60
YORK INTERNATIONAL
The function of the compressor capacity control sys-
tem is to automatically adjust the compressor pump-
ing capacity to balance with the cooling load.
Capacity is reduced by unloading one or more banks
of cylinders. Some cylinder banks are not equipped
with unloaders. This prevents the possibility of over-
heating, since a definite minimum volume of cool re-
frigerant gas flows through the compressor at all times
during 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
suction 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
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.
* Optional Hot Gas Bypass (Loadminder) will add an additional step
of capacity.
COMPRESSOR CAPACITY CONTROL
CHILLER
SYS
# OF
NO. OF STEPS
MODEL
CYLINDERS
PER SYSTEM*
YCUZ330A3
1
4
2
YCUZ440A3
2
4
YCUZ740B3
1
6
3
2
4
2
YCUZ770B3
1
6
3
YCUZ880B3
2
6
FIG. 27 – “Z” COMPRESSOR UNLOADING SEQUENCE
LD00579
6 cylinder compressors do not connect the loading so-
lenoid wiring on cylinders 1 & 2, effectively making them
permanently loaded in the “standard” unloading scheme.
The loading solenoid wiring on these cylinders is con-
nected to additional electronics when “optional” unload-
ing is required. Cylinders 3 & 4 have no loading sole-
noids and are “truly” permanently loaded.
*
Содержание YCUZ330A3
Страница 79: ...FORM 195 26 NM3 YORK INTERNATIONAL 79 LD00643...
