing. The
heater will be OFF whenever the respective compressor
is running. As soon as the compressor shuts OFF, the
heater will turn ON as long as all motor temperature
sensors in the compressor read less than 70°C (158°F).
The heater will turn OFF, if any internal compressor
motor temperature sensor reads more than 71.1°C
(160°F).
Alarms
Each system has its own alarm. The Alarm output
is ON (dry contact closed) when no fault condition is
present and OFF (dry contact open) to indicate an alarm
situation. The Alarm will be activated (contacts open), if
any of the following are true.
• A System is faulted or inhibited from starting for
more than 5 seconds.
• The Unit is faulted or inhibited from starting for
more than 5 seconds.
• A System is locked out.
• The Unit is locked out.
• Power is removed from the chiller.
Chiller Run Contact
The Chiller Run dry contact is closed whenever any system
is running. It is open when all systems are shut OFF.
Flow Switch Control
A chilled liquid flow switch of suitable type MUST be
connected between Terminals 2 and 13 of 1TB to provide
protection against loss of liquid flow, which will cause
evaporator freeze-up if the chiller is permitted to run.
Remote Run / Stop
A Remote Run/Stop input is available for each system.
VSD OPERATION AND CONTROLS
The VSD Logic Board communications with the chiller
Chiller Control Board via comms and controls the VSD
functions. It converts the frequency and run commands
from the Chiller Control Board into the necessary
voltage and frequency commands to operate the inverter
section. It also controls the converter section of the drive
(AC Line to DC Bus conversion) by controlling the pre-
charge function.
The VSD Logic Board contains a 2nd microprocessor
(motor controller) that generates the PWM signals that
control the IGBT outputs in the inverter section of the
VSD.
The VSD Logic Board handles all of the VSD related
safeties, which includes motor current, BUS voltage, and
other safeties.
The VSD Logic Board reports shutdown information
back to the Chiller Control Board via the RS-485
communication link.
BASIC OPERATING SEQUENCE
Start Sequence and Loading
To initiate the start sequence of the chiller, the following
conditions must be satisfied before the precharge of the
DC Bus will take place:
• UNIT SWITCH must be ON.
• At least one System Switch is ON
• Run permissive inputs (Remote Cycling Contacts)
must be closed.
• No unit faults exist.
• No unit start inhibits exist.
• At least one system not faulted or inhibited.
• The Daily Schedule is calling for the chiller to run.
• The Flow Switch is closed.
• Leaving Chilled Liquid Setpoint is above the
Setpoint plus CR (Setpoint High Limit).
Once the precharge takes place, if the anti-recycle timer
is timed out the chiller control system on the Chiller
Control Board will select the number of compressors
to start and begin operation of the compressors. The
compressor(s) speed will be ramped to the minimum
start frequency and increase speed as needed in an effort
to regulate the leaving chilled liquid temperature to meet
the desired Setpoint.