FORM 150.75-NM2
77
YORK INTERNATIONAL
COMPRESSOR CAPACITY CONTROL
The function of the compressor capacity control system
is to automatically adjust the compressor pumping ca-
pacity to balance with the cooling load at a pre-deter-
mined return water temperature and to permit the com-
pressor to start under partial load. The compressor ca-
pacity control system is actuated by means of gas pres-
sure from the discharge side of the compressor. Gas
pressure to the power element loads the associated
cylinders and release of this pressure unloads them.
Control of the gas pressure to the unloader elements is
the function of the compressor capacity control sole-
noids located on the front handhole cover.
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 (blocked suction unloading). The
cylinders are now unloaded.
NOTES:
1. 6 cylinder compressors do not connect the loading solenoid wiring on cylinders 1 & 2, effectively making them permanently loaded in the
standard unloading scheme. The loading solenoid on these cylinders is connected to additional electronics for optional extra steps of
unloading. Cylinders 3 & 4 have no loading solenoids and are truly permanently loaded cylinders.
2. 8 cylinder compressors do not connect the loading solenoids on cylinders 5 & 6, effectively making them permanently loaded in the
standard unloading scheme. The loading solenoids on cylinders 3 & 4 and 7 & 8 are jumpered together and connected to the Relay
Output Board to function together as a single step of unloading in the standard unloading scheme. Loading solenoids on 5 & 6, 3 & 4 and
7 & 8 are connected to additional electronics for extra steps of unloading. Cylinders 3 & 4 have no unloading solenoids and are truly
permanently loaded cylinders.
Optional unloading connects all loading solenoids to individual Relay Output Board outputs to provide extra steps.
FIG. 36 COMPRESSOR UNLOADING SEQUENCE
LOADING
When the solenoid valve is de-energize, gas pressure
on top of the unloader piston is relieved to the suction
plenum. The coil spring forces the piston up, uncover-
ing the recessed opening which allows the suction gas
to flow through the port and into the cylinders. The cyl-
inders are now loaded.
NO. OF STEPS
CHILLER
SYS
NO. OF
OF UNLOADING
MODEL CYLINDER
STD. OPT.
YDAJ87HU7 1 & 3 8
YDAJ87KU6
2 & 4 6
10 16
YDAJ97KU7
YDAJ88MU6
YDAJ98MU7
1, 2,
YDAJ99MW6
3, & 4
81020
YDAJ99MU7
YDAJ99MW9
LD01948
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