YORK INTERNATIONAL
6
FORM 160.54-O2(1102)
FORM 160.54-O2(1102)
7
YORK INTERNATIONAL
1
the I/O Board section of this book. Also, “P” com-
pressor applications are equipped with a High Speed
Thrust Bearing Limit Switch instead of the Proximity
Probe supplied on other compressors. This device de-
tects abnormal bearing position through probe contact
instead of distance measurement as performed with
the Proximity Probe.
In operation, a liquid (water or brine to be chilled)
flows through the evaporator, where boiling refriger-
ant absorbs heat from the liquid. The chilled liquid is
then piped to fan coil units or other air conditioning
terminal units, where it flows through finned coils,
absorbing heat from the air. The warmed liquid is then
returned to the chiller to complete the chilled liquid
circuit.
7619A(D)
DETAIL A –
COMPRESSOR PREROTATION VANES
Description of System and Fundamentals of Operation
The refrigerant vapor, which is produced by the boil-
ing action in the evaporator, flows to the compressor
where the rotating impeller increases its pressure and
temperature and discharges it into the condenser. Wa-
ter flowing through the condenser tubes absorbs heat
from the refrigerant vapor, causing it to condense. The
condenser water is supplied to the chiller from an ex-
ternal source, usually a cooling tower. The condensed
refrigerant drains from the condenser into the liquid
return line, where the variable orifice meters the flow
of liquid refrigerant to the evaporator to complete the
refrigerant circuit.
The major components of a chiller are selected to
handle the refrigerant, which would be evaporated at
full load design conditions. However, most systems
will be called upon to deliver full load capacity for
only a relatively small part of the time the unit is in
operation.
CAPACITY CONTROL
The major components of a chiller are selected for full
load capacities, therefore capacity must be controlled
to maintain a constant chilled liquid temperature leav-
ing the evaporator. Prerotation vanes (PRV), located at
the entrance to the compressor impeller, compensate
for variation in load (See Detail A).
The position of these vanes is automatically con-
trolled through a lever arm attached to an electric
motor located outside the compressor housing. The
automatic adjustment of the vane position in effect
provides the performance of many different compres-
sors to match various load conditions from full load
with vanes wide open to minimum load with vanes
completely closed.
