McQuay AGS 225D, Руководство по эксплуатации

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14 OM AGSD-1
Off Conditions
Power is supplied to the power section of the electric panel. The standard power connection
is two (or three on models 330 to 450) separate sources, one to each circuit. Optionally, the
power may be supplied to a single power connection, either a power block or optional
disconnect switch.
With power supplied to the unit, 115 VAC power is applied through the control fuse F1 to
the compressor heaters, HTR1 and HTR2, evaporator heater, and the primary of the 24V
control circuit transformer.
CAUTION
Compressor heaters must be on for at least 12 hours prior to start-up
to avoid compressor damage.
The 24V transformer provides power to the MicroTech II controller and related components.
With 24V power applied, the controller will check the position of the front panel system
switch Q0. If the switch is in the "stop" position, the chiller will remain off, and the display
will indicate the operating mode to be
OFF: Unit Switch. The controller will then check
the pumpdown switches. If any of the switches are in the "stop" position, that circuit’s
operating mode will be displayed as
OFF: Pump Down Switch. If the switches for both
circuits are in the "Stop" position, the unit status will display OFF: All Circuits Disabled .
If the remote start/stop switch is open the chiller will be OFF: Remote Switch . The chiller
may also be commanded off via communications from a separate communicating panel such
as a BAS protocol interface. The display will show
OFF: BAS Disable if this operating
mode is in effect.
If an alarm condition exists which prevents normal operation of both refrigerant circuits, the
chiller will be disabled and the display will indicate
OFF: Unit Alarm . If the control mode
on the keypad is set to "Manual Unit Off," the chiller will be disabled and the unit status
will display
OFF: Keypad Disable .
Alarm
The red alarm light in back of the left arrow key on the controller will be illuminated when
one or more of the cooling circuits has an active alarm condition which results in the circuit
being locked out or a unit alarm is active and manual reset is required. If only a circuit
alarm is active, the remaining circuits will operate as required. Events (low-level
occurrences) will not cause the key to light.
Start-up
If none of the above "off" conditions are true, the MicroTech II controller will initiate a start
sequence and energize the chilled water pump output relay. The chiller will remain in the
WaitForFlow mode until the field-installed flow switch indicates the presence of chilled
water flow. Once flow is established, the controller will sample the chilled water
temperature and compare it against the Leaving Chilled Water Setpoint, the Control Band,
and the Start-up Delta-Temperature, which have been programmed into the controller’s
memory.
If the leaving chilled water temperature is above the Active Chilled Water Setpoint plus the
adjustable Start-up Delta-T, the controller will select the refrigerant circuit with the lowest
number of starts as the lead circuit and initiate a start request. The circuit controller will
open the EXV and start the compressor. A green light under the Enter key on the circuit
controller will illuminate to indicate that the compressor is running.
If additional cooling capacity is required, the controller will activate additional cooling. As
the system load increases, the controller will start the lag refrigerant circuit when the lead
circuit reaches 75%, or some other capacity limit is reached, and the interstage timers are
satisfied. The compressors and capacity control solenoids will automatically be controlled
as required to meet the cooling needs of the system.