York YMC2 A, Operation And Maintenance

JOHNSON CONTROLS

7

Form 160.78-O1 

Issue date: 05/19/2021

1

Section 1 - System fundamentals

Figure 1 - 

YMC

2

 chiller components

TRANSFORMERS

CONDENSER

COMPRESSOR

OPTIVIEW

CONTROL

PANEL

COMPACT

WATER

BOXES

VSD

COOLANT

PIPING

SIGHT

GLASS

LIFTING

OPENINGS (4)

MAGNETIC BEARING

CONTROLLER

DIRECT-DRIVE

MOTOR

VSD PANEL

EVAPORATOR

LD14022

System components

The YORK Model YMC

2

 Centrifugal Liquid Chiller 

is completely factory-packaged including evaporator, 

condenser, compressor, motor, OptiView

TM

 Control 

Center, and all interconnecting unit piping and wiring. 

See 

Figure 1

.

Compressor

The compressor is a single-stage centrifugal type pow-

ered by a hermetic electric motor, on a common shaft 

with a cast aluminum, fully shrouded impeller. The im-

peller is designed for balanced thrust and is dynamically 

balanced and over-speed tested. The compressor model 

number includes gas path revision level at the end of the 

model string. Gas path revision level A includes pre-ro-

tation vanes. Gas path revisions B has fixed inlet vanes.

Motor

The compressor motor is a hermetic permanent magnet 

high speed design with magnetic bearings. The com-

pressor impeller is overhung from the end of the motor 

shaft and has no bearings of it's own.

The motor includes angular contact ball bearings only 

for control of the rotor during shutdown after rotation 

is stopped or during shutdown due to loss of power to 

the magnetic bearings.
The bearing control center maintains proper shaft posi-

tion in the magnetic bearings and counts events where 

the touchdown ball bearings may have been contacted 

during shaft rotation to alert the operation where a bear-

ing check may be necessary. The condition of the touch-

down bearings can be assessed by qualified service tech-

nicians electronically without opening the unit.

Ensure power is removed from the input 

side of the VSD at all times when the 

chiller is under vacuum (less than atmo-

spheric pressure). The VSD maintains 

voltage to ground on the motor when the 

chiller is off while voltage is available to 

the VSD. Insulating properties in the mo-

tor are reduced in vacuum and may not 

insulate this voltage sufficiently.