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SECTION 14 - ADAPTIVE CAPACITY CONTROL BOARD
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
JCI COMPANY CONFIDENTIAL
14
The potentiometer must be calibrated by a quali-
fied Service technician using a procedure in
TION 33 - SYSTEM CALIBRATION, SERVICE
SETPOINTS, AND RESET PROCEDURES
of
this manual. No speed reduction is permitted if
this calibration has not been performed.
•
Motor Speed –
This is the actual drive frequency
of 30 to 60 (50)Hz.
•
Surge Map –
This contains the Delta P/P, PRV po-
sition and motor speed that existed at the instant
of each previously encountered surge condition.
These parameters are stored as a 3-dimensional ar-
ray for each surge. The surge map is stored in the
ACC Board’s BRAM battery backed memory. The
following procedures are detailed in
SYSTEM CALIBRATION, SERVICE SETPOINTS,
of this manual. The
entire Surge Map can be printed by pressing the
Surge Map Print keypad key. Surge Map Points
can be automatically printed to an external printer
as they are plotted. The Surge Map can be cleared.
The Surge Map must never be cleared un-
less advised by the YORK factory.
The following conditions must be met before speed re-
duction is permitted:
• The PRV calibration procedure must have been
performed.
• Auto Speed Control Mode must be selected at the
keypad.
• Current Limit must not be in effect. When current
limit is in effect, Valid Point LED CR8 is illumi-
nated.
• The Chiller must have been running for greater
than 2 minutes.
• The Leaving Chilled Liquid Temperature must be
0.3°F and –0.6°F of the Leaving Chilled
Liquid setpoint. The Leaving Chilled Liquid Tem-
perature must be stable. Lowering the speed while
this temperature is unstable, would tend to increase
the instability. The microboard calculates the sta-
bility by comparing the Leaving Chilled Liquid
Temperature to the Leaving Chilled Liquid Tem-
perature setpoint to arrive at a rate of change value.
• Certain applications, such as short chilled liquid
loops, multi-pass evaporators, parallel chillers and
light load conditions can cause excessive Pre-ro-
tation Vane (PRV) movement resulting in leaving
chilled liquid temperature control instability. This
instability can be reduced by adjusting the Sen-
sitivity setpoint on the OptiView EVAPORATOR
Screen. The 50% selection reduces the magnitude
of PRV movement over the NORMAL selection
and the 30% selection reduces it even more. With
Flash memory card version C.MLM.01.06.xxx
(and later) or P compressors with C.MLM.04.02.
xxx (and later), and the 50% or 30% sensitivity is
selected, PRV movement is further reduced dur-
ing low load conditions with variable speed drive
as follows. When the PRV position is less than
25% and the Leaving Chilled Liquid Temperature
is within plus or minus 2.5 °F of setpoint, the max-
imum allowed vane pulse is limited to 3.5 seconds
at the 25% PRV position and 0.9 seconds at 0%
position. PRV positions in between have linearly
scaled maximums.
When the chiller is started, the speed is brought to 60Hz.
After it has been running for greater than 2 minutes and
the Leaving Chilled Liquid Temperature is 0.3
and –0.6°F of the Leaving Chilled Liquid Temperature
setpoint, the ACC Board evaluates if the speed can be
reduced. If there are no conditions above that would in-
hibit speed reduction, the ACC Board compares the real-
time Delta P/P, PRV Position and Motor Speed to the
3-dimensional arrays stored in the Surge Map. If the real-
time array does not match any previous surge condition,
the speed will be decreased 0.1Hz every 6 seconds until
it is within 1Hz of previously plotted surge condition
array in the Surge Map. It will then be decreased 0.1Hz
every 9 seconds until it’s to the lowest value allowed by
the Surge Map. If no plotted points are encountered, the
speed is lowered until a surge is encountered or a mini-
mum of 30Hz is reached.
The ACC Board uses two different methods of
Surge
Detection
; Delta P method and DC Link method.
Surge detection is only enabled while the chiller is run-
ning. In detecting a surge using the Delta P method,
the outputs of the Evaporator and Condenser Pressure
transducers are monitored to detect when the differ-
ence between these pressures (Delta P) drops transient-
ly toward Zero. This would be indicative of a surge. A
Surge Detected by the Delta P method must have all of
the following conditions occur within 5 seconds to be
considered a valid surge: