FORM 150.60-NM4
YORK INTERNATIONAL
43
If this message is incorrect, see the “SELECTION OF
RETURN OR LEAVING CHILLED LIQUID CONTROL”
section (Page 41) for instructions to reprogram the Mi-
croprocessor Dip Switch S1, Switch #4.
The display will then scroll to a second message & hold:
This message will display the user’s “Design Leaving
Water temperature” (LWT) Setpoint (44.0°F in the sam-
ple above). Even though return water temperature con-
trol is being utilized, the object is to provide constant
design leaving water temperature. It is the “Design Leav-
ing Water Temperature” Setpoint (LWT) which must be
programmed into the microprocessor.
Also included in this message is the “CONTROL RANGE”
(CR). The “CONTROL RANGE” is the temperature range
which loading/unloading will take place. The lower limit
of the CONTROL RANGE is always equal to the setpoint
and automatically appears when the setpoint is keyed
in. The upper limit of the CR must be programmed.
In the above sample message, with a “CR = 44.0 to
54.0°F”, the chiller will be completely off at a return water
temperature of 44.0°F and fully loaded at a return water
temperature of 54.0°F. Partial loading will occur in equal
temperature intervals between 44° and 54°. Unloading
will occur as return temperature drops below 54°F with
the chiller cycling completely off at 44°F. These tem-
peratures provide a Control Range differential of 54.0 -
44.0 = 10.0°F.
Once the upper limit of the CR is programmed, the “CON-
TROL RANGE” (CR) differential Must Always equal the
actual water temperature drop (DT) across the evapora-
tor with the chiller completely loaded. Keep this in mind
when programming the high end of the CR. In many cases,
due to improper flows, actual temperature drop occurs
across the evaporator (DT) will not equal design. For
proper operation, adjust flow as needed or program the
“CONTROL RANGE” as needed. However accomplished,
the “CONTROL RANGE” differential Must equal the evapo-
rator temperature drop when fully loaded or leaving water
temperatures well above or well below the desired
setpoint will result.
To program the Chilled Liquid Setpoints, press the
CHILLED LIQUID TEMP/RANGE key. The display will
first exhibit a message that
“RETURN WATER TEMP
CONTROL” is selected and 3 seconds later automat-
ically scroll to the next display of LWT and CR. The cur-
sor will stop at the first digit of LWT. Key in the “Design
Leaving Water Temperature” (LWT) that is required in
the system. See the following:
Design Leaving
Water Temperature
After the Design Leaving Water Temperature (LWT) is
keyed in, the lower limit of the CR (Control Range) in the
display message will automatically change to a value
identical to the “LWT”. See below:
The lower limit of the CR will
always automatically equal LWT.
The cursor will advance to the final entry which is the
upper limit of the CR (Control Range). This value must
be programmed to equal the design LWT plus the CR
differential (
∆
T across the evaporator fully loaded). In the
above examples it would be 44.0 + 10.0 = 54.0°F.
Key in the upper limit of the CR and press ENTER. Oth-
erwise the new values will not be entered into memory.
After pressing the ENTER key, the display will continue
to show the LWT and Control Range message until an-
other key is pressed.
The micro will accept a range of programmable LWT val-
ues from 10.0 - 70.0°F (See “SWITCH 1 “, Page 29). It
will also accept a value for the upper limit of the CR of 4
- 20°F above the LWT Setpoint.
If brine or glycol is used in the system, chilled liquid
temperatures below 40°F may be desired. To program
setpoints below 40°F. Dip Switch S1, Switch #1 on the
Microprocessor Board must be properly programmed.
(See Page 28, Fig. 12). If the switch is incorrect, when
setpoints below 40°F are entered as well as when unac-
ceptable values are entered, the following message will
be displayed.
Loading/Unloading is limited by a 30 sec. loading/un-
loading timer between stages, with loading/unloading
occurring according to the difference between return wa-
ter temperature and the LWT Setpoint. However, on
start-up loading will be limited to a maximum of 1 stage
per minute for the first 3 minutes. The 30 sec. loading
timer may also be overridden by the micro if temperature
is in the Rate Control Range or the Control Range (CR).
L W T =
4 4 . 0
F
C R =
4 4 . 0
T O
5 4 . 0
F
L W T =
4 4 . 0
F
C R =
4 4 . 0
T O
5 4 . 0
F
L W T =
4 4 . 0
F
C R =
4 4 . 0
T O
5 4 . 0
F
O U T
O F
R A N G E
T R Y
A G A I N !
