York YK Series, Operation And Maintenance

JOHNSON CONTROLS

7

FORM 160.76-O1 

ISSUE DATE: 6/15/2015

1

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 han-

dle 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 (Refer to 

Figure 1 on Page 7

).

The position of these vanes is automatically controlled 

through a lever arm attached to an electric motor lo-

cated outside the compressor housing. The automatic 

adjustment of the vane position in effect provides the 

performance of many different compressors to match 

various load conditions from full load with vanes wide 

open to minimum load with vanes completely closed.

SECTION 1 - DESCRIPTION OF SYSTEM AND  

FUNDAMENTALS OF OPERATION

SYSTEM OPERATION DESCRIPTION 

The YORK Model YK Chiller is commonly applied 

to large air conditioning systems, but may be used 

on other applications. The chiller consists of an open 

motor mounted to a compressor (with integral speed 

increasing gears), condenser, evaporator and variable 

flow control.
The chiller is controlled by a modern state of the art 

Microcomputer Control Center that monitors its opera-

tion. The Control Center is programmed by the opera-

tor to suit job specifications. Automatic timed start-ups 

and shutdowns are also programmable to suit night-

time, weekends, and holidays. The operating status, 

temperatures, pressures, and other information perti-

nent to operation of the chiller are automatically dis-

played and read on a graphic display. Other displays 

can be observed by pressing the keys as labeled on the 

Control Center. The chiller with the OptiView Control 

Center is compatible with an electro-mechanical start-

er, YORK Solid State Starter (optional), or Variable 

Speed Drive (optional).
In operation, a liquid (water or brine to be chilled) 

flows through the evaporator, where boiling refrigerant 

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)

FIGURE 1 - 

COMPRESSOR PREROTATION VANES