YORK INTERNATIONAL
66
The function of the compressor capacity control sys-
tem is to automatically adjust the compressor pumping
capacity to balance with the cooling load at a predeter-
mined return water temperature.
Capacity is reduced by unloading one or more banks
of cylinders. Some cylinder banks are not equipped with
unloaders. This prevents the possibility of overheat-
ing, since a definite minimum volume of cool refriger-
ant gas flows through the compressor at all times dur-
ing operation regardless of load conditions.
Unloading is accomplished by preventing (blocking) the
suction gas from entering one or more of the suction
plenums of the compressor.
A line, connected to the discharge side of the compres-
sor, supplies high pressure gas to the unloader mecha-
nism which is mounted next to the associated bank of
cylinders. The unloader mechanism consists of a sole-
noid valve integrally mounted on the outside of the cover
plate, and an internal spring loaded piston.
UNLOADING
When the solenoid valve is energized, discharge gas
pressure is applied to the top of the unloader piston,
forcing it down against spring pressure. The bottom
end of the piston seats against the recessed opening
to the suction plenum, effectively blocking the flow of
gas into the cylinders. The cylinders are now unloaded.
LOADING
When the solenoid valve is de-energized, discharge
gas pressure on top of the unloader piston is relieved
to the suction plenum. The coil spring forces the piston
FAN CONTROL STRATEGY ABOVE 25°F AMBIENT
The chiller is equipped with 2 condenser fans. The stan-
dard fan control strategy is fan cycling by outdoor am-
bient temperature, with the low ambient cut-out (chiller
shut down) set at 25°F.
Above 25°F ambient, 1 fan will turn on 4 seconds after
either compressor starts. This fan will continue to run
until both compressors shut down. This fan is desig-
nated as Fan 2 (6M).
If the ambient temperature is above 45°F, one more
fan will start after either compressor has run for 30 sec-
onds. This fan will continue to run until both compres-
sors shut down or until the ambient temperature drops
to 40°F. This fan is designated as Fan 1 (5M).
Locations of the fans and a chart showing the opera-
tion outlined above is shown in Fig. 25.
For operation below 25°F, a Low Ambient Kit MUST be
installed. See page 7.
LD02006
FAN
AMBIENT ON
AMBIENT OFF
2
25°F
24°F
1
45°F
40°F
COMPRESSOR CAPACITY CONTROL
up, uncovering the recessed opening which allows the
suction gas to flow through the port and into the cylin-
ders. The cylinders are now loaded.
All cylinders equipped with unloaders will remain un-
loaded on start-up until the oil pressure has built up to
normal. On each compressor, certain cylinders do not
unload. (See Fig. 26).
* 6 cylinder compressors do not connect the loading solenoid wir-
ing on cylinders 1 & 2, effectively making them permanently loaded
in the standard unloading scheme. The loading solenoid wiring
on these cylinders is connected to additional electronics when
optional unloading is required. Cylinders 3 & 4 have no loading
solenoids and are truly permanently loaded.
CHILLER
SYS
# OF
# OF UNLOADING STEPS
MODEL
CYLINDERS
STD.
OPT.
YCAZ33BA3
1
4
5
N/A
YCAZ44BA3
2
4
YCAZ74BB3
1
6
5
6
2
4
YCAZ77CB3
1
6
5
7
YCAZ88DB3
2
6
LD02007
FIG. 26
COMPRESSOR UNLOADING SEQUENCE