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Adaptive Capacity Control Board
The Surge Map must never be cleared
unless ad vised by the YORK Factory.
The following conditions must be met be fore speed
re duc tion is permitted:
• The PRV calibration procedure must have been
per formed.
• Auto speed control mode must be selected at the
Key pad.
• Current Limit must not be in effect. When cur-
rent limit is in effect, Valid Point LED CR8 is
il lu mi nat ed.
• The Leaving Chilled Liquid Temperature must be
with in +0.3 and –0.6ºF of the Leaving Chilled Liq-
uid Setpoint.
• The Chiller must have been running for >2 min-
utes.
• The Leaving Chilled Liquid temperature must be
sta ble. Lowering the speed while this tem per a ture
is un sta ble, would tend to increase the instability.
The Microboard calculates the sta bil i ty by com-
par ing the Leaving Chilled Liq uid Tem per a ture to
the Leav ing Chilled Liq uid Tem per a ture Setpoint
to ar rive at a rate of change value. This value is
then compared to the programmed Stability Limit
Setpoint. If the rate of change exceeds the Sta bil i ty
Lim it Setpoint val ue, the Microboard sends a fl ag to
the ACC Board. In response, the ACC Board starts
a 60 sec ond tim er. VALID POINT LED CR8 will
be il lu mi nat ed and speed de creas es are pro hib it ed
until the timer has elapsed. Also, when making
the tran si tion from Manual speed control Mode to
Auto Mode, the sta bil i ty timer is started, preventing
speed re duc tion for 60 seconds. The Sta bil i ty Limit
setpoint is pro grammed over the range of 1000 to
7000, by a qual i fi ed Service Technician us ing the
procedure in the "System Calibration, Ser vice
Setpoints and Re set Procedures" sec tion of this
book. This val ue is a relative value that rep re sents
magnitude of sta bil i ty. Higher values cor re spond to
decreasing sen si tiv i ty. Default value of 4500 will
provide prop er op er a tion in most applications.
• Certain applications, such as short chilled liquid
loops, multi-pass evaporators, parallel chillers and
light load conditions can cause ex ces sive Pre-rota-
tion Vane (PRV) movement resulting in leaving
chilled liquid temperature con trol instability. This
instability can be reduced by adjusting the SEN-
78
SITIVITY Setpoint on the Optiview Evaporator
Screen. The 50% se lec tion reduces the magnitude
of PRV move ment over the NORMAL selection and
the 30% se lec tion reduces it even more. With Flash
Mem o ry Card version C.MLM.01.06.xxx and later
or "P" com pres sors with C.MLM.04.02.xxx and
later, and the 50% or 30% sensitivity is selected,
PRV movement is further reduced during low load
conditions with variable speed drive as follows:
When the PRV position is < 25% and the Leaving
Chilled Liquid Temperature is within + 2.5 ºF of
Setpoint, the max i mum allowed vane pulse is lim-
ited to 3.5 seconds at the 25% PRV position and 0.9
seconds at 0% po si tion. PRV positions in between
have linearly scaled maximums.
When the chiller is started, the speed is brought to 60
Hz. After it has been running for >2 minutes and the
Leav ing Chilled Liquid Temperature is within +0.3
and –0.6ºF of the Leaving Chilled Liq uid Tem per a ture
Setpoint, the ACC Board eval u ates if the speed can be
reduced. If there are no conditions above that would
inhibit speed re duc tion, the ACC Board compares the
real-time Del ta P/P, PRV Po si tion and motor speed to
the 3-di men sion al arrays stored in the Surge Map. If
the real-time ar ray does not match any previous surge
condition, the speed will be decreased 0.1 Hz ev ery 6
seconds until it is with in 1 Hz of previously plotted
surge condition array in the Surge Map. It will then be
de creased 0.1 Hz ev ery 9 seconds un til it's to the lowest
value allowed by the Surge Map. If no plotted points
are encountered, the speed is low ered until a surge is
encountered or a minimum of 30 Hz is reached.
The ACC Board uses two different methods of Surge
Detection; Delta P method and DC Link method. Surge
de tec tion is only enabled while the chiller is run ning. In
de tect ing a surge using the Delta P method, the out puts of
the Evaporator and Condenser pressure Trans duc ers are
mon i tored to detect when the dif fer ence be tween these
pres sures (Delta P) drops tran sient ly to ward Zero. This
would be indicative of a surge. A surge de tect ed by the
Delta P method must have all of the fol low ing con di tions
occur within 5 seconds to be con sid ered a valid surge: a.)
Delta P must make a neg a tive transition and exceed 3.4
PSIG for 100 Mil li sec onds. B.) Delta P must also exceed
3.5 PSIG for at least 340 mil li sec onds. C.) Delta P must
make at least 2 positive tran si tions. When this criteria
is met, Surge LED CR9 il lu mi nates for 2 seconds, in-
di cat ing a valid surge has been de tect ed. In detecting a
surge using the DC Link method, the VSD's DC Link
Current is mon i tored to detect when the cur rent drops
transiently to ward zero. This, as the case with Delta P
FORM 160.54-M1(503)
YORK INTERNATIONAL
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