York YCAZ33BA3, Руководство пользователя, Страница: 40 / 88

YORK INTERNATIONAL
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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 micropro-
cessor will automatically return to the Daily Schedule.
MANUAL
OVERRIDE
M A N U A L
O V E R R I D E
GENERAL
The user has the ability to select the type of chilled
liquid temperature control by choosing either Return or
Leaving Temperature Control. This provides the ability
to fine tune the method of control for comfort cooling or
batch/process cooling loads.
In many cases, comfort cooling will be best controlled
by RETURN WATER CONTROL. This will assure a
minimum of cycling compressors/loaders with stable
leaving chilled liquid temperatures as long as water flow
GPM is held constant and the Control Range (CR) is
correctly programmed.
LEAVING WATER CONTROL is also suitable for com-
fort cooling, but may produce slightly more cycling de-
pending upon the RATE SENSITIVITY programmed.
Optional stages of loading are recommended to reduce
cycling. In most cases, Leaving Water Control will be
more precise unless compressor cycling is encoun-
tered. “Anticipation” and timers are built into the
microprocessor’s control algorithms to eliminate com-
pressor and loader cycling enabling LEAVING WATER
CONTROL to be used in most applications. The con-
trol algorithm utilizes “PID” control.
For batch and process applications, LEAVING WATER
CONTROL will allow for precise temperature control. In
these applications chilled liquid temperature control is
more important than compressor/loader cycling. When
LEAVING WATER CONTROL is utilized, it is recom-
mended to have optional steps of loading on each com-
pressor. This assures minimum tonnage per step which
reduces the possibility of compressor and loader cycling
that is critical to precisely controlling temperature.
RETURN WATER CONTROL may also be used on
batch and process application and should provide ade-
quate control. However, it will prove to be less respon-
sive with slightly more leaving chilled liquid tempera-
ture variation. RETURN WATER CONTROL may be-
come necessary to use if too much compressor cy-
cling is noted with corresponding water temperature
fluctuation when in Leaving Water Control.
After determining the mode of control best suited for the
application (RETURN OR LEAVING WATER CON-
TROL), the micro panel must be interrogated to deter-
mine whether it is programmed for RETURN or LEAV-
ING WATER CONTROL. This can be accomplished by
pressing the OPTION key in the DISPLAY section of the
keypad. This allows the user to determine the present
mode of control without gaining access to the Micropro-
cessor Board and visually checking the sometimes diffi-
cult to determine Dip Switch position. When the OPTION
key is pressed, a message “THE FOLLOWING ARE
PROGRAMMED” will appear on the display for 3 sec-
onds. The display will then scroll through the 8 dip switch
selections, each appearing for 3 seconds. The 4th dis-
play will tell the user whether leaving or return tem-
perature is programmed on Switch 4. The 4th display
message will read either “RETURN WATER CONTROL”
or “LEAVING WATER CONTROL “ and will appear for 3
seconds. The display will then scroll through the 8 dip
switch selections, each appearing for 3 seconds.
If a change is required, position Switch #4 on dip switch
S1 on the Microprocessor Board (Fig. 12) as indicated:
RWT CONTROL: SW 4 OPEN
(left side pushed down)
LWT CONTROL: SW 4 CLOSED
(right side pushed down)
SELECTION OF RETURN OR LEAVING CHILLED LIQUID CONTROL