York YCAV0157-0267, Installation Operation & Maintenance

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170
JOHNSON CONTROLS
FORM 201.21-NM1 (616)
OPERATION
OPERATING CONTROLS
Anti-recycle Timer
A typical 5 or 10 minute anti-recycle timer is not
necessary to allow compressor motor cooling, due to
the VSD’s ability to provide a low current inrush start.
The system does utilize a fixed 120 second anti-recycle
timer to prevent short cycling of systems and to allow
positioning the Feed and Drain Valves to a zero (closed)
position by the Flash Tank Drain and Feed Valve Con-
troller in the event of a power failure.
On power-up of the control panel, the anti-recycle timer
for each system will be set to 120 seconds and must time
out before a compressor is allowed to start.
Whenever a system starts, the anti-recycle timer for all
systems will be set to 120 seconds and will count down
from the time the motor starts. The timer must time out
before another compressor is allowed to start.
Whenever a system shuts down, the anti-recycle timer
for that system will be set to 120 seconds. The timer
must time out before the system is allowed to restart.
Evaporator Pump Control
The evaporator pump dry contacts are energized when
any of the following conditions are true:
· If a Low Leaving Chilled Liquid Fault occurs.
· Whenever a compressor is running.
· The Daily Schedule is ON and the Unit Switch is
ON.
Even if one of above is true, the pump will not run if
the panel has been powered up for less than 30 seconds
or if the pump has run in the last 30 seconds to prevent
pump motor overheating.
Evaporator Heater Control
The evaporator heater is controlled by ambient air
temperature. If no systems are running and the
ambient temperature drops below 40°F, the heater is
turned on. If no systems are running and the temperature
rises above 45°F the heater is turned off. Whenever a
system is running, the evaporator heater is turned off.
Both evaporator heater outputs will always be turned on
and off together. An under voltage condition will keep
the heater off until full voltage is restored to the system.
Pumpdown Control
The VSD assures a smooth slow compressor start.
As a result of this, neither pumpdown on start-up or
pumpdown on shutdown is required. The Drain and
Feed Valves will close when a compressor stops. This
is a similar to a liquid line solenoid valve closing on a
conventional chiller.
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 compres-
sor 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 <158°F. The heater will
turn off, if any internal compressor motor temperature
sensor reads >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 should be activated (contact 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.