Checking Pressure Transducers
There are 3 pressure tran sducers on hermetic mach ines. These determin e cooler,
condenser, and oil pres s ur e . Open-drive machin es hav e 4 transducers. These tran sducers
sense cooler press ure, condenser pr essure, oil supply pr essure, and oil su mp pressure. The oil
supply pressure and t he oil transmission su mp pressure differe nce is calculated by a d ifferential
pressure power supply m odu le on open-drive machin es. The PSIO then read s thi s differential.
In effect, then, the PS IO reads 3 pressure inputs for open-drive ma chines and 3 pressur e inputs
for hermetic machine s . T he c oo ler and condenser tran sducers are used by the PIC t o
determine refriger an t temperatures.
All pressure inputs can be calibrated, if necess ar y . It is not usually necessar y t o calibrate at
initial start-up. How ever, at high altitude locations, calibrat ion of the transducer will be
necessary to ensure the proper refrigerant temperature/pressure relationship. Each transducer
is supplied with 5 vdc po wer from a power suppl y. If the power supply fails, a transducer voltage
reference alarm will oc c ur . If the transducer readi ng is suspected of being f aul ty, check the
supply voltage. It shoul d be 5 vdc ± .5 v. If the supply vol ta ge is correct, the transdu cer should
be recalibrated or rep lac e d.
IMPORTANT: For hermet i c machines, whenever the oil pressure or the coo le r pres-
sure transducer is calibrated, the other sensor should be calibrated to prevent prob-
lems with oil differential pressure readings.