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IOM 1242-2 • PATHFINDER
®
MODEL AWV CHILLERS
Ice Mode Start Delay
An adjustable start-to-start Ice Cycle Delay timer will limit the
frequency with which the chiller may start in Ice Mode. The
timer starts when the first compressor starts while the unit is in
Ice Mode. While this timer is active, the chiller cannot restart
in Ice Mode. The time delay is user adjustable. The Ice Cycle
Delay timer may be manually cleared to force a restart in Ice
Mode. A set point specifically for clearing the Ice Cycle Delay
is available, Clear Ice Delay. Cycling controller power will also
clear the timer.
Low Ambient Lockout
The operation of the chiller in response to OAT dropping below
the Low OAT Lockout set point is configurable if the Fan VFD
Configuration set point is set to 1st Fan VFD or All Fan VFD. In
that case, there are three options:
• Lockout and Stop – chiller will shut down and lockout
• Lockout only – chiller does not shut down running circuits,
will lock out circuits that are off
• Disabled – chiller does not shut down or lock out
If the Fan VFD Configuration set point is set to None, there is
no configuration and the chiller will always operate according
to the first option shown above. Descriptions of the operation
for each option are in the following sections.
Lockout and Stop Operation
If the OAT drops below the low ambient lockout set point and
the OAT sensor fault is not active, then low ambient lockout
is triggered. The unit will go into the pumpdown state if any
circuits are running. If no circuits are running the unit will go
directly into the off state. Once all circuits complete pumpdown,
the unit will remain in the off state until the lockout has cleared.
This condition will clear when OAT rises to the lockout set point
plus 2.5°C (4.5°F).
Lockout Only Operation
If OAT drops below the low ambient lockout set point and
any circuits are running, then those circuits will be allowed
to remain running and the unit will not enter the low ambient
lockout condition. Circuits that are not running will enter a
circuit level lockout condition when OAT drops below the
lockout set point. This condition will clear at the circuit level
when OAT rises to the lockout set point plus 2.5°C (4.5°F).
If the OAT is below the low ambient lockout set point, the OAT
sensor fault is not active, and no circuits are running, then low
ambient lockout is triggered. The unit will go directly into the
off state and will remain in the off state until the lockout has
cleared. This condition will clear when OAT rises to the lockout
set point plus 2.5°C (4.5°F).
Disabled Operation
When low ambient lockout is disabled, the unit will not enter
the low ambient lockout condition or shut down any running
circuits, regardless of the OAT.
BAS Annunciation
Low Ambient Lockout is not an alarm, but it can be
annunciated to the BAS as if it is one. When the Low OAT
Lockout BAS Alert set point is set to On and the low ambient
lockout is active, the following will occur:
• Chiller alarm status parameter will show alarm state
• Active Problem Alarm Code will be set to 16642
(assuming no higher code is active)
• Active Problem Alarm Index will be set to 65 (assuming
no higher index is active)
• Digital parameter AmbTempLow will show alarm state
• Intrinsic alarming will show low ambient temperature via
the LowOATemp object
Evaporator Pump Control
Only one source can be in control of the pumps at any given
time. Three evaporator pump control states for control of the
evaporator pumps:
1. Off - No pump on.
2. Start – Pump is on, water loop is being recirculated.
3. Run – Pump is on, water loop has been recirculated, and
circuits can start if needed.
T1 - Off to Start
- All of the following are required:
• Unit state = Auto
• Freeze protection started
T2 - Start to Run
- Requires the following to be true:
• Flow ok for time longer than evaporator recirculate time
set point
T3 - Run to Off
- Requires all of the following to be true:
• Unit state = Off
• Freeze protection not active
T4 - Start to Off
. - Requires all of the following to be true:
• Unit state = Off
• Freeze protection not active
T5 - Run to Start
. - Requires the following to be true:
•
Flow switch input is low for longer than the flow proof set
point
START
RUN
3
5
Summary of Contents for AWV008
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