Checking Pressure Transducers - Carrier AquaEdge 19XR series Start-Up, Operation And Maintenance Instructions Manual

CHECK SENSOR ACCURACY — Place the sensor in a
medium of known temperature and compare that temperature
to the measured reading. The thermometer used to determine
the temperature of the medium should be of laboratory quality
with 0.5 F (0.25 C) graduations. The sensor in question
should be accurate to within 2 F (1.2 C).
See Fig. 2 and 3 for sensor locations. The sensors are im-
mersed directly in the refrigerant or water circuits. When in-
stalling a new sensor, apply a pipe sealant or thread sealant to
the sensor threads.
An additional thermistor, factory installed in the bottom of
the cooler barrel, will read as EVAPORATOR REFRIGERANT
TEMP on the HEAT_EX display screen. This thermistor pro-
vides additional protection against a loss of water flow.
DUAL TEMPERATURE SENSORS — For servicing con-
venience, there are 2 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 sec-
ond sensor, move the wire from the number 1 position to the
number 3 position.
Checking Pressure Transducers —
factory-installed pressure transducers measuring refrigerant
and oil pressure. There is a fifth pressure transducer measuring
pressure variations at the compressor discharge on compressors
equipped with a split ring diffuser (SRD). This transducer is
not displayed and does not require calibration.
Except for the discharge transducer, these transducers
can be calibrated if necessary. It is not usually necessary to
calibrate at initial start-up. However, at high altitude loca-
tions, it is necessary to calibrate the transducers to ensure the
proper refrigerant temperature/pressure relationship. Each
transducer is supplied with 5 vdc power from the CCM. 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 displayed in CONTROL TEST under
CCM Pressure Transducers. If the TRANSDUCER VOLT-
AGE REF supply voltage is correct, the transducer should be
recalibrated or replaced.
Also check that inputs on the CCM J5-1 through J5-6 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 re-
move refrigerant from the vessel when replacing the transduc-
ers. Disconnect the transducer wiring. Do not pull on the trans-
ducer 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.
COOLER AND CONDENSER PRESSURE TRANS-
DUCER AND OPTIONAL WATERSIDE FLOW DEVICE
CALIBRATION — Calibration can be checked by compar-
ing the pressure readings from the transducer to an accurate
refrigeration gage reading. These readings can be viewed or
calibrated from the HEAT_EX screen on the ICVC. The trans-
ducer can be checked and calibrated at 2 pressure points. These
calibration points are 0 psig (0 kPa) and between 25 and 250
psig (173 and 1724 kPa). To calibrate these transducers:
1. Shut down the compressor, cooler, and condenser pumps.
2. Disconnect the transducer in question from its Schrader
3. Access the HEAT_EX screen and view the particular
There are 4
4. A high pressure point can also be calibrated between 25
The PIC II does not allow calibration if the transducer is too
far out of calibration. In this case, a new transducer must be in-
stalled and re-calibrated. If calibration problems are encoun-
tered on the OIL PRESSURE DELTA P channel, sometimes
swapping the compressor oil discharge pressure transducer and
the oil sump pressure transducer will offset an adverse trans-
ducer tolerance stack up and allow the calibration to proceed.
116
NOTE: There should be no flow through the heat
exchangers.
fitting for cooler or condenser transducer calibration. For
oil pressure or flow device calibration, leave the transduc-
er in place.
NOTE: If the cooler or condenser vessels are at
0 psig (0 kPa) or are open to atmospheric pressure, the
transducers can be calibrated for zero without remov-
ing the transducer from the vessel.
transducer reading (the EVAPORATOR PRESSURE or
CONDENSER PRESSURE parameter on the HEAT_EX
screen). To calibrate oil pressure or liquidside flow
device, view the particular reading (CHILLED WATER
DELTA P and CONDENSER WATER DELTA P on the
HEAT_EX screen, and OIL PUMP DELTA P on the
COMPRESS screen). It should read 0 psi (0 kPa). If the
reading is not 0 psi (0 kPa), but within ± 5 psi (35 kPa),
the value may be set to zero by pressing the
softkey while the appropriate transducer parameter is
highlighted on the ICVC screen. Then press the
softkey. The value will now go to zero. No high end
calibration is necessary for OIL PRESSURE DELTA P or
flow devices.
If the transducer value is not within the calibration
range, the transducer returns to the original reading. If
the pressure is within the allowed range (noted above),
check the voltage ratio of the transducer. To obtain the
voltage ratio, divide the voltage (dc) input from the
transducer by the TRANSDUCER VOLTAGE REF
supply voltage signal (displayed in CONTROL TEST
menu in the PRESSURE TRANSDUCERS screen) or
measure across the positive (+ red) and negative
(– black) leads of the transducer. For example, the
condenser transducer voltage reference is measured
at CCM terminals J2-4 and J2-6, the condenser trans-
ducer voltage input. The input to reference voltage
ratio must be between 0.80 and 0.11 for the software to
allow calibration. Pressurize the transducer until the
ratio is within range. Then attempt calibration again.
and 250 psig (172.4 and 1723.7 kPa) by attaching a regu-
lated 250 psig (1724 kPa) pressure (usually from a
nitrogen cylinder). The high pressure point can be
calibrated by accessing the appropriate transducer param-
eter on the HEAT_EX screen, highlighting the parameter,
pressing the softkey, and then using the
SELECT
or
INCREASE DECREASE
value to the exact pressure on the refrigerant gage. Press
the ENTER softkey to finish the calibration. Pressures at
high altitude locations must be compensated for, so the
chiller temperature/pressure relationship is correct.
SELECT
ENTER
softkeys to adjust the