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FORM 160.79-O3
ISSUE DATE: 11/09/2018
SYSTEM OPERATION DESCRIPTION
The following is a high level description of the chill-
er control. It describes the overall operation. Control
Center components, chiller components and program-
mable setpoints are referenced. See Figure 2 on page
15 to view the chiller operation flowchart.
The YD dual compressor chiller consists of one evapo-
rator, one condenser, two oil pumps and two compres-
sors. Other than capacity control, the basic operation is
similar to a standard YK Centrifugal Chiller.
The use of two compressors requires valves on the dis-
charge line of each compressor. When a compressor
is shutdown, its discharge valve is closed to prevent
compressor backspin due to a gas flow from the
FIGURE 1 - MODEL YD CHILLER
JOHNSON CONTROLS
SECTION 1 – DESCRIPTION OF SYSTEM
AND FUNDAMENTALS OF OPERATION
1
2
6
COMPONENT
1
2
3
4
5
6
running compressor. An end switch at both the closed
and open positions provides indication of full open and
full closed positions. The valves can be manually con-
trolled.
Each compressor Pre-rotation Vane assembly is
equipped with a potentiometer to provide vane posi-
tion. A calibration procedure assures displayed posi-
tion accuracy. The vanes can be manually controlled.
Each compressor also has a Discharge Temperature
thermistor and High Pressure safety device.
There are two Liquid Line Solenoid Valves and two
Oil Return Solenoid Valves, one for each compressor.
3
5
DESCRIPTION
Compressor 1
Unit-mounted starter 1
Compressor 2
Unit-mounted starter 2
Evaporator
Control panel
4
LD20551
1
9
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