York YCWJ45EE0, Installation Operation & Maintenance, Page: 86 / 104

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YORK INTERNATIONAL
COMPRESSOR CAPACITY CONTROL
The function of the compressor capacity control system
is to automatically adjust the compressor pumping
capacity to balance with the cooling load at a pre-
determined leaving water temperature and to permit the
compressor to start under partial load.
The compressor capacity control system is actuated by
means of gas pressure from the discharge side of the
compressor. Gas pressure to the unloader piston un-
loads the associated cylinders and release of this pres-
sure loads them. Control of the gas pressure is through
capacity control solenoids on the compressor. The com-
pressor is loaded when the solenoid is de-energized,
and unloaded when the solenoid is energized.
Capacity is reduced by unloading one or more banks of
cylinders. Some cylinder banks are not equipped with
unloaders. This prevents the possibility of overheating,
since a definite minimum volume of cool refrigerant gas
flows through the compressor at all times during opera-
tion regardless of load conditions.
UNLOADING
When the solenoid valve is energized, discharge gas pres-
sure is applied to the top of the unloader piston, forcing
it down. The bottom end of the piston seats against the
recessed opening to the suction plenum, effectively block-
ing the flow of suction gas into the cylinders (blocked
suction unloading). The cylinders are now unloaded.
FIG. 29 – EVAPORATOR WATER PUMP CONTACT
CONNECTION POINT
If MANUAL OVERRIDE is selected, the evaporator wa-
ter pump contacts will immediately transition.
Connections to this contact can be made on Terminals
25 and 26 of TB1 in the power panel. The location of
these terminals is shown in Fig. 29.
If a power failure occurs which shuts the entire chiller
down, the contacts will not be allowed to close again
until 30 seconds after power is restored. This prevents
rapid cycling of the chilled water pump.
NOTE: Any inductive devices (contactor/relay coil) con-
nected to these contacts must be suppressed
with YORK P/N 031-00808 supplied by others.
Otherwise nuisance faults may occur.
CHILLER MODEL
SYS
# OF # OF UNLOADING STEPS
YCWJ YCRJ CYLINDERS STANDARD OPTIONAL
45EE0 45E00 1 4
5 N/A
55HE0 55H00 2 4
56HE0 56H00 1 4
6 N/A
2 6
66KH0 66K00 1 6
67KH0 67K00 2 6 7 N/A
77KH0 77K00
88MH0 88M00 1 8
10 N/A
99MJ0 99M00 2 8
LOADING
When the solenoid valve is de-energized, gas pressure
on top of the unloader piston is relieved to the suction
plenum. This forces the piston up, uncovering the re-
cessed opening which allows the suction gas to flow
through the port and into the cylinders. The cylinders
are now loaded.
NOTE: 6 cylinder compressors are equipped with 3 cylinder banks.
Cylinders 3 & 4 are permanently loaded cylinders and have
no unloading solenoids. If “optional” unloading is supplied,
Cylinders 1 & 2 are the first cylinders to load while cylin-
ders 5 & 6 the last to load. This provides three steps of
compressor loading / unloading. Unloading occurs in the
reverse sequence. In the “standard” loading / unloading
scheme where the compressor has 2 steps of loading /
unloading, the wiring to the unloading solenoid for cylin-
ders 1 & 2 is unconnected, effectively making 1 & 2 perma-
nently loaded cylinders.
8 cylinder compressors are equipped with 4 cylinder banks.
Cylinders 1 & 2 are permanently loaded cylinders and have
no unloading solenoids. If “optional” unloading is supplied,
Cylinders 5 & 6 are the first cylinders to load, Cylinders 3 &
4 the next to load, and 7 & 8 the last to load. This provides
4 steps of loading / unloading. Unloading occurs in the
reverse sequence. In the “standard” loading / unloading
scheme where the compressor has 2 steps of loading /
unloading, the wiring to the unloading solenoids for cylin-
ders 5 & 6 is unconnected, effectively making 5 & 6 perma-
nently loaded solenoids. In addition, the solenoids for
cylinders 3 & 4 and solenoids for cylinders 7 & 8 are wired
together to function as a single step of loading / unloading.
LD02092
LD02501