York YDAJ87HU7, Руководство пользователя, Страница: 51 / 100

FORM 150.75-NM2
51
YORK INTERNATIONAL
because in most cases a special Holiday Schedule is
only necessary once in a several month period. It also
eliminates the need for operator intervention to erase
the schedule after the holiday passes.
If an error is made while programming, press CANCEL.
This will clear all programmed (*) “holiday” days. The
schedule can then be reprogrammed.
The “0” key will not cancel out a “*” and cannot be used
for correcting a programming error.
Manual Override
When the MANUAL OVERRIDE key is pressed, the
Daily Schedule programmed into the chiller will be ig-
nored and the chiller will start-up when water tempera-
ture allows, unit switch permits, and system switches
permit.
Normally this key is not used unless an emergency
forces the chiller to require operation during a period
where the programmed Daily Schedule is calling for the
chiller to be OFF (Daily Schedule Shutdown).
Once activated, MANUAL OVERRIDE is only active for
a period of 30 minutes. It is for servicing only and is
designed so that if let on accidentally, the microproces-
sor will automatically return to the Daily Schedule.
CHILLED LIQUID CONTROL
GENERAL
The YDA chillers are built with two separate evapora-
tors designed to be field piped to discharge into a com-
mon supply mixed water line. This requires the chilled
liquid control to be from a mixed leaving water tempera-
ture sensor. This also requires that the Dip Switch S1
on both Microprocessor Boards to be programmed to
allow LEAVING WATER CONTROL. If a change is re-
quired, position Switch #4 on Dip Switch S1 on both
Microprocessor Boards (Fig. 25) as indicated:
LWT CONTROL: SW4 CLOSED
(right side pushed down)
Assure that “LEAVING WATER CONTROL” is selected
by pressing the OPTION key. The message “THE FOL-
LOWING ARE PROGRAMMED” will appear on the dis-
play for 3 seconds. The display will then scroll through
the 8 dip switch selection, each appearing for 3 seonds.
The 4th display will tell the user whether “LEAVING
WATER CONTROL” is programmed.
The chiller is designed to provide a stable desired mixed
leaving water temperature as required by the user and
is suitable for all types of applications such as comfort
cooling and batch / process loads.
The amount of compressor / loader cycling will depend
of the RATE SENSITIVITY programmed as well as the
programmed length of the anti-recycle timer. Anticipa-
tion controls and loading / unloading timers are built
into the control algorithms to eliminate cycling. Cycling
may be reduced by decreasing the RATE SENSITIV-
ITY and / or increasing the anti-recycle time. However,
MANUAL
OVERRIDE
M A N U A L
O V E R R I D E
this will make the chiller controls less responsive which
may cause a larger deviation in the mixed leaving wa-
ter temperature.
NOTE: Decreasing the RATE SENSITIVITY may be
undesirable and may cause the system to pre-
maturely go into rate control due to the micro
sensing a transient temperature fluctuation
and not allowing the chiller to load. This will
cause the mixed leaving water temperature
to rise above the desired setpoint.
Once the Dip Switch #4 on the Microprocessor Board
is properly positioned, the user will be able to view the
appropriate display when the CHILLED LIQUID TEMP
/ RANGE is pressed. This display should allow the fol-
lowing message:
To properly maintain desired leaving water temperature
in a system where water mixing is occuring, the micros
will, transparent to the user, adjust their individual leav-
ing water temperatures to as low as 40°F (standard wa-
ter control) or up to –4°F below the programmed setpoint
(brine) if the mixed water temperature requires it. The
“adjusted” temperatures will be evident from viewing the
actual leaving chilled liquid temperatures from SYS 1/2
and SYS 3/4 where individual leaving evaporator water
temperatures may fall below the setpoint.
The “lower than setpoint” leaving water temperatures
of the individual evaporators will compensate for the
water mixing and allow maintaining of mixed water
temperaures near the desired setpoint.
L E A V I N G W A T E R
T E M P C O N T R O L