Carrier 19XL - Manual (Page 52)

General
The 19XL hermetic centrifugal liquid chiller contains a microprocessor-based control center
that monitors and controls all operations of the machine. The microprocessor control system
matches the cooling capacity of the machine to the cooling load while providing state-of-the-art
machine protection. The system controls cooling load within the set point plus the deadband by
sensing the leaving chilled water or brine temperature, and regulating the inlet guide vane via a
mechanically linked actuator motor. The guide vane is a variable flow prewhirl assembly that
controls the refrigeration effect in the cooler by regulating the amount of refrigerant vapor flow
into the compressor. An increase in guide vane opening increases capacity. A decrease in
guide vane opening decreases capacity. Machine protection is provided by the processor which
monitors the digital and analog inputs and executes capacity overrides or safety shutdowns, if
required.
PIC System Components
The Product Integrated Control (PIC) is the control system on the machine. See Table 1 . The
PIC controls the operation of the machine by monitoring all operating conditions. The PIC can
diagnose a problem and let the operator know what the problem is and what to check. It
promptly positions the guide vanes to maintain leaving chilled water temperature. It can
interface with auxiliary equipment such as pumps and cooling tower fans to turn them on only
when required. It continually checks all safeties to prevent any unsafe operating condition. It