FORM 150.40-NM20
55
YORK INTERNATIONAL
(YCHA120, 150, 175 & 200)
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-determined
return water temperature and to permit the compressor
to start under partial load. The compressor capacity con-
trol system is actuated by means of high pressure oil
from the compressor oil pump. Oil pressure to the power
element loads the associated cylinders and release of
this pressure unloads them. Control of the oil pressure
to the unloader elements is the function of the compres-
sor capacity control solenoids located on the front
handhole cover. The compressor is loaded when the
solenoid is de-energized, and unloaded when the sole-
noid is energized. Unloading is accomplished by lifting
and holding the suction valve off its seat. The gas, drawn
into the unloaded cylinders on the down stroke of the
piston, is pumped back into the suction chamber of the
compressor housing, without compression, when the pis-
ton returns on its up-stroke. All cylinders equipped with
unloaders will remain unloaded on start-up until the oil
pressure has built up to normal. On each compressor,
certain cylinders do not unload. (See Fig. 19.)
FIG. 19 – COMPRESSOR UNLOADING
CHILLER NO. OF CYLINDERS
MODEL 60 Hz 50 Hz
YCHA120
SYS 1 4 4
SYS 2 6 6
YCHA150
SYS 1 6 6
SYS 2 6 6
YCHA175
SYS 1 6 6
SYS 2 8 8
YCHA200
SYS 1 8 8
SYS 2 8 8
LD01794
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