CIrCUIT fUnCTIons
www.DaikinApplied.com 71 IOM 1206-7 • TRAILBLAZER
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MODEL AGZ CHILLERS
T6 – Preopen to Off
Any of the following are required:
• Unit State = Off
• Unit State = Pumpdown
• Circuit switch is open
• Circuit mode is disable
• Circuit Rapid Stop alarm is active
• Circuit Pumpdown alarm is active
Pumpdown Procedure
Pumpdown is performed as follows:
• If multiple compressors are running, shut off the
appropriate compressors based on sequencing logic and
leave only one running
• Turn off hot gas output and liquid line output
• Keep running until evaporator pressure reaches the
pumpdown pressure, then stop compressor
• If evaporator pressure does not reach pumpdown
pressure within two minutes, stop compressor
Low Ambient Starts
A low OAT start is initiated if the condenser refrigerant
saturated temperature is less than 29.5°C (85.1° F) when the
rst compressor starts. Once the compressor starts the circuit
is in a low OAT start state for a time equal to the Low OAT
Start Time set point. During Low OAT Starts, the freezestat
logic for the low evaporator pressure alarm as well as the low
evaporator pressure hold and unload alarms are disabled. The
absolute limit for low evaporator pressure is enforced and the
low evaporator pressure alarm should trigger if the evaporator
pressure drops below that limit. In addition if the evaporator
pressure is less than the Low Evap Pressure Unload set point
during the low POAT start, no addition al compressors can
start on that circuit even though the hold and unlaod events are
disabled at this time.
When the Low OAT Start Timer has expired, if the evaporator
pressure is greater than or equal to the Low Evaporator
Pressure Unload set point, the start is considered successful
and normal alarm and event logic is reinstated. If the
evaporator pressure is less than the Low Evaporator Pressure
Unload set point when the Low OAT Start Timer expires, the
start is unsuccessful and the compressor will shutdown.
Multiple Low Ambient Start attempts are allowed. On the third
failed Low Ambient Start attempt, the Restart Alarm is triggered
and the circuit will not attempt to restart until the Restart alarm
has been cleared.
The restart counter should be reset when either a startup is
successful, the Low OAT Restart alarm is triggered, or the unit
time clock shows that a new day has started.
Circuit Status
The displayed circuit status should be determined by the
conditions in the following table:If more than one status is
enabled at the same time, the hightest numbered status
overrides the others and is displayed.
# Status Conditions
1 Off:Ready Circuit is ready to start when
needed.
2 Off:Cycle Timers Circuit is off and cannot start
due to active cycle timer on all
compressors.
3 Off:All Comp
Disable
Circuit is off and cannot start
due to all compressors being
disabled.
4 Off:Keypad
Disable
Circuit is off and cannot start due
to circuit enable set point.
5 Off:Circuit Switch Circuit is off and circuit switch is
off.
6 Off:Alarm Circuit is off and cannot start due
to active circuit alarm.
7 Off:Test Mode Circuit is in test mode.
8 Preopen Circuit is in preopen state.
9 Run:Pumpdown Circuit is in pumpdown state.
10 Run:Normal Circuit is in run state and running
normally.
11 Run:Evap Press
Low
Circuit is running and cannot load
due to low evaporator pressure.
12 Run:Cond Press
High
Circuit is running and cannot load
due to high condenser pressure.
Compressor Control
Compressors should run only when the circuit is in a run or
pumpdown state. They should not be running when the circuit
is in any other state.
Starting a Compressor
A compressor should start if it receives a start command from
the unit capacity control logic.
Stopping a Compressor
A compressor should be turned off if any of the following occur:
• Unit capacity control logic commands it off
• An unload alarm occurs and the sequencing requires this
compressor to be next off
• Circuit state is pumpdown and sequencing requires this
compressor to be next off
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