JOHNSON CONTROLS
9
FORM 160.79-O3
ISSUE DATE: 11/09/2018
1
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.
SECTION 1 – DESCRIPTION OF SYSTEM
AND FUNDAMENTALS OF OPERATION
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
1
3
2
4
6
5
LD20551
COMPONENT DESCRIPTION
1 Compressor 1
2 Unit-mounted starter 1
3 Compressor 2
4 Unit-mounted starter 2
5 Evaporator
6 Control panel
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