Description of system and fundamentals of
operation
System operation description
The following is a high-level description of the chiller control. It describes the overall operation.
Control Center components, chiller components and programmable setpoints are referenced. See
Figure 2 to view the chiller operation flowchart.
The YD dual compressor chiller consists of one evaporator, one condenser, two oil pumps and
two compressors. Other than capacity control, the basic operation is similar to a standard YK
Centrifugal Chiller.
The use of two compressors requires valves on the discharge line of each compressor. When a
compressor is shut down, its discharge valve is closed to prevent compressor backspin due to a gas
flow from the running compressor. An end switch at both the closed and open positions provides
indication of full open and full closed positions. The operator can manually control the valves.
Figure 1: Model YD chiller
Callout Description Callout Description
1 Compressor 1 2 Unit-mounted starter 1
3 Compressor 2 4 Unit-mounted starter 2
5 Evaporator 6 Control panel
Each compressor pre-rotation vane assembly is equipped with a potentiometer to provide vane
position. A calibration procedure ensures displayed position 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.
9Model YD Mod D with OptiView Control Center
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