157
NOTE: If the PWM valve fails in the close position, the
compressor suction line will isolate and the compressor will
pulldown into a continuous vacuum. It is recommended
that a pressure transducer be installed to the body of the
compressor for monitoring crankcase pressure by the system
controller and should be set up to trip the compressor off if
in a vacuum for more then 120 seconds.
PWM VALVE CONFIGURATION
The PWM valve modulation cycle is controlled by the smart
controller. The smart controller configuration DIP switches
must both be placed in the upward position to send the cor-
rect PWM signal to the PWM valve. This should be done
prior to powering up the smart controller.
The system controller measures temperature or pressure to
calculate the needed compressor capacity and communicates
that capacity to the smart controller via a 1-5 VDC analog
signal as shown by the system curve. See Fig. 42.
NOTE: A control signal less then 1 VDC will result in a
compressor capacities < 20%. Do not allow the control volt-
age signal to drop to zero volts. Zero volts represents 0%
compressor capacity.
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