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Checking Pressure Transducers
There are 3 pressure transducers on hermetic machines. These determine cooler,
condenser, and oil pressure. Open-drive machines have 4 transducers. These transducers
sense cooler pressure, condenser pressure, oil supply pressure, and oil sump pressure. The oil
supply pressure and the oil transmission sump pressure difference is calculated by a differential
pressure power supply module on open-drive machines. The PSIO then reads this differential.
In effect, then, the PSIO reads 3 pressure inputs for open-drive machines and 3 pressure inputs
for hermetic machines. The cooler and condenser transducers are used by the PIC to
determine refrigerant temperatures.
All pressure inputs can be calibrated, if necessary. It is not usually necessary to calibrate at
initial start-up. However, at high altitude locations, calibration of the transducer will be
necessary to ensure the proper refrigerant temperature/pressure relationship. Each transducer
is supplied with 5 vdc power from a power supply. If the power supply fails, a transducer voltage
reference alarm will occur. If the transducer reading is suspected of being faulty, check the
supply voltage. It should be 5 vdc ± .5 v. If the supply voltage is correct, the transducer should
be recalibrated or replaced.
IMPORTANT: For hermetic machines, whenever the oil pressure or the cooler pres-
sure transducer is calibrated, the other sensor should be calibrated to prevent prob-
lems with oil differential pressure readings.