78 Product Manual PM WSC/WDC
j) Chilled water setpoint and reset temperature setpoint
k) Amp limit for manual and remote
l) History of last 8 failures with date and time plus critical sensor values
m) Unit status; start-up and shutdown sequence, operational status
3. The microprocessor shall either unload or shut down one or both compressors
during an abnormal condition. At a minimum the following safeties shall be
incorporated in the control system:
a) High and low discharge pressure
b) Low evaporator pressure
c) High discharge temperature
d) Chilled or condenser water pump failure
e) No evaporator or condenser water flow
f) High or low oil feed temperature
g) Low oil differential pressure
h) High motor temperature, low motor current
i) Surge-high suction superheat
j) Starter fault, no starter transition
k) Vanes open during start sequence
l) Sensor failure, specific to sensor
4. Controller shall hold leaving chilled water temperature to within 0.2°F. without
hunting, droop, or overshooting.
5. Controller shall be able to limit motor amps from 30 to 100 % of RLA based on a
keypad entry or by a remote 4-20mA DC signal.
6. The controller shall be able to reset chilled water temperature by controlling return
chilled water temperature or from a remote 4-20 mA DC signal.
7. Soft loading shall be provided to prevent the unit from operating at full load during
pulldown if desired.
8. A time clock shall be incorporated to allow daily timed starts and stops and to allow
for holiday and weekend schedule changes.
9. The control system shall have automatic restart after a power failure and not require
a battery backup for memory continuity. A battery shall be provided for the time
clock only.
10. The controller shall be capable of starting and stopping chilled water and condenser
water pumps. It shall also be capable of four-step control of cooling tower fans and
analog control of a tower bypass valve.
11. The microprocessor shall be capable of communicating to other units or a PC using a
twisted pair communication interface of RS-232 (100 feet) or RS-422/485 (5000 feet) or
with a 9600 baud modem.
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