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226
FORM 160.54-M1
ISSUE DATE: 10/25/2019
SECTION 26 - VARIABLE GEOMETRY DIFFUSER
JCI COMPANY CONFIDENTIAL
JOHNSON CONTROLS
HIGH LIMIT Setpoint. Press the WARNING RESET
key in SERVICE access level to clear. After it is cleared,
the VGD returns to normal operation.
The extreme stall condition is not checked under the
following conditions:
• While the VGD is in Manual Control Mode.
• While the VGD is fully closed (VGD Limit
Switch closed).
• While the Pre-rotation Vanes position is greater
than the PRV VGD Inhibit setpoint.
MANUAL OPERATION
The VGD can be manually controlled from the VARI-
ABLE GEOMETRY DIFFUSER Screen in SERVICE
access level, whether the chiller is running or not.
Pressing the OPEN, CLOSE or HOLD key invokes
manual operation and the VGD Control Mode displays
MANUAL. Each time the OPEN or CLOSE keys are
pressed, the respective output is energized and the as-
sociated LED illuminates. Pressing the HOLD key
causes the Hold LED to illuminate and the VGD to be
held in its present position. Pressing the AUTO key in-
vokes automatic operation and AUTO is displayed as
the Control Mode.
SETPOINTS
The following setpoints are entered on the VARIABLE
GEOMETRY DIFFUSER SETPOINTS Screen. They
require SERVICE access level.
• Enable/Disable - Enables or Disables the VGD
feature. Default is Disabled. Chiller must be
stopped to change this setpoint.
•
Surge React (1-30 seconds; default 5) - Specifies
the duration of the close pulse applied to the VGD
in response to a surge.
• PRV Offset (0-5%; default 3) – If the VGD con-
trol is in the Stall Waiting state and the Pre-ro-
tation Vanes position increases by more than this
value, the Probing state will be entered. If the
PRV Offset is set to 0%, the Stall Waiting state is
performed based only on the Probe Wait setpoint
interval.
• Probe Wait (0.5-15 minutes; default 10) – Speci-
fies how long the VGD control remains in the
Stall Waiting or Surge Waiting states before enter-
ing the Probing state.
•
Open Pulse (1-9 seconds; default 2) – Specifies
the length of the open pulse applied to the VGD
during 10 second periods while in the Probing
state.
• High Limit (0.5 to 1.2 VDC; default 0.6V (0.8V
with software version C.OPT.01.22.307 and ear-
lier)) – Specifies the Stall Detector Board output
voltage that represents an acceptable amount of
stall noise. Above this value is unacceptable.
The minimum difference between the High Limit
setpoint and the Low Limit setpoint is 0.1 VDC. If a
Low Limit setpoint is entered which is less than 0.1
VDC below the High Limit setpoint, the High Limit
setpoint is adjusted so that it is 0.1 VDC above the
newly entered Low Limit value.
• Low Limit (0.4-0.8 VDC; default 0.5V (0.6V with
software version C.OPT.01.22.307 and earlier))
– in the Stall Reacting State, the VGD is driven
closed until the Stall Detector Board output volt-
age decreases to this level.
The minimum difference between the High Limit
setpoint and the Low Limit setpoint is 0.1 VDC. If a
Low Limit setpoint is entered which is less than 0.1
VDC below the High Limit setpoint, the High Limit
setpoint is adjusted so that it is 0.1 VDC above the
newly entered Low Limit value.
• Extreme Stall Duration (10 to 20 minutes; default
10 minutes)(Software version C.MLM.01.14.
xxx (and later) or C.OPT.01.14.306 (and later))–
Specifies the maximum allowed time an extreme
stall condition can exist before the Variable Ge-
ometry Diffuser operation is disabled (and driven
full open) to protect it from damage.
• PRV VGD Inhibit (40% -100%; default 100%;
95% with software version C.OPT.01.22 and ear-
lier) (Software version C.MLM.01.14.xxx (and
later) or C.OPT.01.14.306 (and later)) - While
the re-rotation vanes position is greater than this
setpoint, extreme stall conditions are not checked,
the VGD control is inhibited and the VGD will be
pulsed open according to the Open Pulse setpoint.
While this is in effect, PRV POSITION OVER-
RIDE is displayed as Control Status.