Checking Pressure Transducers - Carrier AquaEdge 19DV Series Start-Up, Operation And Maintenance Instructions Manual

CHECK SENSOR ACCURACY
Place the sensor in a medium of known temperature and com-
pare that temperature to the measured reading. The thermome-
ter used to determine the temperature of the medium should be
of laboratory quality with 0.5F (0.25C) graduations. The sen-
sor in question should be accurate to within 2F (1.2C).
Note that the PIC6 control module, MAINTENANCE menu,
offers a temperature sensor calibration feature where the sensor
temperature can be offset. Note that only the four water tem-
peratures can be calibrated. To use this feature, place the sensor
at 32°F (0C) or other known temperature. Read the raw tem-
perature and calculate offset based on the reading seen in the
TEMP_CAL menu. Enter and execute the offset, which cannot
exceed ± 2F (1.2C).
See Fig. 2 for sensor locations. The sensors are immersed di-
rectly in the refrigerant or water circuits. When installing a
new sensor, apply a pipe sealant or thread sealant to the sensor
threads.
An additional thermistor, factory installed in the bottom of the
evaporator barrel, is displayed as Evap Refrig Liquid Temp on
the TEMPERATURES display screen. This thermistor pro-
vides additional protection against a loss of water flow.
DUAL TEMPERATURE SENSORS
For servicing convenience, there are 2 redundant sensors each
on the bearing and motor temperature sensors. If one of the
sensors is damaged, the other can be used by simply moving a
wire. The number 2 terminal in the sensor terminal box is the
common line. To use the second sensor, move the wire from
the number 1 position to the number 3 position. See Fig. 44 or
Fig. 45.
2ND STAGE
BEARING
TEMP SENSOR
Fig. 44 — Motor Housing Temperature Sensors
ELEMENT
ELEMENT
ELEMENT ELEMENT
WHT
Fig. 45 — First and Second Stage Bearing
Temperature Wiring and Motor Thermistor Wiring
1ST STAGE
BEARING
TEMP SENSOR
MOTOR TEMP
SENSOR
BLK
RED

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 loca-
tions, to ensure the proper refrigerant temperature/pressure re-
lationship. Each transducer is supplied with 5 vdc power. If the
power supply fails, a transducer voltage reference alarm oc-
curs. 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 re-
placing 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 con-
nector back on the sensor and snap into place. Check for refrig-
erant leaks.
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.
EVAPORATOR, CONDENSER, REFRIGERANT PUMP
SUCTION AND DISCHARGE, BEARING INLET AND
OUTLET PRESSURE TRANSDUCER CALIBRATION
Calibration can be checked by comparing the pressure readings
from the transducer to an accurate refrigeration gage reading.
These readings can be viewed or calibrated from the HMI
screen. The transducer can be checked and calibrated at 2 pres-
sure points. These calibration points are 0 psig (0 kPa) and be-
tween 10 and 30 psig (69 and 207 kPa). Connect pressure trans-
ducer to Schrader connection. To calibrate these transducers:
1. Shut down the compressor, evaporator, and condenser
pumps.
NOTE: There should be no flow through the heat exchangers.
2. Disconnect the transducer in question from its Schrader
fitting for evaporator or condenser transducer calibration.
For other pressure or flow device calibration, leave the
transducer in place.
NOTE: If the evaporator or condenser vessels are at 0 psig (0 kPa)
or are open to atmospheric pressure, the transducers can be cali-
brated for zero without removing the transducer from the vessel.
3. Access the PRESSURE or (if water side pressure)
HYDRAULIC STATUS screen and view the particular trans-
ducer reading. To calibrate pressure or waterside flow device,
view the particular reading. It should read 0 psig (0 kPa). If
the reading is not 0 psig (0 kPa), but within ± 5 psig (35 kPa),
the value may be set to zero from the Maintenance Menu
while the appropriate transducer parameter is highlighted.
The value will now go to zero.
50
WARNING
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