Checking Pressure Transducers - Carrier 19DV Series Installation, Operation And Maintenance Instructions

nd
1 : 2 stage bearing temperature sensor (RT40C)
st
2 : 1 stage bearing temp. sensor (RT39C)
3 : Motor winding temp sensor (RT31C)

10.7 Checking Pressure Transducers

There are 6 factory-installed pressure transducers measuring refrigerant pressure: condenser pressure,
evaporator pressure, refrigerant pump suction, discharge pressure, bearing inlet pressure, and bearing outlet
pressure.
These transducers can be calibrated if necessary. It is necessary to calibrate at initial start-up, particularly at high
altitude locations, to ensure the proper refrigerant temperature/ pressure relationship. Each transducer is supplied
with 5 vdc power. If the power supply fails, a transducer voltage reference alarm occurs. If the transducer reading
is suspected of being faulty, check the TRANSDUCER VOLTAGE REF supply voltage. It should be 5 vdc ± 0.5 v
as displayed in MAINTENANCE MENU >> MAINTENANCE OTHERS, where all the transducer voltages are
shown.
If the TRANSDUCER VOLTAGE REF supply voltage is correct, the transducer should be recalibrated or replaced.
Also check that any external inputs have not been grounded and are not receiving anything other than a 4 to 20
mA signal.
TRANSDUCER REPLACEMENT
Since the transducers are mounted on Schrader-type fittings, there is no need to remove refrigerant from the
vessel when replacing the transducers. Disconnect the transducer wiring. Do not pull on the transducer wires.
Unscrew the transducer from the Schrader fitting. When installing a new transducer, do not use pipe sealer (which
can plug the sensor). Put the plug connector back on the sensor and snap into place. Check for refrigerant leaks.
WARNING: Be sure to use a back-up wrench on the Schrader fitting whenever removing a transducer, since the Schrader
fitting may back out with the transducer, causing a large leak and possible injury to personnel.
Fig 61 – Motor housing temperature sensors
111