FORM 150.44-NM4
37
YORK INTERNATIONAL
The micro will accept a range of programmable values
between 08.0° - 36.0°F for this cut-out.
SUCTION PRESSURE CUT-OUT
The SUCTION PRESSURE CUT-OUT protects the
chiller from an evaporator freeze-up should the sys-
tem attempt to run with a low refrigerant charge. Any-
time the suction pressure drops below the cut-out point,
the system will shut down.
NOTE: There are some exceptions, where suction
pressure is permitted to temporarily drop be-
low the cut-out point. Details are outlined in the
SYSTEM SAFETIES section.
For chilled water applications, the cut-out should be
set at 44 PSIG. If glycol or brine is utilized with leaving
water temperature designs below 40°F, the cut-out
should be adjusted according to concentration. A rule-
of-thumb cut-out design is to drop the cut-out 1 PSIG
below 44 PSIG for every degree of leaving glycol be-
low 40°F. In other words, 30° glycol requires a 34 PSIG
suction pressure cut-out.
To program the SUCTION PRESSURE CUT-OUT, key
in the desired value and press the ENTER key. The
new value will be entered into memory and the display
will advance to the next programmable limit.
The micro will accept a range of programmable values
between 20-70 PSIG for this cut-out. In the COMFORT
COOLING MODE (SW1 OPEN), the cut-out is adjust-
able from 44-70 PSIG. In the BRINE & PROCESS
MODE (SW1 CLOSED), the cut-out is adjustable from
20-70 PSIG.
RATE SENSITIVITY
The RATE SENSITIVITY establishes the rate of change
of return or leaving water temperature where the micro
will override the normal 30-150 seconds per stage load-
ing rate which is based on error between setpoint and
actual temperature.
The RATE SENSITIVITY is active when the leaving
chilled liquid temperature is in the RATE CONROL
TEMP RANGE. In this range, if water temperature is
dropping faster than the RATE SENSITIVITY setting,
the micro will not load any more stages because water
temperature is dropping quickly. This provides demand
limiting and reduces loader/compressor cycling and
overshoot. If quick response is needed, RATE SENSI-
TIVITY can be programmed accordingly. When tem-
peratures are in the RATE CONTROL TEMP RANGE,
loading will occur in intervals according to both rate of
water temperature change and error in water tempera-
ture versus setpoint. This will override the typical 30-
150 seconds per stage based on error in setpoint ver-
sus actual water temperatures. If water temperature is
dropping faster than the RATE SENSITIVITY, no fur-
ther loading will result and in some cases, the chiller
will unload to slow temperature drop.
RATE SENSITIVITY is also active in the CONTROL
RANGE in RETURN OR LEAVING WATER CONTROL.
Further loading will not occur if water temperature is
dropping too fast regardless of whether temperature
calls for further loading.
Typically, this value should be programmed for
5.0°F.
Additional details for programming this control
will be discussed in the SELECTION OF RETURN OR
LEAVING CHILLED LIQUID CONTROL Section (Page
40).
NUMBER OF LOAD STEPS
The number of steps of loading must be programmed
to assure proper loading sequence and temperature
control. This is done at the factory but should be
checked against the table below:
Standard unloading requires programming for 5 steps.
Optional unloading requires 7 step selection. The
YCAZ74BB3 will actually operate only 6 of the 7
steps since one compressor is a 4 cylinder with only
one unloading solenoid.
Optional unloading requires a 2nd Relay Output Board.
No compressor changes are required.
NOTE: Hot Gas Bypass (Loadminder) should be
counted as a step for programming purposes.
Program the number of steps as required. If 5 or 7 steps
is programmed, the 0 key (05 or 07) must be pressed
first.
S U C T I O N
P R E S S U R E
C U T O U T
=
4 4
P S I G
R A T E
S E N S I T I V I T Y
=
5 . 0
F / M I N .
N U M B E R
O F
L O A D
S T E P S
= 1 0 ( E N T E R
5 , 7
O R
1 0 )
Z33BA3
Z44BA3
Z74BB3
Z77DB3
Z88DB3
STD.
5 STEPS 5 STEPS 5 STEPS 5 STEPS 5 STEPS
OPT.
N/A
N/A
6 STEPS 7 STEPS 7 STEPS