FORM 150.75-NM2
53
YORK INTERNATIONAL
should equal the desired system leaving water tempera-
ture. As mentioned before, the micro will be satisfied
with a leaving water temperature. As mentioned before,
the micro will be satisfied with a leaving temperature
between 44° - 45°F unless the rate control is exceeded.
The microprocessors rate control is designed to be less
responsive in the upper half of the Control Range (i.e.
45° - 46°F) than in the lower half (i.e. 44° - 45°F). This
is to prevent overshoot.
To program the Low-Limit Water Temperature (LWT)
and the Control Range (CR), press the CHILLED LIQ-
UID TEMP/RANGE key. This display will first exhibit a
message that LEAVING WATER TEMP CONTROL is
selected and 3 seconds later automatically scroll to the
next display of LWT and CR. The cursor will stop at the
first digit of LWT. Key in the Low-Limit Water Tempera-
ture (LWT) that is acceptable in the system. See below:
The micro will accept a range of programmable values
from 15.0 - 70.0°F (See SWITCH 1, Page 39). If brine
or glycol is used in the system, chilled liquid tempera-
tures below 40°F may be desired.
To program setpoints below 40°F, Dip Switch S1, Switch
#1 on the Microprocessor Board must be properly pro-
grammed. (See Page 39.) If the switch is incorrect, when
setpoints below 40°F are entered as well as when un-
acceptable values are entered, the following message
will be displayed:
After the Low-Limit Water Temperature (LWT) is keyed
in, the lower limit of the CR (Control Range) in the dis-
play message will automatically change to a value iden-
tical to the LWT. See below:
The cursor will advance to the final entry which is the
upper limit of the CR (Control Range). This value is pro-
grammed for the highest leaving water temperature
L W T =
4 4 . 0 F
C R =
4 4 . 0
T O
5 4 . 0 F
Low-Limit Water Temperature (LWT)
O U T
O F
R A N G E
T R Y
A G A I N !
L W T =
4 4 . 0 F
C R =
4 4 . 0
T O
5 4 . 0 F
The lower limit of the CR will always
automatically equal LWT
which is acceptable in the system application. Typically
2°F above the Low-Limit Water Temperature is appro-
priate. The micro will accept a value 1° - 5°F above the
LWT for this value. 2°F above the LWT is the default
value.
Key in the upper limit of the CR and press the ENTER
key. Otherwise 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 another key is pressed.
CAUTION: Too small of a CR selection will cause com-
pressor / loader cycling. If compressor cy-
cling occurs, leaving water temperature
may vary considerably as a result of a com-
pressor that cannot restart due to the
antirecycle timer. To eliminate this, increase
the
D
T (temperature differential) of the CR
and / or program the anti-recycle timer for
a minimum of 300 seconds. If it isnt already
programmed for 300 seconds.
NOTE: Whenever reprogramming the LWT & CR,
keep in mind that the desired leaving water
temp. or target, should be midpoint of the
CR.
Normal pulldown loading is limited by a 30 sec. loading
timer between stages with loading occurring whenever
leaving water temperature is above the RATE CON-
TROL RANGE.
However, on start-up, loading will be limited to a maxi-
mum of 1 stage per minute for the first 3 minutes. The
loading timer will also be increased by the micro to 150
sec. when temperature falls to within the Rate Control
Range or the upper half of the Control Range (Between
Target and High Limit fo the CR).
The Rate Control software may prevent loading and will
cause unloading in the Rate Control Range or Control
Range if temperature drops faster that 2X the pro-
grammed Rate Sensitivity. This is to prevent overshoot.
In the lower half of the Control Range between the Low
Limit and the Target, Rate Control will cause unloading
if temperature falls faster than 1X the programmed Rate
Sensitivity. As before, this is to prevent overshoot.
Below the Control Range, unloading will be done at 20
sec. intervals until temperatures fall back into the Con-
trol Zone. Unloading is controlled by a 20 sec. timer
below the Control Zone as well as when Rate Control
calls for unloading.
Further details loading / unloading and Rate Control will
follow:
